New World Vultures and Mammal Scavengers

This section looks at the relationship between New World vultures and mammal species that indulge in scavenging, namely feral dogs, jaguars, cougars, smaller wild cats, black and brown bears, and small mammals such as the raccoon.

The commonest mammalian scavengers in North America are coyotes (Canis latrans Say 1823), raccoons (Procyon lotor Linnaeus 1758) and opposums (Didelphis virginiana Gray 1821) (Wilmers et al. 2003; DeVault et al. 2011). These are commonly termed mesopredators, or mediumsized predators. In a study by Koford (1953) on the interactions between condors and coyotes, coyotes were dominant over condors; when a coyote approached in three incidents, 3, 10 and 20 condors flew away. Occasionally, coyotes would also eat sick or young condors.

In another study, where vultures were absent or did not detect small carcasses in an intensively farmed region in Indiana, USA, DeVault et al. (2011) found that raccoons and Virginia opossums removed 93% of mouse carcasses. Possibly, this dominance by abundant mesopredators had negative consequences for other scavengers. In highly modified contexts, effective mesopredators are likely to exist (Huston 1997; Wardle 1999). Such mesopredators indulging in scavenging in highly modified contexts are also recorded in other studies (see Litvaitis and Villafuerte 1996; Oehler and Litvaitis 1996; Crooks and Soule 1999; Gibbs and Stanton 2001; DeVault and Rhodes 2002; Sikes and Raithel 2002; DeVault et al. 2003, 2004; Prange and Gehrt 2004; Prugh et al. 2009; Ritchie and Johnson 2009).

An important factor for the large number of coyotes appears to be the decline and local extinction of wolves Canis lupus Linnaeus 1758 through much of North America (Berger and Gese 2007). Before and immediately after the European colonization of North America, wolves roamed over most of the continent, but with time they were exterminated by human action. Wolves were replaced by the more adaptive coyotes. Berger and Gese (2007) examined data on cause-specific mortality and survival rates of coyotes in wolf-free and wolf-abundant locations, and wolf and coyote presence in Grand Teton National Park (GTNP), Wyoming, USA, and the Greater Yellowstone Ecosystem (GYE) (located in Wyoming, Montana, and Idaho, USA). This study found that coyotes were numerically dominant over wolves, but their population densities varied with wolf abundance. Coyote population densities were actually 33% lower in areas with greater wolf abundance in GTNP. Coyote densities also declined 39% in Yellowstone National Park after the reintroduction of wolves. Wolves caused 56% of transient coyote deaths.

Another study, from southeast Canada, found that the selective killing of wolves resulted in wolf hybridization with the coyotes that consequently colonized the region (Rutledge et al. 2012). This concerned the Eastern Wolf (Canis lycaon) in Algonquin Provincial Park (APP), Ontario, Canada, where research culls killed the majority of wolves in 1964 and 1965 (about 36% of the park's wolf population) 'at a time when coyotes were colonizing the region' (Rutledge et al. 2012: 19). DNA studies found that this resulted in a decrease in an eastern wolf mitochondrial DNA (mtDNA) haplotype (C1) in the resident wolves and an increase in coyote mitochondrial and nuclear DNA. Later legislation that protected wolves outside the boundaries of the park in 2001 appears to have reduced the incidence of coyote DNA.

The study by Wilmers et al. (2003) took place in winter, when vultures were absent or rare in the Greater Yellowstone Ecosystem. Carcasses supplied by wolves and human hunters were attended by coyotes which were the dominant scavengers. The 'primary winter scavengers in Greater Yellowstone are, in order of dominance at carcasses, coyote, golden eagle, bald eagle, raven and magpie' (ibid. 997). The study found that the more dispersed carrion, mostly wolf kills were more often scavenged by coyotes.

The American Ornithologists' Union (1998) lists only the Turkey vulture as present in the Greater Yellowstone Ecosystem, but being a migratory bird it is probably absent most of the winter. The absence of Turkey and Black vultures from the study allows speculation on their position in such scenarios, but in an area where both are present, given the sense of smell of the Turkey Vulture and the social behavior of the Black vulture, it might be assumed they would arrive at carcasses (whether dispersed or localised) before most of the facultative scavengers.