Introduction

The Harris’s Hawk, also known as the Bay-winged Hawk, is perhaps the most enigmatic bird of prey in North America. Less than two decades ago, the behavior and ecology of this species were essentially unknown to science. Preliminary reports of group breeding and year-round nesting inspired several fervent studies on this species in the southwestern United States. These efforts spawned several intriguing discoveries, much data, and conflicting opinions about the evolutionary basis of the bizarre behavioral traits exhibited by this raptor. The Harris’s Hawk is now one of the best-studied, yet least-understood, raptors in North America.

The most conspicuous feature of the Harris’s Hawk biology is its social nature. This species nests in social units that vary from an adult pair to as many as seven individuals, including both adults and immatures. Depending somewhat on geographic location, groups exhibit both monogamy and polyandry, and sometimes polygyny. Harris’s Hawk groups employ one of the most sophisticated cooperative hunting strategies known in birds. Such cooperative hunting is probably intimately related to the birds’ social nature, but whether cooperative foraging is primarily a cause or an effect of group living remains unresolved.

Another unusual trait of this species is its ability to breed year-round in temperate-climate desert habitats in North America. Viable eggs or young occur every month of the year. Although most North American Harris’s Hawks nest in spring (Mar–Jun), some females will lay second and even third clutches after their first breeding attempt fails or succeeds. These “extra” nesting attempts seem to be highly dependent on prey availability and occur commonly in some areas and during some years; in most regions, however, they are rare, and they are nonexistent when food is scarce.

The Harris’s Hawk is a conspicuous bird of desert and savannah habitats with dispersed saguaros (Cereus giganteus) or small trees that provide hunting perches. The availability of dispersed perches is key to the cooperative hunting style of this species, which hunts primarily by making short flights (50–400 m) from perch to perch.

Because of its cooperative nature, maneuverability, and lightning-fast acceleration, the Harris’s Hawk has become a popular bird for falconry. These hawks bond easily to human handlers, are “preadapted” to work with hunting partners (other Harris’s Hawks, humans, or dogs), and have the capacity to capture both large prey (jackrabbits) and small, maneuverable birds.

Evidence suggests that the Harris’s Hawk may be the model for the Sacred Bird or Thunderbird of several Native American cultures (Moore 1986). Native Americans believed that the Thunderbird lived in extended families similar to those of the Harris’s Hawk.