Diversity in Body Size and Feeding Morphology within Past and Present Vulture Assemblages

Abstract

Abstract. Vultures comprise two geographically isolated and taxonomically distinct groups, Old World accipitrids and New World vulturids, and provide a classic case of convergent evolution. In both regions, several species of vultures often feed together in large numbers on carcasses. Behavioral studies of East African and Amazonian vultures have documented parallels in apparent ecological separation within this guild of specialized scavengers. Here morphological differences in skull, beak, and mandibular dimensions are compared among sympatric vultures in East Africa, South Africa, the Indian subcontinent, Amazonia, and the Pleistocene Rancho La Brea deposits in California. A discriminant function analysis based on morphological indices separates three basic feeding types: rippers, gulpers, and scrappers. Vultures of the three feeding types are present in both Pleistocene and Recent assemblages and show a similar distribution of body sizes into three size classes, suggesting that competition has favored similar pathways of ecological separation. This is true even when phylogenetic differences among some of the assemblages are partially accounted for. Comparisons between the fossil and extant New World vultures indicate that more specialized species were prone to extinction and that there has been a reduction in body size since the Pleistocene.

Dietary shifts in two vultures after the demise of supplementary feeding stations: consequences of the EU sanitary legislation

“…Within those guilds embracing species having carnivore food habits, the diversity of the diet may be also based mainly on the variability in size of the prey (Begon et al 2006). In the case of carrion-eater guilds, the degree of sharing of common resources (carcasses) depends on morphological and behavioral traits (Mundy et al 1992;Hertel 1994;Hertel and Lehman 1998). Thus, in each geographical region, there is one or two species of "true" scavengers ("Gyps" vultures and some Cathartidae in the Old and New World, respectively); their morphological adaptations and their social behavior allow these vultures to specialize in the consumption of large carcasses (Houston 1983;König 1983;Wallace and Temple 1987).…”

The shapes of bird beaks are highly controlled by nondietary factors

“…Despite some differences in the positions of Accipitridae and Falconidae between different topologies (25,26), raptor families are consistently recovered at the base of both major landbird clades, and a raptorial ancestor for the landbird radiation has been suggested (25). Extensive morphological and dietary convergence is seen between raptor families [for instance, between scavenging Old and New World vultures (27) and the avivore sparrowhawks (e.g., Accipiter nisus) and falcons (e.g., Falco columbarius)] alongside the repeated evolution of recognizable ecomorphotypes (e.g., eagles…”

Two Old World vultures from the middle Pleistocene of northeastern China and their implications for interspecific competition and biogeography of Aegypiinae

“…The relatively wider skulls of our new materials (Table 2, Fig. 4) provide greater moment arms or mechanical advantage for neck muscles that control skull movements and thus probably reflect a greater ability of the skull to twist and rip tough parts from a carcass (Hertel, 1994). The broader fossa temporalis and more distinct temporal scar in the two new fossils provide extensive insertion for M. adductor mandibulae externus rostralis (musculus temporalis) that produces the main strength for jaw closing.…”

“…There was a diverse assemblage of large herbivores that would have provided scavenging vultures with abundant large carcasses as a food resource. Old World vultures have three chief forms of feeding: pulling, tearing, and pecking (see above; Kruuk, 1967;König, 1983;Hertel, 1994). The large-sized A. monachus, Torgos, and Trigonoceps belong to the tearing type, characterized by a more compact, wider skull with a powerful beak adapted for opening carcasses and tearing off tough and coarse parts.…”

“…Gulpers (pulling; griffon vultures) have a long, bare neck, intermediate beak strength, narrow skull, and primarily feed on the soft viscera and meat. Necrosyrtes and Neophron, a genus of Gypaetinae, belong to the third group, the scrappers (pecking), which are smaller than the other vultures and have thin, slender bills adapted to peck smaller scraps on and around the carcass (Kruuk, 1967;Hertel, 1994 Fossil records of Old World vultures occur in both the Old and the New Worlds as early as the early Miocene and become more frequent in the Pleistocene (Feduccia, 1996; Table 1). Compared with the Old World, the New World has an unexpectedly diverse and rich fossil component of Aegypiinae, especially Neophrontops, which is represented by six species spanning the late Miocene to the late Pleistocene, and thus was a relatively successful group.…”