Ecology and breeding behavior of the white-tailed hawk on the northern coastal prairies of Texas

Typescript (photocopy).I examined the ecology and breeding biology of a population of white-tailed hawks (Buteo albicaudatus hypospodius; 6 pairs, 1983, 1984; 7 pairs 1985) at the Attwater Prairie Chicken National Wildlife Refuge in Colorado County, Texas. The hawks nested almost exclusively (18/20 nests) in Macartney rose (Rosa bracteata). Incubation periods ranged from 29-32 days (x = 31.2 da.; Mar-Apr) and fledging occurred at 7-7.5 weeks (May-Jun). The fledglings were dependent upon their parents for up to 7 months after leaving the nest. Adults typically chased the immatures away at the onset of the breeding season. Subadult hawks occasionally returned to their natal territories. Utilization distributions (70%), were estimated using sight locations from 10 pairs of adults (1984-1985) and radio locations from 2 of the immatures (1984). Immatures dramatically increased their home ranges over their first 7 months of flight (37 ha-147 ha, x = 59 ha for bird #9; 16 ha-199 ha, x = 72 ha for bird #14). Home ranges of adult males were nearly 3 times larger than those of females during the breeding season (males, x = 33 ha, females, x = 14 ha, 1984; males, x = 34 ha, females, x = 13 ha, 1985). Males increased and females decreased their home ranges after the onset of incubation. All pairs always copulated and always laid eggs. Nesting success was high in 1983 (100%) and 1985 (100%) and lower in 1984 (71%). Breeding adults performed an interesting behavior which may function in courtship or pair bonding, not previously described, involving placing of long woody stems or branches up to 2.5 m in length on nests. I recorded 1 instance of renesting when 1 egg was abandoned early in the season; the pair fledged 2 young later in the season. Time-activity data suggest this species alters the length of its daily incubation sessions, possibly in accordance with temperature. From field observations, I noted distinct intersexual variation in alarm calls which is useful in field-sexing. Prey taxa are variable: biomass is composed chiefly of small mammals, birds, and reptiles