SEPTEMBER 2007 SHORT COMMUNICATIONS 235 J. Raptor Res. 41(3):235–238 E 2007 The Raptor Research Foundation, Inc. WHY DO CONDORS AND VULTURES EAT JUNK?: THE IMPLICATIONS FOR CONSERVATION DAVID C. HOUSTON1 Ornithology Group, Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ U.K. ALLAN MEE Zoological Society of San Diego, CRES, 2920 Zoo Drive, San Diego, CA 92101 U.S.A. MIKE MCGRADY Natural Research Ltd., Am Rosenhu¨ gel 59, A-3500 Krems, Austria KEY WORDS: vulture; condor; conservation; diet; junk; trash. fulvus) at the Gamla Golan Heights colony. Most nests The seven species of New World condors and vultures are strewn with junk; such quantities have been found in and the 15 species of Old World vultures are taxonomically the stomach of chicks that it can easily be felt, and heard, unrelated, being descended from ancestral storks and ea- by gently palpating the stomach, and this condition has led gles, respectively (Feduccia 1996). They occupy identical to at least one known gut blockage: (Ferro 2002, B. Wood- scavenging roles in their respective ecosystems, being clas- ley and O. Bahat pers. comm.). In Armenia, a griffon vul- sic examples of convergent evolution. Species specialize on ture (G. fulvus) chick ejected 34 g of junk including sheep different parts of carcasses (Kruuk 1967, Hertel 1994) with wool (Fig. 1), and junk is common in and below nest condors [Andean Condor (Vultur gryphus) and California ledges (M. Ghasabian pers. comm.). Junk is routinely Condor (Gymnogyps californianus)] and griffon vultures (all found at nests of G. bengalensis in Pakistan (M. Gilbert pers. eight species of Gyps) taking muscle and viscera from large comm.) In southern Africa, Benson et al. (2004) docu- mammals: our speculation here is mainly concerned with ment the extensive range of junk eaten by Cape Griffon these species, not other vulture species. Among the many (G. coprotheres), and review other studies from this region. similarities between these two groups is the unusual behav- As far as we know, comparable behavior has not been de- ior of swallowing indigestible, nonfood and often human- scribed on this scale for any other birds of prey or owls, made objects. For brevity we call this ‘‘junk.’’ Junk in- despite much intensive pellet analysis which would be ex- cludes fragments of glass, china, and plastic, metal objects pected to reveal such activity (e.g., Yom-Tov and Wool such as bottle tops, small rocks, sticks, grass, wool, and fur, 1997, Akaki and Duke 1998, Redpath et al. 2001). In this among other things. The scale of this behavior has only paper we speculate on the evolutionary function of this become apparent in recent years with the intensive surveil- unusual behavior, and the implications for conservation. lance necessary in conservation projects. In North America We suggest three possible functions for ingesting junk, the critically endangered California Condor has hatched which are not mutually exclusive. Firstly, as is often as- 17 chicks in the wild since the first breeding efforts of sumed, junk may be swallowed in the mistaken belief that reintroduced populations in California and northern Ari- it is a bone fragment. Condors and the larger vultures are zona (2001–2006). Of 10 nestlings hatched in the wild in unusual among birds of prey in that they feed mainly on California (2001–2005), only one survived to fledging the soft tissues (i.e., muscle and viscera) of large ungulate (Mee et al. 2007a). Seven of eight wild-hatched chicks in carcasses. Unlike some other birds of prey, which feed on California examined between 2002–2005 were found to small mammals or birds, they cannot consume their prey have consumed junk, and all nest sites contained this ma- whole. Bones are the primary source of calcium in the diet terial; six chicks had large quantities (30–204.5 g) of junk of birds of prey, but the large mammal carcasses on which in their guts, and three of these died in the nest area (Mee large vultures and condors feed have few bones small et al. 2007b). A fourth was later euthanized and two others enough for them to swallow, other than carpals, tarsals, were released back to the wild after 1.5–2.5 yr recovering at and phalanges. Their diet, if confined to soft tissues, may Los Angeles Zoo (U.S. Fish and Wildlife Service unpubl. therefore be deficient in calcium (Houston 1978). Adult data). This is also a common phenomenon in some Old birds probably can maintain calcium balance on such a di- World griffon vulture colonies. In Israel, there has been et, but, during the breeding season, females need to form heavy nestling mortality among Eurasian Griffons (Gyps eggshells and the chicks need higher calcium levels to mineralize their growing bones. The larger vultures have 1 Email address: [email protected] an unusually slow nestling growth rate, compared to other 236 SHORT COMMUNICATIONS VOL. 41, NO.3 cause of their long necks, condors and griffon vultures may find pellet ejection more difficult than do species with short esophagi. Those vulture species which consume large quantities of skin, such as the Old World Cinereous Vul- ture (Aegypius monachus) and Lappet-faced Vultures (Torgos tracheliotus) or the smaller New World Turkey Vulture (Cathartes aura) and Black Vulture (Coragyps atratus) are able to form large pellets regularly from the substantial quantities of hair they consume, in which smaller undigest- ed objects are embedded (Rea 1973, In˜igo Elias 1987). But vulture species such as condors and griffon vultures, which do not consume such large quantities of skin, may not always have sufficient material to form into functioning pellets, and in our experience do not produce pellets reg- ularly. When these vultures have small, undigested items lodged in their stomach they may deliberately seek other Figure 1. Junk (34 g) regurgitated by a Gyps fulvus nest- indigestible objects to swallow to enable them to accumu- ling in Armenia. Photo by Mike McGrady. late a sufficient volume of material for peristaltic action to eject it all as a pellet. This probably requires both material birds of their size, a growth strategy that may have evolved of sufficient mass and bulk against which the muscular as an adaptation to their low-calcium diet because it re- contractions of the esophagus can act, and sometimes also duces the daily calcium requirements of the chick (Hous- fibrous material to bind such junk together into a single ton 1978). Because of this low-calcium diet, vultures may functional pellet. Both vultures and condors apparently seek out small bones lying on the ground as alternative eat indigestible fibrous material such as grass, leaves, twigs, calcium sources, as is well known for many other bird spe- bark of shrubs, and hair, and such material can be found cies (see references in Ramsay and Houston 1999). Bone incorporated into their pellets together with solid objects can be digested readily in the acidic conditions of the (Koford 1953, Benson et al. 2004). The consumption of stomach (Houston and Copsey 1994). This need to find small, indigestible objects may therefore have been a be- calcium sources might account for condors’ and vultures’ havior that originally had clear adaptive value for condors consumption of pieces of white china, white PVC piping, and griffon vultures, and any naturally occurring junk plastic, glass, and similar white- or brown-colored junk in items swallowed would not normally have been life-threat- the mistaken belief that it is bone. However, it is perhaps ening, but would have assisted in pellet production. How- unlikely that this explanation alone can account for the ever, the situation has changed because humans have now consumption of metal bottle-tops, washers, electrical items, littered the environment with items that have sharp edges brightly colored or clear glass, ammunition casings, rub- which can lodge in, or even penetrate, the gut, and items ber, grass, sticks, and the other bizarre objects vultures which are toxic. These items probably are given to nest- regularly swallow (Collins et al. 2000, Ferro 2000, Benson lings unintentionally. When adults disgorge food from et al. 2004, Mee et al. 2007b), which could not be mistaken their crops into the mouths of the chicks, this transfer is for bone. indiscriminate; the bone fragments taken from the crops A second explanation may also be a consequence of of Cape Griffon chicks are not statistically different in size feeding on the soft tissues of large ungulate carcasses. It from those taken from the crops of adult birds (Benson et concerns the need to form pellets. No vertebrate gut con- al. 2004). But chicks might have weaker muscles in their tains an enzyme to digest keratin, so any keratin structure esophagus walls than do adults, and may not be able to that a bird swallows, including hair, horn, and hoof, will expel pellets as readily. This might explain the accumula- remain undigested once it reaches the stomach. All vul- tion of junk in the stomach of some chicks. In addition, tures will inadvertently eat some such keratin items, and because these species usually nest on rock ledges, chicks some species will consume more than others, depending have little opportunity to seek out fibrous indigestible ma- on the part of the carcass for which they are specialized. terial to help in the deliberate formation of a structured These will impede digestion if they are not ejected from pellet that can be expelled. This may be especially true for the stomach, and this is done through the production of nestling condors, usually confined to inaccessible cave pellets. In the stomach, pellets are formed from all mate- nests.