d’Hoop, Caring for Swifts in Brussels Crossing Worlds in Buildings Caring for Swifts in Brussels Ariane d’Hoop Université Saint-Louis – Bruxelles, CESIR Université de Liège, SEED HUMANIMALIA 14.1 (Fall 2023) Abstract: Holes in the houses of Brussels, as in other buildings across Europe, have long been the preferred nesting sites of the common swift (Apus apus), a bird famous for its fast flight and for spending most of its life on the wing. For several decades, however, urban construction and renovation has led to the destruction of swifts’ breeding sites, contributing significantly to their disappearance, and have prompted amateur naturalists to spatial interventions in ways that they hope the birds will accept. This essay explores this form of care that is forging a new path through the more-than-human city. It starts with an account of how swifts “story” the cavities they inhabit, and then describes the engagement of a devoted swift caretaker with the birds’ astute knowledge of buildings and their meaningful worlds. Moving across sites in Brussels, the essay articulates how an attentiveness takes shape between swifts, their storied-places, and the human caretakers who learn about them, as well as the tensions and contradictions that arise. Such a care practice involves noticing and experiential learning, it requires conveying importance to unfamiliar interlocutors, and leads both to the reactivation of architectural heritages and pleasure at aesthetic encounters with the birds. In some cases, the employment of nest boxes and other technologies may also risk greenwashing ecologically harmful operations. Caring for swifts, the essay concludes, involves a reciprocal co-becoming at specific architectural interfaces, through attentive and imaginative practices. These modes of attention and of imagination enable material interventions in buildings with a fuller appreciation of swifts’ storied worlds. Keywords: multispecies studies, urban ecology, care, storied-places, attentiveness, common swift Bio: Ariane d’Hoop studied spatial arrangements in performing arts and then completed a joint PhD in architecture (Université Libre de Bruxelles) and anthropology (University of Amsterdam). She has developed a micro- ethnographic attention to the materiality of places, most of them in Brussels, to explore how it matters in situated social practices. In her first monograph, The Slightest Attachment (Transcript, 2023), she examines the role of spatial arrangements in a community psychiatric care practice. Her current work focuses on spatial interventions, mostly by amateur naturalists, in response to animal presences and vulnerabilities in cities. Email: ariane.dhoop@gmail.com ORCID: 0000-0002-5093-3867 Copyright © 2023 Ariane d’Hoop This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Humanimalia 14, no. 1 (2023): 43–82. DOI: 10.52537/humanimalia.13265 mailto:ariane.dhoop@gmail.com https://orcid.org/0000-0002-5093-3867 http://doi.org/10.52537/humanimalia.13265 d’Hoop, Crossing Worlds | 45 Humanimalia 14.1 (2023) Amusive birds! Say where your hid retreat  —  Gilbert White, The Natural History of Selborne  In a short amateur video, filmed in a Brussels street in the bright, early hours of one of the first days of May, the camera points towards the gable of a house, a corner that would not usually catch one’s eye. We suddenly hear and glimpse ten or so small, black birds sweeping over the house in quick flight. The filmmaker comments: “7:53 AM. After feeding for an hour, first attempts to find the holes.”1 Some of the birds suddenly plunge into the gable, just under the edge of the roof, and charge the spot, violently hitting their bodies against it before bouncing back. A few seconds later, they strike against the freshly rendered wall. During the five vid- eos filmed there that day, we see the birds coming back, again and again, persisting in trying to enter holes that are no longer there. Each spring, they used to return from their nine-month-long mi- gration in sub-Saharan Africa to that same cavity. Now they find it cemented over. These “amusive” birds, called common swifts (Apus apus, hereafter swifts), are admired for flying “with an astonishing lightness and with the speed of the wind”, and for the way they appear to “swim slowly in the air”.2 They spend most of their life in flight through the immensity of the sky (fig. 1). However, less famous than their flight is their vital need to cram themselves into small dark holes during the breeding season. Their extreme speed makes it hard to catch sight of them as they enter their nesting hole, that is, if there is still a hole for them to enter. Whether through negligence or deliber- ate efforts, in recent decades their nesting sites have been increas- ingly destroyed by changes in the construction and renovation of buildings. 1 Martine Wauters (@swiftlady8019), “Martinets sans abri (4): recherches vaines et... Fau- con pèlerin!” YouTube, 6 May 2020, 4:55. https://youtu.be/INIoUFMrVCA. My translation. 2 Dubois, Planches coloriées, 30. https://youtu.be/INIoUFMrVCA Figure 1: A swift flying in the sky above Brussels, June 2020. Photograph by Luca de Carli. Used with permission. d’Hoop, Crossing Worlds | 47 Humanimalia 14.1 (2023) When Buildings Prove Fatal Records of swifts continually crisscrossing the clouds in Brussels date back to 1921, but their relationship with the city is much older than that.3 Swift experts estimate that these birds have specialized in nesting in the holes and cracks of human-made houses for 10,000 years, as long as these structures were built over four metres tall. In Europe, their population expanded together with the edification of monuments during antiquity and their construction techniques.4 In the nineteenth century, they were called “wall swifts” (“martinets de muraille”), since they inhabited old edifices in the crevices of church towers or ancient castles (fig. 2).5 In Belgium, swifts mostly live in cities, of which Brussels is one of the most significant. In contrast with many other birds, they still inhabit the city centre and other historic districts densely populated by hu- mans. In the early 2000s, between 1,200 and 2,400 breeding pairs were estimated to live in the city. Cavities are hardly visible from the ground, and this makes the inventory of breeding sites difficult and the numbers imprecise.6 Recent monitoring has indicated that be- tween 1992 and 2020 the number of swifts in Brussels dropped by 42 per cent, and a similar decline has been observed across Europe.7 Scientists attribute this decline to several phenomena. First, their migration towards south-east Africa is perilous and may be even more so depending on the climate conditions. Moreover, the fact that swifts are away nine months of the year plays to their disadvan- tage. Their places are too easily neglected and destroyed during their long absence. If a pair’s traditional site is no longer available, adopt- ing another breeding place is extremely difficult for them. Second, as 3 Coopman, “Les Oiseaux bruxellois”. 4 Genton and Jacquat, Martinet noir, 129, 132–33. 5 Dubois, Planches coloriées, 30. 6 Weiserbs and Jacob, Oiseaux nicheurs. 7 Paquet, Monitoring; Schaub, Meffert and Kerth “Nest-boxes”. The decline in swift popu- lations has recently been reported in twelve European countries (Weiserbs et al., “Popu- lation et habitat”, 88). It is estimated at 21 per cent between 2007 and 2016, but because the loss has not reached an average of 20 per cent since 1980, the swifts’ status for the IUCN Red List remains of “Least Concern”. See BirdLife International, “Apus apus”, The IUCN Red List of Threatened Species (2016). https://doi.org/kbn5. Figure 2: “Martinet de Muraille”. Plate 31 from Charles Fréderic Dubois, Planches coloriées des oiseaux de la Belgique et de leurs œufs, vol. 1 (Brussels: C. Muquardt, 1854). d’Hoop, Crossing Worlds | 49 Humanimalia 14.1 (2023) numerous studies suggest, insectivorous bird species such as swifts also depend on abundant insect populations to feed themselves and their young, and so to ensure successful breeding.8 Starvation may thus be another cause of death, as flying insects have signifi- cantly declined due to intensive industrial farming and the use of in- secticides, or in cities where insect populations are made vulnera- ble due to the lack of adequate vegetation, or light pollution.9 When undernourished, swifts become much more vulnerable to preda- tors, such as falcons, sparrowhawks, owls, martens, weasels, or cats. Third, swifts’ vital dependence on human buildings is seen, in many places, as a major reason for their decline.10 The evidence for this lies in the observation that all urban bird species that depend on man- made structures have seen their numbers plummet, as the evolu- tion of current construction techniques and materials offer fewer nesting opportunities in comparison to older buildings. The most recent reports indicate that the number of birds breeding in cavi- ties in Brussels has dropped by an average of 74 per cent between 1992 and 2018.11 Indeed, when the swift’s decline was first detected in Brussels, it was particularly districts where lots of renovations had been car- ried out that were affected.12 These renovations entail the replace- ment of old buildings with edifices whose flat surfaces are made of concrete, manufactured panels or glass, without recesses or pro- trusions.13 These buildings’ minimalist style leaves no room for other cavity-nesting birds or nonhuman animals that have been making their homes in the crevices of our buildings for centuries.14 Plus, next to public urban renewal programmes that have been implemented 8 Tallamy and Shriver, “Declines in Insects”. 9 Paquet, “Campagne de recencement”; Tallamy and Shriver, “Declines in Insects”. 10 Weiserbs et al., “Population et habitat”; Wauters, “Mesures pratiques”; Schaub, Meffert, and Kerth “Nest–boxes”, 165. 11 Paquet and Weiserbs, Inventaire et surveillance, 17. 12 Weiserbs and Jacob, Oiseaux nicheurs; Weiserbs et al., “Population et habitat”. 13 “Brusselization” is a term dating from the 1960s and 1970s, which refers to a major trauma among the inhabitants of Brussels: the megalomaniacal tabula rasa of entire neighbourhoods in the name of modernizing the city, led by developers who also prof- ited handsomely from it. 14 Mourmans-Leinders, Le martinet noir. 50 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) since the late 1970s, the thermal insulation of the walls and roofs of existing houses has become a focus of public authorities. In Brus- sels, the regulation dealing with the reduction of energy consump- tion in the construction sector became more apparent in the first decades of the twenty-first century,15 and the recent energy cri- sis prompts a massive insulation of most residential buildings.16 Al- though the need for renovation and to reduce carbon emissions through insulation techniques and regulations is important, its cur- rent form of implementation undermines other forms of life than human ones, regardless of their crucial dependency on the mate- riality of buildings. In short, whereas swifts’ vulnerability certainly stems from their mi- gratory and insectivorous character, urban observations foreground the destruction of their nesting site as a major threat to their dis- appearance. Swifts’ vital dependence on the human-built environ- ment, together with their discontinuous but loyal and barely notice- able presence in its holes, have rendered them highly vulnerable to the loss of their homes. Caring for Storied Places In a previous issue of this journal, philosopher Thom van Dooren and anthropologist Deborah Bird Rose proposed the notion of “sto- ried-places”. With that notion, the authors call for an attentiveness to the nonhuman storying of a place; that is, how animals “understand 15 Neuwels, “Politique de performance”. 16 In Brussels, 45 per cent of residential buildings belong to the least energy-efficient cate- gories, and the Region wants to improve this situation by 2030 through financial incen- tives (Devillers, “La Disparition”). Today, the European Union requires that all residen- tial buildings be fully insulated by 2050. For private homeowners, the offer of insulation premiums is justified by the prospect of a reduction of their heating bill. But the lack of means remains an obstacle: most of the houses that are poorly insulated belong to low-income owners who can’t afford the investment. Swifts thus trouble the notion that “urban nature” belongs to the most privileged neighbourhoods, since their dwell- ings in buildings precisely depend on the unequal distribution of housing insulation. It would be too hasty, however, to qualify this connection between endangered animals and underprivileged human residents as a kind of interspecies alliance for a more con- vivial city, because the latter don’t actively seek to keep their house permeable to heat loss or to cavity-nesting birds. d’Hoop, Crossing Worlds | 51 Humanimalia 14.1 (2023) and render meaningful the places they inhabit.”17 As they frame it, a story is not necessarily a verbal or written account, nor must it in- volve chronological descriptions. A story can also be developed by weaving connections between events while experiencing a world meaningfully. These connections emerge, for instance, on Sydney’s shorelines, when penguins faithfully return to their breeding sites, which have become lost places; when they adapt their burrows to local rock crevices; or transmit their practices of place-making to subsequent generations. From this perspective, urban places are more-than-human worlds: they’re multispecies achievements, be- ing “co-constituted in processes of overlapping and entangled ‘sto- rying’, in which different participants may have different ideas about where we have come from and where we are going.”18 To speak of “storied-places” is a plea against human exceptionalism, since it con- tends that the ability to inhabit a meaningful world is not exclusive to humans. The notion also requires deeper consideration than that of “habitat”, which limits the focus to the biophysical attributes of the sites that birds occupy.19 In this way, van Dooren and Rose’s propo- sition claims a greater “conviviality” with nonhuman animals in cit- ies: an ethics that would acknowledge alternative ways of inhabiting and making a place meaningful, in a more equitable city, perhaps especially for those whose lives are endangered. This proposition has fuelled my concern for the swifts, their nesting sites in Brussels and their destruction. The notion of “storied-places” calls for taking more seriously the swifts’ meaningful engagements with, or worlds within, the particular places they inhabit. But the case of swifts leads me to expand the proposition by adopting a slightly different focus, which raises some different questions. Swifts have intimately embedded their storying of places in human-made 17 van Dooren and Rose, “Storied-Places”, 1. This plea is part of the broader effort of these authors to reflect on species extinction as an ongoing phenomenon that is happening around us, including in our cities, as part of “a quieter systemic process of loss” (Rose, van Dooren, and Chrulew, Extinction Studies, 1). They delve into the specificities of case studies, narrate how situated processes of extinction matter and to whom, and elabo- rate on ethical responses to the issues at stake in multispecies situations. 18 van Dooren and Rose, “Storied-Places”, 2. 19 van Dooren and Rose, 10. 52 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) buildings. For generations, they have entangled their sense of place with ours. In Brussels and elsewhere in Europe, the destruction of their breeding places has engendered a commitment to maintain- ing or remaking these places in ways that the birds would best ac- cept them. In other words, the situations I have found in Brussels involve the specific relationships that the birds have formed with particular places, but also the persistent efforts by devoted people to provide nesting sites that swifts will hopefully adopt. Those ef- forts are the focus of this paper. I articulate swifts’ storying of their places along with the practices of people who are learning to care for them. If swifts have different ideas about the human-made buildings they inhabit, then there’s a lot to learn from the people who are dis- covering these ideas and dwellings, and the responses they call for. I therefore explore the actual situations in which a more careful at- tention takes shape between the birds, the buildings, and the peo- ple who encounter them there. My relational thinking comes from a body of work that focus on care practices, informed by science and technology studies. These ethnographic studies focus on the rela- tionships that develop between different beings — people, techni- cal things, animals, and others — and examines what these relation- ships produce in ongoing attempts to improve fragile situations.20 In these studies, care is not all about warm, nice, and infinitely sup- portive relationships. Caretakers rather try out specific ways of op- erating within those situations, notably by (re)arranging the spac- es.21 Here, by focusing on the forms of care for other species involved in practices of place-making, I bring out how attentive practices emerge between swifts, their storied-places and the human care- takers who learn about them. How can animal spatial practices and meanings, in this case involving swifts, be supported in the (re)mak- ing of a place? How might an attentiveness develop along with these care practices? And which tensions or contradictions do they carry? In Brussels, conservation efforts for swifts and their nesting sites rely heavily on volunteers. Martine Wauters, who filmed the video I 20 Mol, Moser, and Pols, Care in Practice. 21 d’Hoop, The Slightest Attachment. d’Hoop, Crossing Worlds | 53 Humanimalia 14.1 (2023) mentioned earlier, is a leading figure among them. Since 2010 she has been increasingly committed to the fate of these birds, to such an extent that it has become the central activity of her life, albeit un- paid. After having read the many observations she posts on her blog, “Martine(t) News”,22 I conducted a series of interviews with her and I then observed her interventions on-site. While these direct observa- tions were fruitful, in order to get a deeper sense of the situations at stake I completed them with archival research and recent grey liter- ature about the swifts in Brussels (monitoring reports, maps or local observations), documentary research into Brussels’ building types, ornithological studies about swifts spanning other European regions (natural history, descriptive biology, ethology), and technical manu- als about buildings or nest boxes. In other words, this method is less predefined and more guided by the situation under scrutiny: by what this situation requires me to learn to better understand and reflect on the worlds that take shape in those places and multispecies en- counters. This method leads me to refer to the natural sciences, as well as other, non-scientific ways of knowing, while remaining critical about certain knowledge practices, in order to weave a tale proper to the social sciences.23 This tale articulates how urban sites in Brus- sels matter for swifts and people, where their respective values and practices of place-making may entwine, clash or be reinvented. In what follows, I describe how swifts’ storied places involve the social creation of distinct cavities. Next, my attention centres on people’s engagements with specific sites, where they develop certain ways to notice, to recuperate historical artefacts, and to use technologies such as nest boxes and audio recordings. More than merely provid- ing suitable habitats, those engagements are forms of care through 22 “Martine(t) News, le blog de Martine Wauters (Belgique)”, http://martinew.canalblog. com. (“Martinet” is the French word for “swift”.) 23 Cf. Swanson, “Methods for Multispecies Anthropology”. While researching these efforts for liveable places for swifts, I found high stakes in learning from unofficial and minor forms of knowledge, where experimental engagement through lay expertise has wor- thy of relevance compared to the “true facts” to be unveiled by scientists. This obser- vation aligns with Steven Hinchliffe and Sarah Whatmore’s argument for a “politics of conviviality” in “living cities”, that is, where experts in urban design and conservation are liable to be contested by city inhabitants who have acquired day-to-day, vernacu- lar ecological knowledge. See Hinchliffe and Whatmore, “Living Cities”. http://martinew.canalblog.com/ http://martinew.canalblog.com/ 54 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) which people learn about the birds’ storying of places and propose plots, in the materiality of buildings, in the hope that they continue or reshape these storying practices. In the final section, I discuss how “paying attention” occurs as the birds and caregivers draw each other into their worlds, through tangible interventions as much as imagina- tive work. In my view, these emerging modes of attention and of im- agination, and worlds that materialize in buildings, map some of the more liveable paths through the more-than-human city.24 Swifts’ Stories: The Social Creation of Distinct Cavities Each summer, swifts animate the sky over several neighbourhoods in Brussels with tireless sarabandes. Swifts are very much at home in the air, eating, drinking, and even sleeping, grooming, and mat- ing in flight. But one thing they can hardly do on the wing is lay eggs. For that, they need a grounded place, and so they seek out particular streets, houses, holes, and the darkness therein. This is where they will settle down for the summer months. Once a hole is adopted, the nest built, and two or three eggs have been laid, the parents take turns brooding them and will then feed the nestlings with numerous airborne insects hunted beyond the colony’s terri- tory (fig. 3). Approaching the end of July, nestlings strengthen their wings and hesitantly scrutinize the outside world before entering their aerial lives. As for the parents, they take their leave for Africa soon after the last juvenile has left the nest. If they are lucky, the pair will return to the same cavity throughout their entire lifetime, which might be many years or even decades. The oldest known res- ident has been returning to the same nesting site for twenty-one years.25 While swifts’ nesting places are without a doubt indispen- sable to their reproduction, the significance of the holes goes be- yond their being useful for breeding. How do the birds inhabit them? Through which experiences and connections do they render these holes meaningful? In other words, what do we know of the way that they “story” these places? 24 Amidst a great deal of literature on this subject, the concept of zoöpolis, emerging in Berkeley in the 1990s, offers an agenda for a full appreciation of animal conditions in our cities; see Wolch, “Zoöpolis”. 25 Weitnauer, Mein Vogel. Figure 3: Two parents visiting nestlings in their nest box, installed by inhabitants in their house in the city centre. Screenshot by the author from http://ruysbroecktower.viewcam. me:8000/ on 17 June, 2020. Courtesy of Elizabeth Thornburn and Mark Pearse. http://ruysbroecktower.viewcam.me:8000/ http://ruysbroecktower.viewcam.me:8000/ 56 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) “The discovery of a suitable nesting site,” writes Ulrich Tigges, “un- doubtedly is the most important event in the life of a swift.”26 As he observes in Berlin, the borders of a colony’s territory align with the streets’ spatial layouts, such as the rows of houses that frame a few blocks. The sociality of a colony is thus first and foremost aligned with the built environment of a neighbourhood. In turn, the city block, while becoming a territory, contributes to the social inven- tion of swifts as neighbours. Indeed, they transmit its frontiers across generations. Over the summer, swifts’ flying parties involve high- pitched, piercing screams that indicate the locality to the youngest members of the colony. While analysing these “screaming parties”, Rosanne van Oudheusden found that variation in calls occurs be- tween individuals, but also between different geographical locations. Although this observation invites further research, it suggests that a territory may well be distinctive in its vocalization.27 Once drawn to that location, at dusk the youngest swifts engage in an aerial dis- play for which ornithologist David Lack coined the term “banging”: a bird alone, or sometimes followed by several others, will loop and brush against the holes in a building.28 As soon as the banging ac- tivity starts, older members of the colony come back to their cav- ities, sit at the entrance and scream at the potential intruder in or- der to signal their occupation. While passing and passing again in front of the holes and nests of the colony, the youngest in fact map which ones are occupied and who is living where within the colony’s territory.29 They engage in these jubilant rituals with great energy and screaming, but will not nest in their own cavity before coming back the next year. Thus, they sharpen their sense of place through these banging movements and screams, among the swifts of a col- ony and the blocks that they inhabit. This emplaced sociability 26 Tigges, “Spatial Behaviour”, 3–4. 27 van Oudheusden, A Call for Help. 28 Lack, Swifts in a Tower, 34–35; Genton and Jacquat, Martinet noir, 38. 29 Although Lack (Swifts in a Tower) interprets this behaviour as a search for unoccupied nesting cavities, there may be other reasons that remain little understood. Olos (“Is ‘Banging’”) observes that the more banging occurs, the less birds of prey such as kes- trels attempt and succeed in hunting swifts at the hole entrances, which leads him to interpret this behaviour as an anti-predator strategy. For Genton and Jacquat (Marti- net noir, 39), play seems to prevail over the discernment of cavity occupation. d’Hoop, Crossing Worlds | 57 Humanimalia 14.1 (2023) appears even more valuable when one knows that, during their mi- gration, the birds make very little contact with each other.30 The re- lations between older and young members of the community take shape together with the transmission and recreation of their terri- tory, bounded by the spatiality of a neighbourhood.31 And while adult swifts remain loyal to their cavity summer after summer, the young- est birds prospecting for new sites are more inclined to adopt new kinds of holes. They therefore appear as more hopeful settlers to the people who try to attract them to other crevices or nest boxes. Then, within such a territory, swifts’ storying involves cavities and their interior. While back from migration adult swifts meet their partner in the same cavity as the previous year, which thus becomes a rendez- vous point. When first adopting a new nest, a swift learns to enter it with ease and quickness, and then trains its partner by demonstrat- ing the appropriate movements.32 It takes several days of training for flight movements to be successfully attuned to a particular entrance. Partners then arrange their nest with a degree of “architectural dex- terity”33 in the darkest side of the hole. They collect light materials car- ried up by the wind over the colony site or near it, like bits of straw, feathers, small leaves, pieces of plastic, grass, scraps of paper, some- times petals, and damselflies or butterflies whose vivid colours spar- kle.34 More than a collection of materials, the nest of a pair of swifts consists, too, of secretions from their own bodies. They stick these materials with their saliva and shape their nest by turning around it, moulding it to fit the interior contours of the cavity.35 They keep build- ing the nest when the eggs are laid and stop when they hatch, and non-breeding pairs continue the nest-making process throughout the 30 Genton and Jacquat, Martinet noir, 74. 31 As Vinciane Despret (Habiter en oiseau, 163–4) notes, the creation of a neighbourhood is one of the many ways in which the territory of birds matters. And here I add: the block as a spatial configuration contributes, by its material arrangement, to the birds’ social in- vention. Such a neighbourhood allows them vigilance, too: swifts have a special scream for warning each other, as well as house martins, when a predator is approaching. 32 Genton and Jacquat, Martinet noir, 93, 95. 33 Goodfellow, Avian Architecture, 22. 34 Gory, “Recherche et utilisation”. 35 Gory “Recherche et utilisation”; Wauters “Mesures pratiques”; Lack, Swifts in a Tower, 51. 58 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) whole summer, preparing for the years to come. Thus, each nest is un- like any other: swifts create a distinct relationship with them through the attunement of their flight to the entrance and interior arrangement with their own collection of materials and secretions. But swifts’ cavities are not only singular within the territory of a col- ony or in its interior design. The birds also demonstrate the impor- tance of their home through their stubbornness in defending it. Not only do they scream out when a potential intruder passes by, but when resident swifts find a stranger in their hole (conspecifics or otherwise, such as starlings or sparrows), a fight ensues that can last more than five hours.36 Serious injuries, and in some rare cases death, may result from these vigorous fights, although playacting is not excluded from these encounters.37 These battles are another manifestation of how much swifts’ distinctive homes matter to them. And these conflicts are contingent upon “our” buildings as well: the scarcer the holes, the greater the chance of fights. From this glimpse into swifts’ connections with their dwelling places, it is notable how much their storying is imbued with sociability, and results in the creation of a distinctive place: while becoming a neigh- bour within the territory of a colony, transmitting its boundaries across generations, discovering which cavities are available or inhab- ited, and by whom, attuning their vocalizations to a location, being reunited with one’s partner after an incredibly long journey, building a nest together, defending the place with sheer stubbornness and, last but not least, sustaining a lifelong fidelity to the only site where they ever dwell. Swifts’ involvement with their nesting places also occurs through a familiarization with the space of a singular cavity, through their bodily training to enter it quickly, or when shaping the 36 I have found a few witnesses of swifts and sparrows occupying the same cavity in har- mony. Such interspecies cohabitation seems rare but deserves more acknowledgement. 37 Indeed, Lack attests that he once found a beaten swift looking dead, so he frightened its opponent away in an attempt to save the almost-beaten bird. Yet when the other bird flew away, “the apparent corpse rose up and also left the box, evidently uninjured” (Swifts in a Tower, 31). In most cases, however, these fights are a risky practice. It may happen, for instance, that house sparrows come to inhabit the hole during the absence of swifts. Once expropriated, the sparrows may take revenge by wrecking swifts’ nests, and piercing and throwing out their eggs (Genton and Jacquat, Martinet noir, 102–3). d’Hoop, Crossing Worlds | 59 Humanimalia 14.1 (2023) nest according to the layout of a hole. What to a human might seem like nothing more than dark, dusty little cavities into which the birds crawl to raise their young, in fact carry social importance and dis- tinct familiarizations. In a text entitled “More-than-Human Sociality”, Anna Tsing calls for critical descriptions that extend our curiosity into the social worlds of nonhuman others, which are not understood through human social standards.38 With these socialities belonging to other species, Tsing evokes the way landscapes can carry multi- ple contingent histories, in which humans and their plans remain im- portant but are far from being the only agent. I will come back to the conjoint histories of a site. For now, I would simply like to point out how swift sociality, as they put it in motion within a colony, a pair, or interspecies interactions, is intimately entangled with, and created by, the singular built environment in which they learn to dwell, from the configuration of a city block to the shape of a cavity. Cracks and Colonnades: Noticing, Learning, Conveying The collection of swift photographs and anecdotes that Martine shares on her blog draws readers in with an attentive curiosity for these unexpected sites. The documentation of her observations and interventions is a practice through which a form of noticing emerg- es.39 She sometimes says that she now looks at the city “with swift eyes”. As we will see, in practice this expression can mean shifts in focus and different ways of noticing. The older posts on her blog show pictures of houses, often poorly maintained, which are zoomed in on the holes and cracks around which she first heard screams and, looking up, spotted swifts’ cavi- ties. Non-breeding swifts brushing the tops of houses when banging often provide the first clues to the presence of a colony. But swifts’ nesting sites are hard to see because their entrances are impossibly small — a crack between two bricks, the slight gap in the eaves — and because the swift’s flight in and out is so quick that one must watch with undisturbed patience to perceive it. 38 Tsing, “More-than-Human Sociality”. 39 Tsing identifies different practices for developing the skill of noticing mushrooms, while learning to love them, such as painting or collecting. See Tsing, “Arts of Inclusion”. 60 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) Soon after she started to collect observations, Martine engaged in technical arrangements in order to protect nesting sites or to in- stall new ones. Whether tending to emergencies or not, she is con- stantly alert and ready to go to sites of concern. On the map she shared with me in 2020, I counted 130 interventions she made in Brussels, under or inside eaves, in holes or walls. She also estab- lished the volunteer working group, whose members monitor colo- nies or help to carry out awareness-raising actions. Her knowledge, then, comes from the accumulation of these situated experiences. Importantly, it is also supported by a network of swift enthusiasts from countries across Europe. The network consolidates learning and support, allowing members to give advice, share new scien- tific knowledge, and to meet up regularly and invite each other to visit sites abroad.40 Such a community of knowledge allows learn- ing that is both based in locality and travels across territories, where the dwellings of birds often reveal new details about the suitability of particular places. In this way, swift lovers have learnt to pay atten- tion to the birds while becoming affected by what matters to them. I became aware of the potential of such attentiveness when read- ing Vinciane Despret’s study about birds’ territories and the ornithol- ogists who multiply the many ways in which they are experienced, felt, and made significant. Learning to pay attention, she writes, is a process of “attunement” (“accorder de l’attention”): it is both “giv- ing one’s attention” and acknowledging how other beings are at- tentive; “it is another way of acknowledging importance”.41 In other words, when birds make territories, they create modes of attention to which ornithologists may in turn become attuned. This makes the birds more interesting and opens up significant differences, not only between perspectives or hypotheses, but between territories, ways of living, and ways of world-making. Returning to Martine, I recog- nize this attunement of attention to that of the birds in the way she learned to notice swifts’ places through an accumulation of obser- vations of local colonies, enlarged by those of connoisseurs from 40 The respective websites of members of that network are each more enthralling than the next. A list is available here http://www.commonswift.org/others_english.html. Ac- cessed on April 24, 2020. 41 Despret, Habiter en oiseau, 15. http://www.commonswift.org/others_english.html d’Hoop, Crossing Worlds | 61 Humanimalia 14.1 (2023) abroad. She also used to watch over her interventions, checking to see if the birds would come back and that nothing bothers them. Yet in recent years, the volume of requests has become so overwhelm- ing that little time remains to see if all goes well in those places. Moreover, the process of noticing and learning is sometimes not enough. The work of preserving or providing homes for swifts re- quires conveying this field knowledge and its importance to unfamil- iar interlocutors. This occurred as we were sitting in the construction site cabin, behind a monumental art and history museum (Musée du Cinquantenaire), together with the site managers of the govern- mental organization managing the state’s properties (Régie des Bâ- timents). This museum is a persistent mark left by Belgium’s colonial power and displays a collection of archaeological artefacts and art- works from non-European cultures. In 2015, ornithologists discov- ered a colony of swifts living in the cracks in the curved colonnade on either side of the museum (fig. 4a & b). There, swifts offer an impressive spectacle, with their acrobatic flights around the mosaics and their cries that reverberate among the stones of the colonnade. Since their presence has been docu- mented, it was also mentioned in the planning permission, which subsequently requires a meeting in order to see if the upcoming restoration of the colonnade will affect the birds. The roof is prone to leaking, but before the necessary repairs can be undertaken, it is necessary to ascertain that they will not disturb the nesting sites. For Martine, the stakes of this meeting are even higher than protect- ing the nests. Not only does she care about this astonishing colony, but, knowing the numerous, huge buildings that the Régie manages, she also envisions the possibilities that may arise if her interlocu- tors were to be receptive to the matter of urban wildlife. She thus at- tempts to magnify the meeting’s importance. From the outset, she has placed on the table two wooden artefacts — a swift and a square with a hole in it — along with her laptop featuring blog posts about previous interventions, and annotated pictures of the building and its colonnades (fig. 5). With these objects she concretely explains the situation: she talks about the birds, their needs, the specific holes Figure 4 (opposite): a) The curved colonnade of the Musée du Cinquantenaire, Brussels. b) Holes above the mosaic. Figure 5 (above): Martine’s props for making swifts’ presence concrete and technical. All photographs by the author. 64 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) where their presence has been documented. Her arm dives down and then swoops back up and turns around. She is showing swifts’ movements as they would leave and enter the holes, and the space they require to do so. The meeting goes well: all agree to make sure that no works will oc- cur during the breeding season, and that no remaining infrastruc- ture will prevent access to the cracks. I am surprised to discover how these site managers listen at length about swifts, look at leaflets about the birds’ ethology, and become interested in different forms of nesting boxes. I am moved by the feeling that something comes to truly matter, which did not an hour ago. We then go up under the colonnade to take a closer look in situ, which manifested even more care. Martine indicates the nesting sites, and where and how the swifts fly. In doing so, she stirs her interlocutors’ imaginations: she creates a “fictional presence” of the birds while they are away. From there we can also notice the actual sizes of the cracks and how spotlights aimed at the mosaics may be disruptive for the birds. The meeting concludes with further commitments. They envisage the in- stallation of nest boxes on the museum’s vast roof for black redstarts or grey wagtails, these birds having been documented on the site. They also extend their concerns to other buildings managed by the Régie. The organization includes a service devoted to sustainability, yet the reduction of energy consumption is, again, a leading priority. But that meeting may induce earlier changes. I observed how the site managers’ interest took shape, along with Martine’s budding joy when sensing her interlocutors’ responsiveness. She managed to make this happen, when she mimicked the birds’ movement, talked about their ways of life, used objects that gave a concrete idea, showed existing solutions, or the birds’ behaviour when on site and, when necessary, shifted from these stirs of imagination to a technical and architectural language. It was through these con- crete ways of doing that a sense of importance was passed on to the others. Of course, such a sense of importance is not always so readily manifested and conveyed. And perhaps my presence as an observer also amplified it. But when it does, these ways of doing d’Hoop, Crossing Worlds | 65 Humanimalia 14.1 (2023) foster significance. Conveying, here, is not simply communicating information, but, as its popular Latin root conviare reminds us, it of- fers an invitation “to accompany on the way”. These approaches fos- ter commitment in people; they spread and amplify concerns, first embedded in that building and situation, then opening on to others. Putlog Holes and Towers: Reactivating Heritages Certain historical artefacts belong to the architectural specificities that Martine and other swift lovers have learned to notice. In the nineteenth century, Brussels saw tremendous development with the erection of the characteristic terraced townhouses that swifts, among other birds, came to particularly enjoy. Most of these mai- sons bruxelloises were built between the 1850s and the 1930s, at a time of great industrial prosperity. These houses are hospitable to swifts, mostly because they offer more spaces and cracks, but also due to a detail of their architecture. Below the eaves of the maisons bruxelloises, a series of holes have been inserted at regular intervals, called “putlog holes” (“trous de boulins”, fig. 6a). These holes have existed at least since the Mid- dle Ages, and were particularly common in nineteenth century con- structions in Belgium and northern France. Until the inter-war pe- riod, they were mandatory in most municipalities in Brussels. Putlog holes were first and foremost used to insert the ends of beams, to support scaffolding for finishing touches or repairing façades, and oc- casionally to insert pulleys for raising furniture (fig. 6b). “Putlog cov- ers” (“cache-boulin”) were often placed over the holes, to be removed when the holes were needed. At first, putlog covers were made of cork, but from the 1870s they were attached by a hinge at the top, as large-scale and inexpensive production developed models either in cast iron or in stamped or molten zinc (fig.6c).42 Putlog covers are shaped as ornaments featuring stars, rosettes, and often mascarons such as frightening human or animal faces (here mostly lions or dogs), originally intended to frighten away evil spirits. If the covers were not stolen to be sold for scrap metal, they were often slightly ajar or 42 Hennaut and Demanet, Bois et Métal, 166–67. Fig. 6: a) (opposite, top) Putlog holes in the façades of typical Brussels townhouses. Photograph by the author. b) (opposite, bottom) Mid- nineteenth-century putlog hole used to hold an I-beam in Charleroi, Belgium (2015). Photo credit: Jmh2o, CC BY-SA 4.0, via Wikimedia Commons. c) (this page) Putlog holes with covers in Brussels. Photograph by the author. https://creativecommons.org/licenses/by-sa/4.0 https://commons.wikimedia.org/wiki/File:Charleroi_-_trou_de_boulin_-_utilisation_actuelle.jpg 68 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) corroded by rust, leaving open a small passage to the hole. From the turn of the twentieth century, architects’ tastes led them to leave the holes fully open and to play with polychromed materials for embel- lishing the borders. Nowadays, putlog holes and their covers are lit- tle known. They are hardly appreciated as cultural heritage, and liter- ature about them is scarce. Yet, once brought to your attention, they are noticeable everywhere in the suburbs of Brussels. To begin noticing putlog holes is to begin looking at Brussels’ houses with swifts’ eyes. Almost always more than five metres above street level — a swift’s minimum requirement — putlog holes are very pop- ular among the birds. While swifts are sensitive to light at the nest, they find obscure cavities in putlog holes, as they are about thirty centimetres deep. Owing to the covers, their entrances may be quite narrow, making the hole a safe refuge by keeping bigger birds out. Smaller models (five to eight centimetres in diameter) are also inter- esting to swifts as corridors to reach spaces under roofs. In all cases, an opening of three centimetres makes the hole perfectly suitable for swifts to enter with their straight flight, or when swooping out (fig. 7). Other cavities in Brussels’ buildings are good candidates for becom- ing swifts’ dark quarters. Watching the city “with swifts’ eyes” means noticing entrances that look tiny to humans. Mostly, eaves provide large boxes that the birds first explore from their side edges. Yet swifts may also find shelter in ventilation holes whose grates have fallen off, in cracks under or above lintels or windowsills, and under fascia boards, where narrow spaces are left between the end of the wall and the side of the roof. More rarely, swifts have dwelled in roller shutter boxes, although such spaces are difficult to access for them. Martine notes that there are some “cultural” differences between Brussels’ swifts and those belonging to other landscapes, as well as between colonies, since some of them favour one sort of cavity over another.43 Putlog holes in particular are architectural technologies that are culturally, historically, and geographically specific. Today they are not well known, but swifts have long found them suitable. Their storying of places has emerged with these specific artefacts 43 Wauters, “Mesures pratiques”; Weiserbs et al., “Population et habitat”. Fig. 7: Swift diving from a putlog hole, Molenbeek municipality square, 2010. Photograph by Brigitte De Boeck and Jean-Claude Hardy. Used with their permission and that of Martine Wauters. 70 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) that are culturally situated. This is the case for different kinds of cav- ities, such as eaves, but putlog holes show even more forcefully how swifts converted a highly specific historical technology into a dwell- ing place. As Dominique Lestel argues, if technical skills and the use of tools are cultural attributes among human societies, then the making of private spaces by animals (such as nests or burrows) are part of their cultures too.44 In this way, putlog holes lie at the inter- face between local human and swift cultures. Swifts’ conversions of these holes, like other specific human-made artefacts that have come to suit their preferences, form a historical and cultural entan- glement between their world and ours. Thus, swifts and their de- fenders do not engage with “human constructions” in general, but with these discrete, specific heritages that have become meaning- ful in the swift’s world, and now gain new attention and meaning for people in their encounters with them.45 Another form of architectural heritage to which swifts draw our at- tention are towers. Not modern skyscrapers, as we have seen, but lower and older towers such as those of churches or castles. These towers are more than suitable technologies. When a colony lives in the top walls or roof of a tower, the group circles round the column, seemingly chasing each other. As discussed above, these collective “screaming parties”, together with the looping play of young birds, are central to swifts’ social, territorial, and intergenerational lives. Swifts also engage in these flying screaming parties along streets, with the houses of their cavities at the centre of their flight trajec- tories. When this house is a tower, they circle around it. It seems that a tower perfectly suits swifts’ circling patterns, possibly even enhancing the pleasure these parties provide.46 The noisy, circling flights around the rising part of the building appear to be a dazzling 44 Lestel, Origines animales. 45 It is noteworthy that in other regions the common swifts have storied their places with different cultural heritages, such as in Leiden in the Netherlands, where they nest in “the gaps under the zinc gutters in 1970s housing estates, the openings beneath the roof tiles of the seventeenth-century church and between the bricks of the old wind- mill” (Schilthuizen, Darwin Comes to Town, 75). 46 Ornithologists presume that play may be a factor in these flights (Genton and Jacquat, Mar- tinet noir, 89) and I can also easily imagine the pleasure of speed afforded by these circles. d’Hoop, Crossing Worlds | 71 Humanimalia 14.1 (2023) performance for those partaking and for those observing. The swifts’ acrobatic flight is a recurrent fascination among scientists and enthusiasts. Their social choreographies awaken a sense of grace with their aerial slides, the agility of their dives and bounces, and the thrill of excitement while pursuing each other. As philoso- pher Etienne Souriau contends, these aesthetic movements are not simply instinctive and mechanical repetitions. When animals play with their driving forces and try to find the right rhythm, their sen- sitivity is at stake.47 Hence, such aesthetic experiences do not hap- pen just for the appreciative observer, but for the aerobatic birds as well. I would add that the possibility of an aesthetic encounter also involves the towers that mediate the birds’ circling movements and their captivating expression. Such spectacles have been a common sight in northern Italy for cen- turies. The use of “swift towers” (“torri rondonare” in Italian) most probably spread among medieval fortified buildings from the fif- teenth century, possibly even the thirteenth century, onwards. As Mauro Ferri describes, artificial nests were installed in tower houses (“casa torre”), and then in belfries, farmhouses, palaces, bell towers, and so on. Up until the twentieth century, turrets were also added on existing roofs. They were made of rows of cells embedded in walls, which the birds could reach through little corridors. The rows of holes added regular touches to the sober architecture (fig. 8). At the back of each cell, a wooden plug could be removed in order to capture nestlings before their first flight, once they were fattened and would taste like “small butter pancakes”.48 Young swifts were cooked, canned, and stored for gastronomic occasions or offered as highly valued gifts. The delicacy was rare, since the selection of nest- lings had to be carefully carried out, on the condition that the cap- tures would not harm the colonies. Ferri found regional variations for coping with that condition: either the first brood was completely spared, or only one bird was taken; or else, for each brood, “one chick had to be spared so that the parents were not upset”.49 The 47 Souriau, Le Sens artistique, 27–58. 48 Ferri, “Ancient Artificial Nests”, 231. 49 Ferri, 235. Fig. 8: The swift tower of Castellaro, Italy. Photograph by Martine Wauters. Used with permission. d’Hoop, Crossing Worlds | 73 Humanimalia 14.1 (2023) birds’ breeding places were thus a means for exploiting their chicks as food and involved moral obligations within a strongly asymmet- rical relationship. Whereas swifts were offered shelter at the expense of (a part of) their progeny, humans got a delicious dish with little in- convenience. Nowadays, hundreds of these towers are still stand- ing but left in ruins since the practice faded in the early twentieth century, as little birds were not considered food anymore. Ferri has been fighting to preserve this heritage, which he thinks may be re- discovered to support the species, along with the novel “swift tow- ers” that have recently mushroomed across Europe.50 Back to Brussels, and for those like Martine who have witnessed swifts’ screaming parties around Italian towers, watching the city “with swifts’ eyes” also means that towers spark the imagination. She now notices certain towers in the city that emerge as good candi- dates for future transformation. She has integrated nest boxes in some of them located in schools, churches, or in industrial build- ings such as a former brewery, in an effort to match the architec- tural style of the towers. The success of these operations depends on swifts adopting the next box, circling around it, and amplifying its aesthetic. However, this is not always easy, as with the Tomb- erg tower in eastern Brussels. This tower was part of a municipality building listed for its 1930s Art Deco style. At a time when its resto- ration was planned, Martine had already spotted that tower and got ideas from the Italian swift spectacles. She joined meetings to pro- pose swift boxes for the design project. First approved by the mu- nicipality, the Historic Monuments and Sites Department, the ar- chitect and the contractor, the boxes were later excluded from the project due to overwhelming concerns about finding the right aes- thetic style in harmony with local heritage. Here the concern about the exclusive conservation of an architectural heritage dispelled the possibility of an aesthetic multispecies encounter. 50 “Swift towers” are installations erected in the past few years, sometimes standing as artworks. Although swifts devote a lifelong (and generation-long) faithfulness to their nesting territory, these installations appear far less permanent than towers belonging to buildings. 74 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) Yet, a change is underway: today putlog holes and (certain kinds of) towers compel attention because they are at the crossroads of swifts’ and human cultural heritage. While the former called to swifts’ in- genious agency in converting an architectural artefact into a home, the latter started as a technology for food exploitation and persists as an architectural artefact that intensifies the encounter through the pleasures of joyful circles around rising brickwork. Ultimately, en- gaging with swifts’ meaningful connections with putlog holes and towers involves the possible reactivation of these technical and aes- thetic heritages. Risky Nest Boxes Lastly, a great deal of Martine’s interventions to install nest boxes con- sists of going up to rooftops via scaffolding or a lift, sometimes with the support of the municipality. The placement of artificial nest boxes, and their possible adoption by swifts, is a widespread practice across Europe. For the human novices who discover them, the nest boxes appear as devices through which forms of proximity with birds are in- vented. The making of artificial nests for swifts includes the deploy- ment of many technical details that adapt the boxes to their needs, for instance, by using thermos-regulator materials, designing a slant- ing roof that prevents predators from landing, an entrance that dis- courages other dwellers, or by inserting a cup in the nesting area that spares them time in building a whole nest (Fig. 9 a & b). Yet, for swifts to adopt new nesting sites, installing boxes is only the first step. Once the boxes have been correctly installed (e.g. at a suffi- cient height, avoiding the threat of overheating due to a south-west- erly orientation, at irregular intervals to prevent swifts from mistak- ing “their” entrance and the ensuing fights, etc.), further effort is required to lure the birds to them. It typically takes years before swifts select a box and make it their home, so recordings of their vo- calizations are used to attract them.51 As such, nest boxes cannot be 51 Monitoring studies that report adoptions of nest boxes placed as compensatory meas- ures in the context of building transformations remain scarce and ambiguous. Two Ger- man investigations show contrasting results: the first one accounts an occupation of ten per cent of the boxes by swifts, and the second more optimistically reports that twenty Fig. 9: a) Four nest boxes installed by an inhabitant in Brussels. b) Close-up of a nest box. Note the three lines carved under the hole to enable swifts to grip the box before entering. Photographs by the author, with thanks to Nick Winship. 76 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) reduced to the mere solution of installing and improving a technol- ogy in itself. The boxes require ongoing attention and care, therefore more volunteers, and more of their patience and stamina. Artificial nest boxes offer the promise of rejoicing when catching a glimpse of a swift flying towards the hole, but this is not guaranteed. The suc- cess of these nest boxes is a risky affair: it requires the refinement of these technologies to make them more inviting to the birds, the cre- ation of a “fictional presence” of swifts using sound, and the boxes must be watched over while letting swifts choose whether to re- spond to those tricks. But installing nest boxes runs greater risks than being seen as solu- tions in themselves and forgotten about after being placed. Martine told me a story with some unease, in which she evoked the con- struction of a huge package distribution centre on a vast wasteland of twelve hectares along the Brussels canal. From 1930 to 1993, the site was host to a gas plant that produced and delivered town gas, coke, and derived products for the carbon-chemical industry. As a result, it was estimated to be the most polluted site in the Brussels region.52 Like many former industrial sites, in the decades since the plant closed down, the area had become a marsh where many ani- mals and plants had come to dwell. The wasteland was quite famous among Brussels’ naturalists. For birds alone, they reported about sixty different species living on the site, both endemic and migratory. In order to compensate for the loss of habitat, the company pro- posed to install eight nest boxes for swifts, but without much care about how it would be done. In short, placing the boxes provided an alibi for a cynical greenwashing operation. Following a public in- quiry, environmental organizations lodged objections during the au- thorization procedures, but without going to court. An ambivalence pervades Martine’s account: like other environmen- talists, she sorely regrets the loss of the wasteland, but since the mega-depot was going ahead with its eight nest boxes anyway, she four per cent of boxes placed during renovation were occupied thereafter (Schaub, Mef- fert and Kerth, “Nest-boxes for Common Swifts”). 52 IBGE, Rapport sur l’état de l’environnement. d’Hoop, Crossing Worlds | 77 Humanimalia 14.1 (2023) provided advice on how to better integrate them so that swifts could actually adopt them. Again, what was at stake for her was the con- veying of importance. The negotiation opened a big door for her to become an advisor for Citydev, a public organization that plays a cen- tral role in the development of real estate housing projects and busi- nesses across the city. There is a success for Martine and the swifts here: the increasing importance of integrated nest boxes through- out the city. However, I cannot help but see a contradiction in the use of the nest boxes for the construction on the wasteland. Placing the boxes requires few engagements: they are not expensive, do not bother the human residents, and may give the construction project an unearned positive image. In other words, since swifts are unob- trusive dwellers in human buildings, interventions to install nesting sites may help to justify construction projects and draw attention away from the way these projects destroy other living beings’ places. With cautious use, the boxes are technologies that create proxim- ity and meaningful possibilities for the birds, but these objects are also dangerous since they can be easily mobilized as instruments for greenwashing. Watching the City “with Swifts’ Eyes” Once “we” have met, we can never be “the same” again. Propelled by the tasty but risky obligation of curiosity among companion species, once we know, we cannot not know. If we know well, searching with fingery eyes, we care. That is how responsibility grows. — Donna Haraway, When Species Meet In their storying of places, swifts have an astute knowledge of our buildings that illuminates a world made of generational transmis- sions, scream dialects and looping parties, flight attunements to par- ticular entrances, hole arrangements, and fierce fights. These dwell- ing practices involve the social creation of distinctive places. What is it, then, to engage with storied places, with swifts’ meaningful 78 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) neighbourhoods, buildings, and holes? What does it mean to care in this case? I conclude by coming back to the expression “watching [the city] with swifts’ eyes”. Of course, it is impossible for us to fully grasp the experiential world of other animal subjects. The expres- sion “with swifts’ eyes” does not imply putting or imagining oneself in the birds’ place. It rather signals a practice of attentiveness and imagination that experiments with a proximity to the bird, by pay- ing attention to what matters or could matter to them in the shared environment. How does this attentiveness take shape along with the transformation of buildings? Which tensions or contradictions emerge in their wake? Perhaps the most striking occurrences that call attention are swifts’ “screaming parties”, during which they pursue each other over their territory. While first hearing these screams and then recognizing them, these parties draw swift lovers to notice the birds’ particu- lar neighbourhoods and nesting places. Without such opportuni- ties, it is rare to notice one of them entering a hole. Swifts’ sounds are thus crucial to further scrutinize small crevices in walls and eaves, both for the members of a colony and for their human en- thusiasts. From there, Martine’s attention enlarges through an ac- cumulation of local observations. Not only swifts’ stubborn fidelity to their nesting sites leads her to return each spring to these same places, anticipating the joy of finding migrators again, but she also learns from other connoisseurs what the architectural preferences of these birds may be, and becomes more aware of them. In this way, specific historical artefacts, like putlog holes or historic tow- ers, compel attention and hold aesthetic appeal. They call to reac- tivate these otherwise forgotten inheritances with which the birds have woven their world for centuries, despite the prevalence of hu- man-centred aesthetics in architecture. Swift caretakers are also drawn into their world when refining nest-box technologies to craft better scenarios for them. These boxes demand a surplus of atten- tiveness, like when using playbacks of swifts’ calls in the hope of attracting them. Yet, they can easily be turned into compensation instruments that justify destruction. d’Hoop, Crossing Worlds | 79 Humanimalia 14.1 (2023) In addition, the practice of engaging with swifts’ storying of places implies the sparking and stretching of imagination. The expression “watching [the city] with swifts’ eyes” signals how that practice of attention involves imagination, like when spotting old towers and starting to see the promise of circling parades and their aesthetic pleasures. I pinpoint this imaginative work, too, when Martine sug- gests their “fictional presence”. This consists of conveying impor- tance to interlocutors previously ignorant of swifts, by mimicking the birds’ movement during a meeting, showing objects, or through oral descriptions in situ; when Martine mimics the swifts’ calls in a way that plays into their quest for sociability; or when sharing anec- dotes or videos on her blog. The attentiveness in the care for swifts is intimately bound up with these acts of imagination. These ways of paying attention and of stretching the imagination belong to a form of care through which swifts and humans come to be with each other, in meaningful ways, through material inter- faces of buildings such as holes, eaves, nest boxes, house blocks, putlog holes, or certain kinds of towers. Rather than a co-becoming through bodily co-presence and touch, the relating through which these species constitute each other is mediated by those specific ar- chitectural interfaces. As these buildings and their material invita- tions have long attracted swifts in human-made cities, today they appeal to human caregivers and their abilities to respond to swifts’ storied places through their ears, eyes, mimicry, imagination, and reshaping of the built environment. In this way, these buildings lure both swifts and humans to cross each other’s worlds. It is through such attentive and imaginative practices that material interventions with a fuller appreciation of swifts’ meaningful worlds emerge, and will most likely spread. 80 | d’Hoop, Crossing Worlds Humanimalia 14.1 (2023) Acknowledgements I am deeply grateful to Martine Wauters; this article could not have been researched if she had not generously welcomed me into her impressive practice dedicated to swifts’ fate. Thank you as well to Mélanie Tamm for sharing with me her knowledge about putlog holes, and to Alain Boeckx and Steyn Van Assche for sharing theirs about the Cokerie du Marly wasteland. For allowing me to publish their pictures, thank you to Luca de Carli, Elizabeth Thornburn, Mark Pearse, Brigitte De Boeck, Jean-Claude Hardy, Nick Winship, and again to Martine Wauters. 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