In 1963, 158 (48%) of 326 Bald Eagle (Haliaeetus leucocephalus) nests surveyed on Kodiak National Wildlife Refuge (KNWR) were occupied. Nesting success was 66%. Production rates of young per occupied nest and young per successful nest were 1.10 and 1.66, respectively. In 2002, 538 (55%) of 979 Bald Eagle nests were occupied. Nesting success was 52% and production of young per occupied nest was 0.87; however, production of young per successful nest remained at 1.66. Since 1963, the number of Bald Eagle nests on KNWR increased 241% and the total production of young increased 425%. The factors that have influenced this increase are not known. Despite decreased nest success and lower productivity per occupied nest, the KNWR nesting Bald Eagle population continues to increase.

We studied home-range characteristics of adult Mexican Spotted Owls (Strix occidentalis lucida) in southern Utah. Twenty-eight adult owls were radio-tracked using a ground-based telemetry system during 1991–95. Five males and eight females molted tail feathers and dropped transmitters within 4 wk. We estimated cumulative home ranges for 15 Spotted Owls (12 males, 3 females). The mean estimate of cumulative home-range size was not statistically different between the minimum convex polygon and adaptive kernel (AK) 95% isopleth. Both estimators yielded relatively high SD, and male and female range sizes varied widely. For 12 owls tracked during both the breeding and nonbreeding seasons, the mean size of the AK 95% nonbreeding home range was 49% larger than the breeding home-range size. The median AK 75% home-range isopleth (272 ha) we observed was similar in size to Protected Activity Centers (PACs) recommended by a recovery team. Our results lend support to the PAC concept and we support continued use of PACs to conserve Spotted Owl habitat in Utah.

We investigated the relationship between late summer abundance of small rodents and fall migrant abundance of two nocturnal avian predators, the Boreal Owl (Aegolius funereus) and the Northern Saw-whet Owl (A. acadicus), during their fall movement/migration. In the eastern Canadian boreal forest, Boreal Owls are considered resident (with irruptive movements to the south thought to occur during periods of low prey availability), and Northern Saw-whet Owls migratory. Data on late summer abundance of small rodents collected between 1995 and 2004 were used to develop an index of prey availability. Data on the number and age of irrupting/migrating owls were collected between 1996–2004 (mid-September to late October) using audiolures and mist nets. Our study revealed strong evidence of (1) a negative relationship between the abundance of small rodents and movement of Boreal Owls and (2) a positive relationship between the abundance of small rodents and the number of migrating juveniles and second year Northern Saw-whet Owls. In the latter case, it suggests that prey availability can strongly influence breeding success of this species, which is at the northern limit of its breeding range.

We measured breeding success of Spotted Owlets (Athene brama) in two habitats, villages (human habitations) and rural areas (open country) in India. We quantified habitat types in 500-m-radius circles surrounding 53 nest sites and examined owlet pellets collected at nest sites in both areas, to describe owlet diet. Breeding success was higher in the human habitations than in open country (3.3 young per successful nest vs. 2.2, respectively, P < 0.001). Diet at nests in human habitations contained more rodents and other noninsectivorous non-arachnid prey (by biomass and species richness) than those in open country (P < 0.01 for rodents and P < 0.001 for other prey). We used multivariate linear regression to examine which factors of habitat and diet most influenced breeding success and found that only the percentage of rodents, and the percentage of other prey were included as statistically significant variables in our final model. Thus, the most significant determinant of breeding success of Spotted Owlets was high-value prey items, which were more abundant in the areas of human habitations.

Populations of three Gyps vulture species in the Indian subcontinent have undergone recent rapid declines due to elevated mortality rates caused by diclofenac poisoning. Researchers have proposed that vultures adopt a previously-undescribed neck-drooping posture prior to death. Our study investigated two hypotheses: (1) neck drooping is temperature-dependent, (2) neck-drooping is indicative of poor health in Oriental White-backed Vultures (Gyps bengalensis) and is a prelude to death. Observations of neck-drooping were highly seasonal, with the majority of vultures observed neck-drooping in the hot season from April to October and no vultures observed neck-drooping during the cold months of December and January. Above a calculated threshold ambient temperature of 15.4°C (95% CI 9.9–22.5°C), there was a significant positive correlation between temperature and the proportion (expressed as an angular transformation) of vultures observed neck-drooping. Neck-drooping vultures were observed significantly more frequently with their back toward the sun with their head in their own shade than birds that were not neck-drooping, and vultures that were not neck-drooping were observed more frequently facing the sun than those neck-drooping. Together, these observations strongly suggest that neck-drooping posture has a role in thermoregulation. In contrast to the highly seasonal pattern of neck-drooping, mortality of vultures occurred in all months of the year. This finding indicates that neck-drooping has low specificity and sensitivity as an indicator of poor health and impending death in vultures.