Species considered raptors are subjects of monitoring programs, textbooks, scientific societies, legislation, and multinational agreements. Yet no standard definition for the synonymous terms “raptor” or “bird of prey” exists. Groups, including owls, vultures, corvids, and shrikes are variably considered raptors based on morphological, ecological, and taxonomic criteria, depending on the authors. We review various criteria previously used to define raptors and we present an updated definition that incorporates current understanding of bird phylogeny. For example, hunting live vertebrates has been largely accepted as an ecological trait of raptorial birds, yet not all species considered raptors are raptorial (e.g., Palm-nut Vulture [Gypohierax angolensis]), and not all raptorial birds are considered raptors (e.g., skuas [Stercorariidae]). Acute vision, a hooked bill, and sharp talons are the most commonly used morphological characters for delineating raptors; however, using those characters as criteria may cause confusion because they can be vague and exceptions are sometimes made. Old World vultures, for example, are in the family Accipitridae along with hawks and eagles, and thus are usually considered raptors despite their lack of sharp talons. We define raptors as species within orders that evolved from raptorial landbirds (Telluraves) in which most species maintained raptorial lifestyles. Raptors are therefore all species within Accipitriformes, Cathartiformes, Falconiformes, and Strigiformes. Importantly, we believe that seriemas (Cariamiformes) should also be considered raptors. Our definition combines phylogeny with morphology and ecology, and avoids ambiguity associated with owls, vultures, and shrikes. Establishing a common definition of raptors should improve interpretability across studies and lessen ambiguity of research and management recommendations.
Precise terminology is essential in science and conservation for comparison of findings across studies, communication within and across disciplines, concise drafting of policy instruments, and proper application of management actions. Birds typically classified as raptors, or birds of prey, have received much public and scientific attention over past decades, especially due to critical conservation issues surrounding them (e.g., Ratcliffe 1967, Prakash et al. 2003, Ogada et al. 2016). For these species, there exists discipline-specific infrastructure for research, monitoring, and conservation. Indeed, several textbooks and manuals directly address techniques to study and manage birds considered raptors (e.g., Giron Pendleton et al. 1987, Hardey et al. 2006, Bird and Bildstein 2007, Anderson et al. 2017) and large-scale monitoring programs track populations of birds designated as raptors across entire continents (e.g., Farmer and Hussell 2008, Kovács et al. 2008, African Raptor Databank 2017). In addition, several professional societies (e.g., Asian Raptor Research and Conservation Network, Neotropical Raptor Network, Raptor Research Foundation) and scientific journals (e.g., Journal of Raptor Research, Vulture News) are dedicated specifically to enhancing collaboration between researchers studying birds considered to be raptors and disseminating results of their studies.
Despite attention applied to species classified as raptors, and efforts to define raptor-specific terminology (Postupalsky 1974, Franke et al. 2017, Steenhof et al. 2017), there are no established or reliable criteria by which to include or exclude any individual taxon from the group “raptors.” Farquhar (2017) recently reviewed how the term “raptor” became synonymous with “bird of prey.” However, ambiguity remains regarding exactly which species we should consider raptors. Cooper (2002), for example, followed what he referred to as the “traditional method” of differentiation of raptors by including birds that were at the time within two Orders, specifically Strigiformes and Falconiformes. This latter order has more recently been subdivided by most taxonomic authorities to also include the Orders Accipitriformes and Cathartiformes based on phylogenetic evidence (Hackett et al. 2008). Many—probably most—publications covering raptors follow this convention (e.g., Bierregaard 1998, Virani and Watson 1998, Bird and Bildstein 2007, Donázar et al. 2016). Tradition thus holds that raptors include hawks, eagles, and allies, as well as Old World vultures (now in Accipitriformes), New World vultures (now in Cathartiformes), falcons, and caracaras (Falconiformes), and owls (Strigiformes). Despite tradition, however, varying groups of birds have been listed as raptors (e.g., Newton 1979, Andersen et al. 1985, C