Avian Scavengers, but Not Conspecifics, Feeding on the Carcasses of Storm-Killed Turkey Vultures on the Falkland Islands
Total Page：16
File Type：pdf, Size：1020Kb
Vulture News 67 November 2014 vember 2013 Avian scavengers, but not conspecifics, feeding on the carcasses of storm-killed Turkey Vultures on the Falkland Islands Keith L. Bildstein1*, Micky Reeves2, Melissa M. Bobowski1 and Anna R. Autilio3 1Acopian Center for Conservation Learning, Hawk Mountain Sanctuary, 410 Summer Valley Road, Orwigsburg, PA 17961, USA. 2 Falklands Conservation, Jubilee Villas, Stanley, Falkland Islands. 3 Department of Biology, Boise State University, Boise, ID 83725, USA. *Corresponding author: [email protected] Introduction Fernandez-Arroyo (2001); two young Griffon Vultures feeding on the Cannibalism, which the Shorter carcass of a conspecific in an area Oxford English Dictionary defines as where poisoning had occurred “an animal that eats members of its (Camiña et al. 2002); and several own species” (Trumball & Stevenson Griffon Vultures pecking at, and 2002), is quite common among birds subsequently killing and eating, a of prey. However, it is thought to be conspecific that was trapped under a rare among both Old and New world rock while feeding on a sheep carcass vultures (Mundy et al. 1992, Clinton- (Martinez de Lecea 2011). In Africa, Eitniear & McGehee 1994). Mundy et al. (1992) report Gyps Examples of cannibalism from Spain vultures feeding on an African White- include an ambulatory nestling backed Vulture (G. africanus) that Griffon Vulture (Gyps fulvus) feeding had been “caught by the wing in an upon an adult (presumably its dead elephant’s carcass and had died, or parent) at a nest (Fernandez & was killed, at the spot and eaten there by other vultures.” They also mention 53 Vulture News 67 November 2014 vember 2013 a report of Cape Vultures (G. species of avian scavengers on two coprotheres) feeding on a conspecific apparently storm-killed Turkey without additional detail. And a Vultures on Saunders Island, in the parent Bearded Vulture (Gypaetus Falkland Islands, in July-August barbatus), a species known to exhibit (austral winter) 2014. siblicide, was observed feeding the remains of a younger chick to its Observations sibling at a nest in northeastern Spain (Margalida 2004). Observations were made between 30 Examples of cannibalism among July and 7 August 2014, on Saunders New World vultures include several Island, a 12,500ha island off the north events involving captive King coast of West Falkland in the south Vultures (Sarcoramphus papa) in Atlantic, approximately 400 km from zoos, and a possible instance the South American mainland. The involving free-ranging Lesser island, which is treeless Patagonia Yellow-headed Vultures (Cathartes Steppe and has a permanent human burrovianus) at a road-kill in population of five, functions as a Tabasco, Mexico (Clinton-Eitniear & sheep farm and tourist destination for McGehee 1994). Importantly, Snyder nature photographers. Four species and Snyder (2000) report that placing of penguins and other seabirds breed Turkey Vulture Cathartes aura by the thousands on Saunders, and carcasses at a vulture feeding station since 2010 we have been studying the in Florida, USA, appeared to scavenging behaviour of raptors, “strongly inhibit use of these sites” by including Turkey Vultures, feeding at other vultures. And in coastal and around a large colony of Gentoo Veracruz, Mexico, where a flight of Penguins (Pygoscelis papua) at “The approximately three million Turkey Neck,” in the northwestern part of the Vultures passes each autumn and a island. Our study site, at somewhat smaller flight passes each approximately 51° south, experiences spring, Turkey Vultures that die in the a cool seasonal oceanic climate with region are not eaten by other Turkey largely westerly winds that can be Vultures (Lowery & Dalquest 1951). quite strong. Temperatures on the Here we report on the feeding Falklands generally range from behaviour, and lack thereof, of three maximum highs of 25° C in austral 54 Vulture News 67 November 2014 vember 2013 summer to minimum lows of -11° C juvenile Striated Caracaras in winter, with monthly temperatures (Phalcoboenus australis), all of averaging 9° C in austral summer and which were standing on the ground. 2° C in austral winter. Snow falls, Five adult Turkey Vultures, one of usually in small amounts, on about 55 which was standing and four of which days of the year, with most snow were flying, also were observed. melting within 48 hours (Strange None of the standing birds were 1983). within 100 m of the two carcasses, An unusual snowfall of more than but two of the flying Turkey Vultures 10 cm fell on 24 and 25 July several were spotted passing directly days in advance of our visit and it, overhead, flying at less than 20 m together with low temperatures that above the dead birds. KB next reached -10° C during the nights of visited the study site in early 26-27 July delayed our first visit to afternoon on 1 August and recorded “The Neck,” which is 16 km over 22 mainly juvenile Striated Caracaras rough terrain from our base camp on along with two adult Southern the island, by four days. An initial Crested Caracaras (Caracara visit on 31 July by one of us (KB) plancus), all of which were standing, found the carcasses of two Turkey as well as four adult Turkey Vultures, Vultures, one of which was headless, all of which were flying low over the at the site. The bodies, which were site during the course of a one-hour about 20 m apart on a 2km-long survey. Three of the juvenile sandy beach, were mixed in amongst caracaras were feeding on one of the a heavy drift line of kelp and other Turkey Vulture carcasses, which was seaweed, and most likely the birds headless and lying on its back, and had died during the recent snow whose body cavity had been broken storm at a roost site in a small grove into (Figure 1). Two of the flying of Monterey cypress (Cupressus Turkey Vultures passed within 20 m macrocarpa) 150 m from where the of the carcasses but did not deviate carcasses were found. from their flight while passing over Over the course of an hour of the bodies and thereafter continued population-survey work at mid-day flying out of sight. on the 31st, KB recorded 27 mainly 55 Vulture News 67 November 2014 vember 2013 Figure 1: The first opened Turkey Vulture carcass on 1 August 2014. Three of us (MR, MB, & AA) visited KB again surveyed the site at the study site on 2-5 August and saw mid-day on 5 August and recorded 27 a single Striated Caracara feeding on mainly juvenile Striated Caracaras the first opened carcass on the during a survey of scavengers at the morning of 3 August. We also saw site, all of which were standing, two juvenile Striated Caracaras and together with one adult male dark- an adult Turkey Vulture feeding on morph Red-backed Hawk (Buteo an Imperial Shag (Leucocarbo polyosoma) that was feeding on the atriceps) we had discovered that day first carcass that had been broken into less than 50 m from the closest (Figure 2). When first encountered Turkey Vulture carcass. We also the hawk was being harassed by three noted that both Turkey Vulture juvenile Striated Caracaras, one of carcasses had been opened and fed which briefly hovered less than 0.5 m upon by 4 August. above the hawk before striking it on 56 Vulture News 67 November 2014 vember 2013 the head with clenched talons and Caracaras in pursuit. After the hawk then re-landing 2 m away. After departed several Striated Caracaras fewer than 2 min of direct approached the carcass and began observations from a distance of feeding upon it. No Turkey Vultures approximately 5 m, the hawk flew off were seen at the site during the 50- with a gorged crop with two Striated min survey. Figure 2:. The first opened carcass being fed upon by a Red-backed Hawk on 5 August 2014. Note the three Striated Caracaras looking on. A final brief visit at mid-day on 7 and four in-flight Turkey Vultures, August, shortly before we departed none of which was within 100 m of the island, found more than 20 either carcass. Striated Caracaras standing at the site 57 Vulture News 67 November 2014 vember 2013 Discussion (see references above) reluctance to cannibalize members of their own Taken as a whole, our observations species. That this occurred in the indicate little if any reluctance on the middle of winter on the Falkland part of Striated Caracaras (an obligate Islands when food availability for and opportunistically predatory scavenging birds of prey appears to scavenging bird of prey) and at least be limited and when at least one of one adult Red-backed Hawk (a the species involved, the Striated largely facultative scavenger species Caracara, is known to be food that is far less common at the site) to stressed at this time (cf. Rexer-Huber feed on one of the two available & Bildstein 2013), further supports Turkey Vulture carcasses. On the the notion of a reluctance to other hand, at least several Turkey cannibalize on the part of Turkey Vultures most likely detected the two Vultures. The reason for this remains carcasses, both unopened and opened, enigmatic. but none was seen feeding upon them, even though at least one adult Turkey Acknowledgements Vulture fed upon an Imperial Shag carcass <50 m from the vulture We thank the Pole-Evans family for carcasses. Although we were in the their outstanding hospitality on area for fewer than six hours on eight Saunders Island and the Falkland days during the course of a 9-day Islands Government for issuing the period, the apparent lack of interest permits necessary for our studies.