The Harris's Hawk (Parabuteo unicinctus), also known as the Bay-winged Hawk, and previously as “Harris' Hawk” (Ferguson-Lees and Christie 2001), is a conspicuous bird of desert and savannah environments. The species appears to have been a model for the Thunderbird or Sacred Bird of several Native American societies (Moore 1986b), and because Harris's Hawks bond easily to human handlers, the species continues to play important roles in human culture. Harris's Hawks are “preadapted” to work with hunting partners (other Harris's Hawks, humans, or dogs), and have the capacity to capture both large prey such as jackrabbits and small, maneuverable birds. Consequently, Harris's Hawks are popular among falconers and serve widely as envoys of the natural world in raptor free-flight education programs (Parry-Jones 2001, Harris 2002, Millsap and Allen 2006).
Though Native Americans apparently recognized the unique social ecology of Harris's Hawks long before European settlers arrived, the behavior and biology of the species was essentially unrecognized by science until the 1970s. At that time a revealing series of studies was published describing the unique social ecology of Harris's Hawks (Mader 1975a, 1975b, 1977a, Whaley 1979). Reports of cooperative hunting, group breeding, intra-group social hierarchies, and year-round nesting inspired fervent studies through the 1980s and 1990s (Bednarz 1987a, 1987b, 1988c, Dawson and Mannan 1989, 1991a, 1991b, 1994).
These efforts revealed that Harris's Hawks breed in social units that vary from an adult pair to as many as seven individuals, including both adults and subadults. Depending somewhat on geographic location, groups exhibit both monogamy and polyandry, and sometimes polygyny. Harris's Hawk groups employ some of the most sophisticated cooperative hunting strategies known in birds. For instance, group members will chase prey in open environments by leap-frogging past one another as prey evades successive attacks, will simultaneously converge on fleeing prey from multiple directions to cut off escape, and will surround the hiding place of hidden prey while one bird approaches on foot to flush their quarry so group mates may capture it. Such cooperative hunting is probably intimately related to the birds' social nature, but whether cooperative hunting is primarily a cause or an effect of group living remains unresolved.
As the life history of the Harris's Hawk became known, interest spread to comparisons between Harris's Hawks and other species, including Red-tailed Hawks (Buteo jamaicensis; Mader 1978), and Swainson's Hawks (Buteo Swainsoni; Gerstell and Bednarz 1999) in the U.S., and Galápagos Hawks (Buteo galapagoensis) in the Galápagos Islands of Ecuador (Faaborg and Bednarz 1990). Interest in intraspecific interactions between Harris's Hawks and other raptors expanded to Crested Caracaras (Caracara cheriway) in Mexico (Rodríguez-Estrella and Rivera-Rodríguez 1992), and Black-chested Eagles (Geranoaetus melanoleucus) and Red-backed Hawks (Buteo polyosoma) in Chile (Jiménez and Jaksić 1989, 1991, 1993; Orellana and Rojas 2005).
Across these studies, the unique social ecology of Harris's Hawks was found to be inexorably linked to many other aspects of the behavior and biology of the species. As research moved into a more management-oriented phase in the 2000s, the connection to sociality continued. Harris's Hawks are now colonizing urban areas in Arizona (Dwyer and Mannan 2007) and in Chile (Figueroa and Gonzalez-Acuna 2006, Jaksić et al. 2001), where the species faces unique risks arising from group living. Many or all group members often perch together on a single structure. In urban areas, where native perches have largely been replaced or superseded by anthropogenic structures, social perching often occurs on electric power poles. Unless power poles are carefully modified to minimize electrocution risks, when multiple hawks occupy a single pole the likelihood increases that at least one individual will occupy a position on the pole where electrocution is a hazard (Dwyer 2004, 2006, 2009).
Much of the early science of Harris's Hawks was accumulated at the extreme northern boundary of the species range. Recent studies, particularly in Chile (Jiménez, J. E. and F. M. Jaksić 1993, Orellana and Rojas 2005, Pavez et al. 2010), are providing international balance to our understanding of the species, but additional research throughout the species' range in Central and South America is needed to maximize conservation and management of the species.