ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah Acta Herpetologica 7(1): 171-174, 2012 Scavenging in the genus Natrix Cesar Ayres Ashega. Barcelona 86, 6ºC. 36211, Vigo (Pontevedra), Spain. E-mail: cesar@herpetologica.org Submitted on: 2011, 17th December; revided on: 2012, 30th January; accepted on: 2012, 15th February. Abstract. Scavenging is reported as an unusual behaviour of snakes. However, it is likely more common than is supposed. Here I report the use of dead newts as prey source by water snakes of the genus Natrix at a dam in north-western Spain. Juve- niles and adults viperine snakes (Natrix maura), and also an adult grass snake (Natrix natrix) were found feeding on newt carcasses. Keywords. Scravenging, Natrix, Spain. Scavenging in wild snakes has been widely ignored or is barely known, even though there are many references describing this behaviour (see references in DeVault and Kroch- mal, 2002). From older reports (Cowles, 1946) to the most recent ones (Platt and Rainwa- ter, 2011; Lillywhite and Brischoux, 2011) the number of species observed scavenging has increased, involving pitvipers (Lillywhite et al., 2008) and piscivorous species more fre- quently than other species (DeVault and Krochmal, 2002). The use of carrion as a food resource could be difficult to evaluate using traditional methods, as stomach contents analysis, unless prey items present signs of decomposition or contain fly larvae. Most of the references originates from accidental observations, some from road-killed preys (Mora, 1999; Phelps, 2006; Ventura, 2012). It has been also related with cannibalistic behaviour in some cases (Lillywhite, 1982). During the monitoring of a mass-mortality of amphibians in a small reservoir close to Pontevedra (42.29º N, 8.36º W Spain), I have observed several scavenging events by water snakes (genus Natrix). The first one was detected on April 26th 2011 (Ayres, 2012); a juve- nile viperine snake (Natrix maura) was detected while trying to ingest a dead individual of Bosca´s newt (Lissotriton boscai). On May 23th and 30th 2011 four N. maura individuals were found dead without symptoms of predation or illness, three juveniles and one adult, all of them had ingested dead L. boscai with symptoms of decomposition. On May 2nd a grass snake (Natrix natrix) was detected on the shore of the reservoir lake, over dried aquatic vegetation. The snake was actively searching under the vegeta- tion by tongue flicking and quick head movements. A couple of minutes later the head of 172 C. Ayres the N. natrix disappeared under the vegetation, and subsequently reappeared with a dead newt in its mouth (Fig. 1). This behaviour is consistent with previous findings of Sazima and Strüssman (1990) and DeValt and Krochmal (2002). These authors suggest that carrion consumption could be influenced by behavioural processes. Species that use chemical cues to find their prey and semi-aquatic or aquatic species scavenge more frequently than species that used vis- ual cues. Sazima and Strüssmann (1990) suggested that carrion aggregation by water cur- rents increases the probability of detection, also influenced by chemical gradients that give more directional information in water. Importance of chemical cues in the behaviour of scavenging has been studied in detail on the brown tree snake (Boiga irregularis) by Shivik and Clark (1997) and Shivik (1998, 1999). These authors demonstrated that B. irregularis is able to find carrion using only chemical cues, but the brown tree snake needs a combination of chemical and visual cues to capture live prey. Consumption of carrion was described for N. natrix by Poschadel and Kirschey (2002). Scavenging was not described for N. maura, although Hailey and Davies (1986) reported that exploratory activities and cruising could be use to find dead preys. But recent findings (Ayres, 2012) confirm that both species can use carrion as a food resource. Even more, juvenile viperine snakes have been observed to feed on caned sardines used as bait (Ayres, pers. obs.). As a conclusion, it seems that scavenging behaviour in snakes is more common than it was supposed previously, just often overlooked or simply not observed. Some species Fig. 1. Adult grass snake with a dead newt in its mouth. 173Scavenging in the genus Natrix use carrion consumption as an adaptation to a specific habitat (i.e., insular isolation; Lilly- white et al., 2002, 2008). Carrion consumption by Florida cottonmouths (Agkistrodon pis- civorus conanti) living in Seahorse Key has been studied in detail. This snake population depends mostly on fish that are dropped or regurgitated by colonial wading birds that nest on the island (Lillywhite et al., 2002, 2008). These authors also suggested that it could be part of an “island syndrome” which implies behavioral and physiological modifications as a response to resource limitations on islands. Other species could use carrion as an opportunistic food resource, like the described episode. The absence of more reports could be due to the inconspicuous life of many snake species, including rarely seen feeding behaviour. ACKNOWLEDgEMENtS Konrad Mebert and an anonymous reviewer provided valuable comments and suggestions that improved this note. REFERENCES Ayres, C. (2012): Natrix maura (Viperine snake): Diet. Herp. Rev. (in press) Cowles, R. B. (1946): Carrion eating by a snake. Herpetologica 3: 121-122. DeVault, t.L., Krochmal, A.R. (2002): Scavenging by snakes: an examination of the litera- ture. Herpetologica 58: 429-436. Hailey, A., Davies, P.M.C. (1986): Diet and foraging behaviour of  Natrix maura.  Herpetol. J. 1: 53-61. Lillywhite, H. (1982): Cannibalistic carrion ingestion by the rattlesnake, Crotalus viridis. J. Herpetol. 16: 95. Lillywhite, H.B., Sheehy III, C.M., McCue, M. (2002): Scavenging behaviors of cotton- mouth snakes at island bird rookeries. Herp. Rev. 33: 259-261. Lillywhite, H.B., Sheehy III, C.M., Zaidan III, F. (2008): Pitviper scavenging at the inter- tidal zone: An evolutionary scenario for invasion of the sea. BioScience 58: 947-955. Lillywhite, H.B., Brischoux, F. (2011): Is it better in the moonlight? Nocturnal activ- ity of insular cottonmouth snakes increases with lunar light levels. J. Zool. Lond.: doi 10.1111/j.1469-7998.2011.00866.x Mora, J.M. (1999): Leptodeira annulata (Culebra Destenida, Banded Cat-eyed Snake): Diet. Herp. Rev. 30: 102. Phelps, t. (2006): Naja nivea (Linnaeus, 1758) Cape cobra. Scavenging. African Herp News 40: 24. Platt, S.g., Rainwater, t.R. (2011): An observation of scavenging by Crotalus molossus (Baird and girard, 1853). J. Kansas Herpetol. 37: 8-9. Poschadel, J., Kirschey, t. (2002): Aasfressen bei der Ringelnatter (Natrix n. natrix).    Z. Feldherpetol. 9: 223-226. Sazima, I., Strussmann, C. (1990): Necrofagia em serpentes brasileiras: exemplos e previ- soes. Rev. Bras. Biol. 50: 463-468. 174 C. Ayres Shivik, J. A. (1998): Brown tree snake response to visual and olfactory cues. J. Wildlife Manage. 62: 105-111. Shivik, J.A. (1999): Carrion, context, and lure development: the relative importance of sensory modalities to foraging brown treesnakes (Boiga irregularis). Ph.D. Disserta- tion, Colorado State University, Fort Collins, Colorado, U.S.A. Shivik, J.A., Clark, L. (1997): Carrion seeking in brown tree snakes: importance of olfac- tory and visual cues. J. Exp. Zool. 279: 549-553. Ventura, F. (2012): Comportamiento carroñero en Malpolon monspessulanus. Bol. Asoc. Esp. 23 (in press).