BREEDING BIOLOGY OF THE ZONE-TAILED HAWK AT THE LIMIT OF ITS DISTRIBUTION

Twelve zone-tailed hawk (Buteo albonotatus) nest stands in eight terri tories were studied in northcentral New Mexico during 1990-92 to deter mine the nesting chronology, nesting habitat, diet, and productivity o f a population that is at the limit of the species' distribution. Zone -tailed hawks arrived on the study area from late March to early April and their breeding season ended in mid- to late September when the fa mily unit left the nest stand. All nest stands were in ponderosa pine (Pinus ponderosa) forests located in the bottom or on the slopes of st eep-walled canyons, and frequently in close proximity to cliffs. Stand basal area averaged 23.8 m(2)/ha and percent canopy closure averaged 69.2% (N = 10). Nest trees (N = 8) were large, averaging 23.8 m in hei ght and 59.8 cm diameter at breast height (dbh). The diet consisted of a mixture of mammalian, avian and reptilian prey species that are com mon in the study area. During 1990 and 1991 only one of six known terr itories successfully fledged two and one young, respectively. During 1 992 two new territories were located and these were the only successfu l nests (fledged one and two young). Although sample sizes are small, the productivity that we recorded is the lowest reported productivity of any zone-tailed hawk population. Reasons for the low productivity a re unknown.