Ecomorphological indicators of feeding behavior in Recent and fossil raptors

Modern aptors feed predominantly on animals and exhibit a wide range of feeding behaviors and prey preferences. The following six ecomorphs, based on feeding preferences served to classify members from all families of diurnal birds of prey: (1) avivores, which feed primarily on arian prey; (2) mammalivores, which feed primarily on mammalian prey; (3) herpetivores, which feed primarily on reptiles and amphibians; (4) piscivores, which feed primarily on fishes; (5) scavengers, which are primarily carrion feeders; and (6) generalists, which are opportunistic feeders on all of the above prey and on invertebrates. A series of skull-based indices were created to reflect functional aspects of prey preferences-calculated from measures of the cranium, maxilla (beak) and mandible--and were analyzed separately and with all units combined. The same indices were determined for 13 raptor species, including some extinct genera unearthed from the Pleistocene Rancho La Brea tar pits in California. A discriminant function analysis was used to assess the functional predictability of the indices for the extant raptors and also to predict the ecomorphs of the fossils. Results indicate that all of the indices combined provide the best predictor of prey preferences, especially for scavengers and avivores. Cranial and mandibular indices provide a better resolution than maxillary indices when considering only isolated elements. Eleven fossil species were assigned to their dietary categories with high probabilities and two were less definitely classified. Received 28 February 1994, accepted 16 May 1994. ECOMORPHOLOGY DESCRIBES the interrelationship between the functional morphology of organisms and their environment. It can be viewed as the environment shaping the design of the organism or the functional morphology of the organism determining its interaction with the environment (Wainwright 1991). Several workers have examined the correlation between aspects of morphology (e.g. wing, beak, and tarsus lengths) and ecological factors (e.g. habitat). These studies have included tropical frugivorous birds (Karr and James 1975), temperate scrub birds (Ricklefs and Travis 1980), grassland insectivores (Leisler and Winkler 1985), passerine communities (Miles et al. 1987), and North American kinglets (Keast and Saunders 1991). Other workers have used multivariate morphometrics to interpret the paleoecology of extinct penguins (Livezey 1989), boobies (Warheit 1992), anatids (Livezey 1993a), and raphids (Livezey 1993b). Raptors (defined here as diurnal birds of prey, including vultures) exhibit a variety of prey preferences. For this analysis, species were assigned to one of six ecomorphological categories (ecomorphs) based on their primary diet: (1) avivores, which feed predominantly on avian prey; (2) mammalivores, which feed primarily on mammalian prey; (3) herpetivores, which feed primarily on reptiles and amphibians; (4) piscivores, which feed primarily on fishes; (5) scavengers, which are primarily carrion feeders; and (6) generalists, which are more generalized feeders on all of the above prey, including invertebrates. The dietary categories are distributed among five families (Grossman and Hamlet 1964, Brown and Amadon 1968, Kemp and Crowe 1990, Sibley and Ahlquist 1990, Hoyo et al. 1994). Avivores, represented by falcons (Falconidae) and accipiters (Accipitridae), typically pursue and feed on avian prey. Mammalivores, which include most hawks and eagles (Accipitridae), prey on mammals from rodents to small ungulates. Herpetivores include the Secretarybird (Sagittarius erpentarius; Sagittariidae), the Laughing Falcon (Herpetotheres cachinnans; Falconidae), and harrier eagles (Accipitridae). Piscivores consist of the Osprey (Pandion haliaetus; Pandionidae) and certain genera of fish eagles (Haliaeetus and Ichthyophaga; Accipitridae). Scavengers were considered those species that primarily feed on carrion, given that most animals will scavenge opportunistically or under conditions of low food