Vultures, Facultative Scavengers and Predators

Introduction. This chapter looks at the relationships between New and Old World vultures and other birds and mammals. These relations concern predation, competition, cooperation, and adaptation. Carrion removal is a broad activity and a vital service for ecosystems (Sekercioglu 2006). Most animal carcasses are consumed by other vertebrates (Brewer 1994; DeVault et al. 2011). These vertebrate scavengers include not only obligate scavengers such as vultures, but predators such as raptors and carnivorous mammals (termed facultative rather than obligate scavengers). Disturbed or highly altered habitats may have less efficient ecosystem services (including scavenging) than intact, diverse habitats (Perfecto et al. 2004; Sekercioglu 2010). This is because the former may require behavioral adaptation from the scavengers and some species may not adapt to ecosystem instability (Campbell 2009). The competitive relationship between vultures and non- obligate scavengers is based on a shared attraction to carrion and may intrude into other relationships across the ecosystem.

Carrion presence influences the presence of obligate scavengers, facultative scavengers, predators and decomposers such as microbes and insects, at different tropic levels of the ecosystem (Janzen 1976, 1977; Rose and Polis 1998; DeVault et al. 2003, 2004, 2011; Wilmers et al. 2003a,b; Adams et al. 2010). Some avian predators situate foraging or breeding habitats partly based, at least in part, on carrion availability (Watson et al. 1992; Marr et al. 1995). Cortes-Avizanda et al. (2009a) found that the abundance of facultative scavengers such as common ravens (Corvus corax), red foxes, and jays (Garrulus glandarius) increased in the vicinity of ungulate carcasses, while the abundance of common prey species decreased, possibly as a result of prey avoidance or increased predation by the facultative scavengers. Predation by facultative scavengers on ground-nesting birds may also increase near carcasses (Cortes-Avizanda et al. 2009b). Competition between obligate scavengers, and non-obligate scavengers occurs both in undisturbed and disturbed environments. In such cases the adaptability of either group increases in importance (Campbell 2009).

This chapter compares the prehistoric, historic and current scenarios for vultures in all the continents. Other species are avian scavengers (raptors, storks, corvids, Larus gulls) and mammals (hyaenas, Canids, Felids and rodents). The hypothesis that vultures are relics from a past era of larger mammals is also examined, as is the argument that they may be supplanted in modern times by smaller more adaptable scavengers, such as feral dogs and cats, small mammal predators, corvids and gulls, suited to a cleaner, cultural world with little carrion. The extinction of the past megafauna, the recent mammal extinctions (e.g. that of the bison in North America), competition from other more adaptable avian species under human induced landscape and food-source change, and the ability of vultures to adapt to these changes at the Species, Genus and Family level are important issues.

The current trend is towards more disturbed environments, in which scavengers adapted to past environments may have adjustment problems. Much research has been conducted in undisturbed habitats (Selva et al. 2005; Selva and Fortuna 2007; Wilmers et al. 2011). However, also important for vultures are highly disturbed, human-dominated habitats (Campbell 2009). These include farmed lands and urbanized areas (Benton et al. 2003; Swihart et al. 2003; Prange and Gehrt 2004). In other words, can the majestic vultures that once fed on mastodons prepared by sabretoothed tigers now feed on rats, road kills and garbage?