1 ABUNDANCE OF WINTER TICKS (DERMACENTOR ALBIPICTUS) IN TWO REGENERATING FOREST HABITATS IN NEW HAMPSHIRE, USA Brent I. Powers and Peter J. Pekins Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH 03824, USA. ABSTRACT: Recent decline in New Hampshire’s moose (Alces alces) population is attributed to sus- tained parasitism by winter ticks (Dermacentor albipictus) causing high calf mortality and reduced productivity. Location of larval winter ticks that infest moose is dictated by where adult female ticks drop from moose in April when moose preferentially forage in early regenerating forest in the northeast- ern United States. The primary objectives of this study were to: 1) measure and compare larval abun- dance in 2 types of regenerating forest (clear-cuts and partial harvest cuts), 2) measure and compare larval abundance on 2 transect types (random and high-use) within clear-cuts and partial harvests, and 3) identify the date and environmental characteristics associated with termination of larval questing. Larvae were collected on 50.5% of 589 transects; 57.5% of transects in clear-cuts and 44.3% in partial cuts. The average abundance ranged from 0.11–0.36 ticks/m2 with abundance highest (P < 0.05) in partial cuts and on high-use transects in both cut types over a 9-week period; abundance was ~2 × higher during the principal 6-week questing period prior to the first snowfall. Abundance (collection rate) was stable until the onset of < 0°C and initial snow cover (~15 cm) in late October, after which collection rose temporarily on high-use transects in partial harvests during a brief warm-up. The higher abundance of winter ticks on high-use transects indicates that random sampling underestimates tick abundance and relative risk of infestation of moose. Calculating an annual index of infestation of winter ticks on moose is theoretically possible by integrating 3 factors: the infestation of harvested moose in October, the length of the questing period, and assuming a stable collection rate during the questing period. ALCES VOL. 56: 1 – 13 (2020) Key Words: Alces alces, Dermacentor albipictus, forest habitat, infestation, moose, questing, tick abundance, winter ticks The influence of winter ticks (Derma- centor albipictus) on population dynamics of moose (Alces alces) in the northeastern United States (northeast) is well docu- mented (Musante et al. 2010, Bergeron et al. 2013, Jones et al. 2017, 2019, Ellingwood et al. 2020). The physiological impact of blood loss on moose is directly associated with infestation level of winter ticks (Mu- sante et al. 2007), and recent research has addressed the physiology, ecology, and eti- ology of winter ticks (e.g., Yoder et al. 2016, 2017a, 2017b, Holmes et al. 2018). Further, the presumed influence of climate change in the winter tick-moose relationship is that longer autumns and later onset of winter weather will extend the questing period of winter ticks (Dunfey-Ball 2017, Jones et al. 2019). Potential outcomes would include higher infestation levels, more frequent epizootics (>50% calf mortality), reduced productivity in yearling and adult cows, and sustained tick abundance on the land- scape (Musante et al. 2010, Bergeron and Pekins 2014, Healy et al. 2018, 2020, Jones et al. 2017, 2019). However, few studies WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS ALCES VOL. 56, 2020 2 have attempted to measure field abundance of winter ticks (Drew and Samuel 1985, Aalangdong 1994, Addison et al. 2016), with only a single study in the northeast (Bergeron and Pekins 2014). As in typical host-parasite relation- ships, host density is directly related to parasite density with several studies in- dicating that increased moose density increases tick distribution and relative abundance (Blyth 1995, Pybus 1999, Sam- uel 2007, Bergeron and Pekins 2014). Field studies indicate that 85% of adult winter ticks are located within 60 cm of a moose carcass (Drew and Samuel 1985, 1986), and >95% of larvae are typically found within 1–2 m of the hatching loca- tion (Drew and Samuel 1985, 1986, Ad- dison et al. 2016) and ascend proximal vegetation the following autumn to quest for a host (Drew and Samuel 1985). Like- wise, in laboratory conditions Yoder et al. (2016) found that larval ticks have limited mobility, crawling only ~1 m. Recruitment of larval ticks is higher in open habitat than closed-canopy deciduous forest, ex- cept in hot and dry conditions (Addison et al. 2016). Therefore, distribution and questing location of winter ticks is where adult ticks drop from moose in March- April, and the relative infestation risk is a function of environmental conditions and habitat use by moose. Moose preferentially use young, re- generating forest habitat (4–16 years old) more than other cover types in spring and autumn (Scarpitti et al. 2005, Healy et al. 2018). Further, the same animals demon- strate overlap in use of specific cuts during spring and autumn, suggesting a positive feedback loop of infestation (Healy et al. 2018). In the single field study conducted in the northeast, larval abundance in clear- cuts was generally related to moose den- sity, but varied among and within clear-cuts (Bergeron and Pekins 2014). It is presumed that relative tick abundance is related to the previous years’ infestation level, and this earlier study was not preceded by or fol- lowed by an identified epizootic. This study was designed to measure larval abundance during autumnal questing in preferred cut habitat when tick abundance was presum- ably high following an epizootic in spring 2018 (61% calf mortality; Powers 2019). STUDY AREA The study area was in Jericho State Park located in the town of Berlin entirely within Wildlife Management Unit (WMU) C1 covering ~70 km2 in eastern Coos County in northern New Hampshire (UTM 19 T 320970 E, 4926474 N; map in Jones et al. 2017). Moose density was estimated at 0.46– 0.87 moose/km2, down from 1.2 moose/km2 in 1998 (NHFG 2015). Year-round access was through a network of former logging roads and off-highway recreational vehicle (OHRV)/snowmobile trails. The landscape was mostly lowland valleys with rolling hills and small water features (streams, riv- ers, ponds) scattered throughout. The pre- dominant cover type was northern hardwood forest consisting of American beech (Fagus grandifolia), sugar maple (Acer saccharum), and paper and yellow birch (Betula papyr- ifera and B. allegheniensis). Conifer cover in low elevation areas consisted mostly of northern white cedar (Thuja occidentalis), black spruce (Picea mariana), red spruce (P. rubens), and balsam fir (Abies balsamea); high elevation stands were red spruce and balsam fir (DeGraaf et al. 1992). The larger geographical area was the focus of a com- prehensive moose habitat and survival study in 2002–2005 (Scarpitti et al. 2005, Mu- sante et al. 2010), related studies of winter ticks and forest regeneration (Bergeron et al. 2011, Bergeron and Pekins 2014), and since 2014, survival and productivity of moose ALCES VOL. 56, 2020 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS 3 (Jones et al. 2017, 2019, Dunfey-Ball 2017, Healy et al. 2018, Ellingwood et al. 2019). METHODS Study plots were established in summer 2018 to measure larval abundance during the questing period in autumn 2018 (September– November). Plots were established in two cut types: clear-cuts (n = 22) and partial harvests (e.g., geometric thinning) (n = 22) (Fig. 1 and 2). Each was within an age range associated with preferred foraging habitat (4–10 years), 4.04–4.85 ha in size, and with ample sign of moose use. Moose use this area year-round and multiple radio-collared calves succumbed to infestation of winter ticks in springs 2014–2018. Epizootic con- ditions occurred in the larger study area in spring 2018 (61% calf mortality) and 4 of the previous 5 years (Jones et al. 2019). Two treatments were defined in each plot: 1) random area within the plot ( similar to Bergeron and Pekins 2014), and 2) high- use areas that reflected concentrated moose activity. High-use areas were obvious forag- ing sites and movement corridors on trails and edges proximate to uncut forest that were readily identified from visual inspection and evidence of browsing (Fig. 1 and 2). Each plot was sampled at least 12 times 10 m Fig. 1. Schematic illustrating the sampling design in partial harvest plots in Berlin, New Hampshire, USA. Partial harvests leave a mix of cut and uncut areas that create proximal foraging and bedding areas for moose. Green clouds depict uncut portions of trees (canopy cover) and black lines depict cut area and skid trails that serve as pathways and foraging sites. Orange lines depict typical location of high-use transects set within cut areas and skid trails. Blue lines depict typical random transects avoiding high-use areas and spaced 10 m apart. WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS ALCES VOL. 56, 2020 4 during the questing period (mid-September through mid-November); sampling contin- ued until collection of larvae ceased. Line transects were established weeks prior to sampling after visual inspections of each plot to identify random and high-use sampling locations within each plot. Tran- sects were spaced at least 10 m apart and no repeat sampling occurred of a transect either daily or during a subsequent visit. Plots were sampled bi-weekly by flagging at least 4 tran- sects (2 random, 2 high-use) per visit. Flagging followed the basic technique used by others (Drew and Samuel 1985, Piesman et al. 1986, Ginsberg and Ewing 1989, Aalongdong 1994, Bergeron and Pekins 2014) in which a 1 m2 cotton cloth was dragged over vegetation to collect questing larvae. Each transect flag was bagged (plastic ziplock) separately and frozen. Subsequently, an entire count of larvae on each flag was performed to calculate abundance (ticks/m2; area = transect length (m) × 1 m2). A subset of plots (4 clear-cut and 4 partial harvest) were monitored continuously with remote data-loggers that measured hourly am- bient temperature (±0.5ºC) from mid- August until late November at the typical questing height (125 cm) of larvae ( McPherson et al. 2000). These data were analyzed relative to collection rate and tick abundance to in- vestigate relationships between tempera- ture, tick abundance, and relative questing activity. Snow events were also monitored given the susceptibility of larvae to freezing/ desiccation (Drew and Samuel 1985). ANALYSIS The raw data exhibited the typical field-sampling problem of “zero-inflated” 10 m Fig. 2. Schematic illustrating the sampling design in clear-cut plots in Berlin, New Hampshire, USA. The clear-cut is white and set within a green cloud of unharvested forest; skid trails are depicted with black lines. Orange lines depict high-use transects placed within foraging and movement pathways (e.g., edges and skid trails). Blue lines depict random transects spaced 10 m apart through the uniform regenerating forest. ALCES VOL. 56, 2020 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS 5 data, as ~50% of transects were tick-less (i.e., negative transects); therefore, the data were analyzed using a hurdle or “two-stage” linear model. The first stage was a logistic model that used the binary form of all tran- sect data including negative transects; data were not log-transformed. In the second stage, the negative transects were removed and only positive transects were analyzed. After testing for normality, these data were subsequently log-transformed to fit a normal distribution. Both were used to test if larval abundance was different between clear-cuts and partial harvests, and between random and high-use transects within cuts. A temporal analysis of larval abundance using all transect data, ambient temperature, and questing activity was performed with a linear mixed-effects model. Fixed variables in the model included ambient temperature, transect type, date, snow depth, with plots as the random effect variable; analysis was per- formed in Program R (ver. 3.4.4, Austria). Basic summary statistics were used to ex- press and analyze ambient temperature mea- surements. The average daily temperature and abundance data were used to analyze temporal factors possibly influencing abun- dance within the model. A t-test was used to compare ambient temperature between plot types; analysis was performed in Program R (ver. 3.4.4, Austria). RESULTS A total of 589 transects were measured in the 44 plots from 15 September–20 No- vember 2018. Transect length ranged from 28–322 m (median = 177 m) in clear-cuts and 45–322 m (median = 177 m) in partial harvests (Table 1). Larval questing had initi- ated at the start of dragging on 15 September. The absolute number of larvae collected per transect ranged from 0–2,554 larvae. For all transects combined, the absolute average and maximum abundances were always higher on high-use than random transects in both cut types, with larger differences in partial cuts; a similar trend occurred on positive transects alone that had abundances ~1.5–2.5 × higher than the overall combined averages (Table 1). The first stage model (all transects) indicated that abundance was 1.8 × times higher (P < 0.05) in partial harvests (0.24 ± 0.08 ticks/m2) than clear-cuts (0.13 ± 0.03 Table 1. Field abundance (ticks/m2) of larval ticks collected from 15 September–10 November 2018 in 22 clear-cut and 22 partial cut study plots, Berlin, New Hampshire, USA. Positive transects were those where larvae were collected. Random indicates transects that were distributed randomly within a plot. High-use indicates transects that were located in areas of concentrated moose activity (i.e., game trails and foraging areas). All transects Clear-cut (random) Clear-cut (high-use) Partial Harvest (random) Partial Harvest (high-use) # of transects 140 138 155 156 Transect length (m) 74–321 28–322 70–322 45–322 Abundance (se) 0.12 (0.02) 0.15 (0.04) 0.11 (0.03) 0.36 (0.13) Max abundance 1.90 5.52 4.04 13.45 Range (# ticks/transect) 0–459 0–975 0–527 0–2554 Positive transects # of transects 74 86 66 72 Abundance (se) 0.22 (0.04) 0.25 (0.06) 0.27 (0.23) 0.81 (0.29) Range (# ticks/transect) 1–459 1–975 1–527 1–2554 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS ALCES VOL. 56, 2020 6 ticks/m2) (Table 1). There was a strong trend (P = 0.13) toward higher abundance on high- use than random transects in both cut types. The second stage model indicated that abun- dance was 2.3 × higher (P = 0.05) in partial harvests (0.54 ± 0.35 ticks/m2) than clear- cuts (0.24 ± 0.11 ticks/m2 (Table 1). Abun- dance in clear-cuts was similar (P = 0.47) on random (0.22 ± 0.04 ticks/m2) and high-use transects (0.25 ± 0.06 ticks/m2), whereas abundance was higher (P < 0.05) on high- use (0.81 ± 0.29 ticks/m2) than random transects (0.27 ± 0.23 ticks/m2) in partial harvests (Table 1). Two drags on high-use transects in par- tial harvests (13.2 and 13.4 ticks/m2) sub- stantially elevated the mean abundance estimates in weeks 2 (1.25 ticks/m2) and 8 (0.98 ticks/m2) (Table 2). These values reflected the collection of very large clusters of larvae (identified on the flags) and could be considered outliers relative to weekly estimates; their removal would more closely align the weekly estimates (0.10 and 0.05 ticks/m2). However, these data were retained in the weekly analyses because they repre- sent important characteristics of local varia- tion in larval abundance and ecology. Weekly mean abundances were used to test for a temporal relationship because the infestation rate of moose is presum- ably correlated with the relative abundance of larvae. Because snow and low ambient temperature at the end of week 6 measur- ably reduced the collection rate (abun- dance) in week 7 (Table 2, Fig. 4), linear regression was used to determine if abun- dance was constant (i.e., slope = 0) across the first 6 weeks assuming that collection rate was mostly unaffected by weather. Further, because transect type was not re- lated to abundance in clear-cuts, the means of random and high-use transects in clear- cuts (Table 2) were averaged to produce a weekly abundance; partial harvest data were not tested because abundance differed by transect type. The slope in clear-cuts was 0.0019 (90% CI = −0.004 to 0.456) and not different than 0 (P > 0.05), indicating that weekly abundance was stable in the first 6 weeks (Fig. 3). The first stage model was rerun with the 6-week data and indicated that abun- dance was 1.7 × higher (P = 0.01) in par- tial harvests (0.25 ± 0.08 ticks/m2) than clear-cuts (0.15 ± 0.03 ticks/m2) (Table 3). Similarly, higher abundance (P = 0.02) oc- curred on high-use than random transects in partial harvests (0.36 ± 0.15 vs. 0.14± 0.05 ticks/m2) and clear-cuts (0.17 ± 0.03 vs. 0.14 Table 2. Weekly larval tick abundance (ticks/m2) from 15 September to 10 November 2018, Berlin, New Hampshire, USA. Transect type indicated by “Random” and “High-use” within both cut types. Clear-cut Random SE Clear-cut High-use SE Partial Harvest Random SE Partial Harvest High-use SE Week 1 0.21 0.11 0.12 0.04 0.03 0.01 0.17 0.15 Week 2 0.03 0.03 0.13 0.04 0.43 0.40 1.25 1.31 Week 3 0.20 0.08 0.32 0.23 0.01 0.01 0.19 0.15 Week 4 0.16 0.07 0.22 0.07 0.16 0.07 0.35 0.33 Week 5 0.01 0.01 0.09 0.06 0.03 0.02 0.24 0.11 Week 6 0.20 0.10 0.22 0.08 0.19 0.12 0.19 0.08 Week 7 0.08 0.05 0.03 0.01 0.03 0.02 0.17 0.12 Week 8 0.05 0.02 0.03 0.01 0.12 0.08 0.98 0.84 Week 9 0.03 0.02 0.00 0.00 0.00 0.00 0.03 0.03 ALCES VOL. 56, 2020 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS 7 ± 0.05 ticks/m2). Abundance was similar on random transects in both cut types (0.14 ticks/m2) (Table 3). Interestingly, the second stage of the model indicated that abundance was 1.9 × higher (P = 0.03) in partial har- vests (0.54 ± 0.16 ticks/m2) than clear-cuts (0.28 ± 0.05 ticks/m2), but transect type had no effect on abundance (P = 0.90) (Table 3). Absolute abundance on high-use transects was always higher than on random transects in both cut types (Table 2). With the onset of cold temperatures and snow in late October (week 6), abundance declined in each plot and transect type in week 7 (Fig. 4). However, a temporary in- crease in activity and collection occurred on Fig. 3. The mean weekly abundance of winter ticks in clear-cuts from 15 September–26 October 2018, Berlin, New Hampshire, USA. Each point is the weekly mean prior to the snow event on 26 October that induced substantial reduction in tick abundance. The vertical line at each point represent standard error. The dotted line represents the temporal linear relationship that indicated that abundance was stable during the 6 weeks. Table 3. The 6-week field abundance (ticks/m2) of larval ticks collected in 15 September–27 October 2018 in 22 clear-cut and 22 partial cut study plots, Berlin, NH. Random indicates that transects were distributed randomly within a plot. High-use indicates transects that were located in areas of concentrated moose activity (i.e., game trails, and foraging areas). Clear-cut (random) Clear-cut (high-use) Partial Harvest (random) Partial Harvest (high-use) # of transects 105 105 106 107 Transect length (m) 74–321 28–322 70–322 45–322 Mean abundance (se) 0.14 (0.03) 0.17 (0.03) 0.14 (0.05) 0.36 (0.15) Max abundance 1.90 5.52 4.04 13.45 Range (# ticks/transect) 0–459 0–975 0–527 0–2554 Positive transects # of transects 53 69 47 52 Abundance (se) 0.27 (0.06) 0.30 (0.08) 0.30 (0.10) 0.74 (0.29) Range (# ticks/transect) 1–459 1–975 1–527 1–2554 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS ALCES VOL. 56, 2020 8 5 November (week 8) in partial cuts when ambient temperature rose to 8.5°C; abun- dance in clear-cuts did not increase concur- rently (Table 2, Fig. 4). By 10 November (week 9, Table 2), abundance was function- ally zero based on lack of collection and the obvious (observed) inability of the few collected larvae to crawl on the flag. The onset of sustained snow cover and tempera- tures <0°C coincided with a decline in larval abundance (P < 0.05). Decline in abundance in both cut and transect type from 15 Sep- tember to 20 November was correlated with date (P = 0.002). No individual effect was found with temperature or snow depth (P > 0.05); however, a significant interac- tion effect (P = 0.03) indicated their neg- ative combined effect on abundance. The termination of questing was assumed as 10 November based on lack of collection and consistent ambient temperature <0ºC. The minimal length of the questing period was 56 days based on the sampling period (15 September– 10 November), but this is considered a conservative estimate because larvae were questing on 15 September. DISCUSSION Winter tick epizootics are typically con- sidered sporadic events (Samuel 2004) and were undocumented in the northeast until the mid-2000s (Musante et al. 2010); more re- cently, the frequency of epizootics is unprec- edented in the northeast – 5 in 6 years (Jones et al. 2019, Powers 2019, Ellingwood et al. 2020). Not surprisingly, winter tick abun- dance on the landscape is poorly understood, in part, because epizootics were infrequent or unknown, and the fieldwork associated with measuring tick abundance is labor-intensive. Similarly, little is known about the actual -15 -10 -5 0 5 10 15 20 25 Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 Wk 6 Wk 7 Wk 8 Wk 9 Te m pe ra tu re (° C) Week (15 September - 16 November) Clear-cut Par�al harvest 1s t S no w fa ll Brief warm-up Fig. 4. Average daily temperature in clear-cuts and partial harvests from 15 September–16 November 2018, Berlin, New Hampshire, USA. ALCES VOL. 56, 2020 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS 9 distribution of larval ticks on the landscape relative to the dynamic nature of multiple variables including moose density, habitat/ forest diversity, habitat use and movement patterns of moose, and micro-environmental conditions that influence tick survival. This study provides novel information about tick abundance in 2 optimal foraging habitats of moose, length of the larval questing period, and conditions that terminate questing. Although the average larval abundance on random transects in clear-cuts and partial harvests (0.12 and 0.11 ticks/m2; Table 1) was similar to that measured previously in New Hampshire (2-year average = 0.11; Bergeron and Pekins 2014), the average abundance on high-use transects was 1.4– 3.3 × higher (0.15 and 0.36 ticks/m2, re- spectively; Table 1). Further, the maximum abundance on random (1.9 ticks/m2) and high-use transects (5.52 ticks/m2) in clear- cuts (Table 1) was considerably higher than that (0.40–0.64 ticks/m2) measured a de- cade earlier, and ticks were collected in all clear-cuts whereas ~10% were without ticks in 2008–2009 (Bergeron and Pekins 2014). The average abundance was much higher in Elk Island National Park in Alberta, Canada (1.36 ticks/m2) in the year preceding a moose die-off (Aalangdong 1994, Samuel 2007), except in week 2 and week 8 in partial har- vests (Table 2). It is not clear why the abun- dance in Alberta was much higher than that measured after the spring 2018 epizootic, and why average abundance in clear-cuts in New Hampshire was relatively stable since 2008–2009 despite multiple epizootics. The data reflect the difficulty and variability as- sociated with measuring larval abundance, but also indicate that larval abundance likely increased over the past decade. Furthermore, the abundance estimates provided here and in Bergeron and Pekins (2014) should be considered conservative for a number of rea- sons. Most importantly, we have no ability to estimate the efficiency or detection probabil- ity of a single drag, but it is improbable that all larvae are collected with a single drag regardless of time of day or environmental conditions. We encourage multiple sampling of transects in future experiments to improve accuracy and abundance estimates. Predictably, larvae were not distrib- uted evenly within either cut type, as not all transects produced ticks and abundance was higher on high-use transects (Table 1). Both reflect non-random or preferred habitat use by moose, and maximum abundance al- ways occurred on high-use transects in both cut types – 13.45 ticks/m2 in partial harvests and 5.52 ticks/m2 in clear-cuts. The similar abundances on random transects in this and the previous regional study (Bergeron and Pekins 2014) indicates that random sam- pling likely underestimates tick abundance, moose-tick encounter rates, and projected infestation rates. For example, the abun- dance estimates on positive transects was ~ 2 × higher than the overall average during the principal 6 weeks of questing (Table 3). It is important to recognize that the earlier study reported a regional abundance, whereas this study was within a focal area of ~70 km2 with a moderate-high moose density expe- riencing winter tick-associated mortality (Jones et al. 2019). The effect of winter conditions on quest- ing was evident due to the combined influ- ence of temperature and weather (Drew and Samuel 1985). Specifically, overall abun- dance declined in both cut and transect types after the snowfall on 24 October (week 6; Table 2, Fig. 4). Although the exposure time at <0°C lasted 3 days (25–27 October), the warm-up on 5 November (weeks 7 and 8) and associated increase in collection rate in partial harvests reflects the resilience of winter ticks at these conditions (Holmes et al. 2018, Addison et al. 2019), particularly on high-use transects in partial harvests WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS ALCES VOL. 56, 2020 10 (Table 2). The few larvae collected in week 9 were curled and immobile, characteristics consistent with thermally stressed larvae (Holmes et. al. 2018), and were presumably collected due to their claw-like appendages. As Addison et al. (2019), we found that a short-term warmup after an initial snowfall resulted in a temporary increase in larval collection, specifically in partial har- vests, indicating that prolonged (multi-day) winter weather is necessary to terminate questing. Some larvae may have been pro- tected within insulative layers/gaps in the more complex vegetative/stand structure of partial harvests than in more open clear- cuts. Eventually, sustained below-freezing temperatures and snow cover were lethal to questing ticks in all plots. Preferential habitat use by moose is well documented in northeastern forests (Scarpitti et al. 2005, Wattles and DeStefano 2013), as is selective use of regenerating forest hab- itat during the autumn questing and spring drop-off seasons of winter ticks (Healy et al. 2018). Open, regenerating habitat presum- ably provides higher relative survival of larvae that decline in abundance and sur- vival as canopy cover exceeds 60% (Drew and Samuel 1986, Aalangdong 1994, Terry 2015, Addison et al. 2016). Abnormally dry and drought-like conditions in late summer and early autumn can measurably reduce larval survival (Dunfey-Ball 2017), but less so in closed canopy habitat (Addison et al. 2016). Partial harvests arguably provide an optimal mix of foraging (open) and bedding (canopy) habitat for moose, an optimal mix of microhabitats to sustain egg and larval abundance of winter ticks in a range of en- vironmental conditions, and subsequently, an optimal transmission nidus that sustains winter tick infestation of moose. Although a moose-tick encounter rate was not measured, the stable abundance measured throughout the questing period is potentially useful to estimate the final infes- tation (index) at the termination of questing. Infestation is measured on the shoulder and rump of harvested moose (Sine et al. 2009, Bergeron and Pekins 2014) in October in Maine, New Hampshire, and Vermont to produce an annual harvest index that is cor- related with the probability of winter tick- associated mortality of calves (Dunfey-Ball 2017). However, a stronger relationship exists between a similar index measured on January-captured calves of known fate (Ellingwood et al. 2019, Jones et al. 2019). Assuming the infestation rate is stable throughout the questing period (as reflected by the stable abundance measured here), the harvest index could be extrapolated to a final index by assuming two dates: 1) the start date of the questing period and 2) the date that questing terminates due to envi- ronmental conditions. The extrapolated final index could be substituted for the January index to better predict survival of calves, as- suming that larvae and nymphs are not mea- surably reduced by grooming prior to early January; however, this assumption may be invalid as experimentally infested (larvae) captive moose groomed throughout autumn (Addison et al. 2019). Ongoing analyses are exploring the potential accuracy and useful- ness of such an approach. The variability in tick abundance by cut and transect type not only reflects areas of lower and higher infestation risk, but also, that relative risk reflects individual differ- ences in activity, foraging behavior, and habitat use by moose. Likewise, the annual infestation on harvested moose varies con- siderably by sex and age (Samuel and Barker 1979, Drew and Samuel 1985, Bergeron and Pekins 2014), and for calves, mortality is di- rectly related to the level of individual infes- tation (Ellingwood et al. 2019). Those calves surviving in an epizootic year presumably reflect local variance in tick abundance, ALCES VOL. 56, 2020 WINTER TICK ABUNDANCE AND DISTRIBUTION – POWERS AND PEKINS 11 relative infestation risk, and individual habi- tat use within the epizootic area. Using previous larval abundance es- timates (Bergeron and Pekins 2014) in an agent-based model based upon availability of local regenerating (cut) habitat and its use by radio-collared moose, Healy et al. (2020) pre- dicted calf mortality similar to that measured in the field (Jones et al. 2019). The strong influence of preferential habitat use on infes- tation was supported by this modeling exer- cise that restricted moose-tick encounters to cut habitat that was <20% of the home range of moose. The higher larval abundances re- ported here suggest that predictions of Healey et al. (2020) were conservative and that pro- portionally small, yet high-use travel routes and foraging areas within cuts provide the nexus for high infestations on moose. Interestingly, differences in moose and tick response to clear-cuts and partial har- vests might lead to differences in the adjacent states of Maine and New Hampshire. Forest harvest regulations enacted in the 1989 State Practices Act of Maine effectively restricted size of clear-cuts in response to extensive salvage operations associated with the re- gional outbreak of spruce budworm (Chori- stoneura spp.); ironically, moose expansion in the northeast was spurred by these op- erations (Bontaites and Gustafson 1993, Wattles and DeStefano 2011, Dunfey-Ball 2017). However, timber removal has since increased not declined in Maine because the footprint of forest harvesting has expanded as partial harvests have increased >90% (MFS 2016). These harvest regulations may have increased and sustained high availabil- ity of more preferred/optimal habitat and moose density, while inadvertently increas- ing local tick abundance, infestation rate of moose, and the probability of an epizootic during warming weather and environmental conditions that simultaneously benefit win- ter ticks. 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