The Ashy-faced Owl (Tyto glaucops) is endemic to Hispaniola, where the Barn Owl (T. alba) became established after ca. 1950. I examined 8322 vertebrate prey of the two species, using regurgitated pellets and prey remains from 12 localities in five habitats in the Dominican Republic to determine diets and feeding-niche characteristics of the owls. Owl diets differed among prey classes in frequency and biomass. Mammals, mainly introduced rodents, predominated in the diets of Ashy-faced Owls (52.0% frequency, 73.9% biomass) and Barn Owls (76.7% frequency, 90.7% biomass), with bats forming a substantial proportion for both species (Ashy-faced Owl: 11.1% frequency, 2.6% mass; Barn Owl: 12.2% frequency, 2.2% mass). Birds made up a greater proportion of Ashy-faced Owl prey (28.8% frequency, 14.8% mass) than of Barn Owl prey (12.3% frequency, 5.1% mass). Reptiles and amphibians were unequally represented in Ashy-faced (19.2% frequency, 11.3% mass) and Barn (11.1% frequency, 4.3% mass) owl diets. Niche overlap was moderate overall (α  =  0.60). Ashy-faced Owl prey materials contained 125 vertebrate species, whereas Barn Owl materials included 114 species, with 92 species in common between the two owls. The Ashy-faced Owl had a more diverse prey base (H′  =  3.04, D  =  6.32, J  =  0.610) than did the Barn Owl (H′  =  2.21, D  =  2.93, J  =  0.444). I could not determine whether niche overlap resulted in competition between the two owl species.

Long-term monitoring is important for ensuring effective conservation of raptor populations. Raptors also can serve as indicators of biodiversity and ecosystem condition. Therefore, effective monitoring of raptor populations yields the added benefit of helping to evaluate the status of ecosystems. Spring counts of migrating raptors at concentration points may contribute to these goals, particularly by providing insight into the vital demographic rates underlying population trends. Although much is known about the monitoring value of autumn migration counts in North America, little research has addressed the value of spring counts. We compared counts at seven spring watchsites to those at seven autumn watchsites matched by region (Southwest, Great Lakes, and Northeast) to assess the value of spring counts for population monitoring. Our analyses suggested that population indexes derived from spring migration counts provided estimates of population change that differed overall from autumn migration counts in the same region. The concordance of spring and autumn trends was higher in the Southwest and Northeast than in the Great Lakes region, suggesting greater variation in the seasonal representation of populations in the latter region. The average precision of spring trend estimates was better than for autumn estimates in the same region in two of three regions, and the estimated rates of change often were lower in spring. Spring counts enhanced the ability to estimate population trends for species that are less common in autumn counts, including the Rough-legged Hawk (Buteo lagopus) and Red-shouldered Hawk (B. lineatus). To realize fully the value of spring counts, we recommend the establishment of additional spring watchsites in areas that concentrate migrants in autumn, but do so to a lesser extent in spring, as well as additional research to define the populations sampled by autumn and spring counts.

The associations among corticosterone levels, energy stores, and stress are highly relevant to bird migration physiology. Many birds maintain elevated baseline corticosterone levels during migration, yet they frequently modulate additional glucocorticoid secretion, probably to protect their flight muscles from catabolism. We report on the adrenocortical response to capture and handling stress in three Accipiter species, the Sharp-shinned Hawk (Accipiter striatus), the Cooper's Hawk (A. cooperii), and the Northern Goshawk (A. gentilis) during fall migration. We found mean baseline corticosterone levels to be similar in Sharp-shinned Hawks and Northern Goshawks, but significantly higher in Cooper's Hawks. Likewise, mean baseline levels of corticosterone did not differ in hatch-year and after-hatch-year male and female Sharp-shinned Hawks and Northern Goshawks, but they were higher in adult male Cooper's Hawks than adult females. Mean corticosterone levels did not increase significantly after 30 min of capture and handling stress in any of the three species, indicating that they modulated their adrenocortical stress responses. Fat scores were not correlated with baseline corticosterone levels, except in Sharp-shinned Hawks, in which elevated baseline corticosterone levels were associated with low fat scores.

We examined changes in diet composition during the breeding period for the endangered Lesser Kestrel (Falco naumanni). Pellets were collected weekly from the last week of March until the first week of July in a colony located in southwestern Spain. Diet composition was evaluated in terms of frequency of occurrence of different prey, mean prey weight, and prey richness of each pellet. Generalized additive models were used to analyze the predictive ability of calendar week (as an index to prey availability), reproductive week (as an index to breeding demands), and nest identity (as a proxy for individual preferences/abilities) on the above dietary metrics. Primary prey species were the mole cricket (Gryllotalpa gryllotalpa) during courtship, the saddle-backed bush cricket (Ephippiger ephippiger) during incubation, and the migratory locust (Locusta migratoria) and the white-faced bush-cricket (Decticus albifrons) during the nestling phase. Small mammals were only important during some particular weeks at the beginning of the nestling period. Mean prey weight increased as the breeding season advanced, while species richness tended to decline. This was mainly due to the decreasing contribution of small prey items such as beetles to the diet and the greater incidence of large prey species. Calendar week and reproductive week had similar abilities to predict diet composition, and were better predictors than nest identity. Models fitted to particular prey species had greater explanatory power than models fitted to prey groups. Likewise, models fitted to those prey species that we considered “preferred” fitted better than those considered “refuge” prey.

Raptors were monitored monthly over a three-year period in a protected area in central Kenya. The number of raptors declined more than 40% per year. Scavenging birds accounted for most of the decline; sightings decreased by 70% during our surveys, although these declines were not statistically significant. During the time of the study, the overall populations of large wild herbivores showed little change, whereas domestic herbivores, particularly sheep and goats, increased markedly, suggesting that food limitation was not the cause of the vulture declines at the study site. Possible causes of raptor decline include the consumption of poisoned baits, which are placed by pastoralists to kill large predators that attack livestock. Scavenging birds provide one of the most important yet underappreciated ecosystem services of any avian group. The rapid decline of scavenging birds, especially vultures, in central Kenya warrants additional population monitoring to understand whether declines are local or regional, and to elucidate causes of population decreases.

The Western Marsh Harrier (Circus aeruginosus) is a summer visitor in northern, eastern, and central Europe. Some birds, mostly juveniles and adult females, winter in the Mediterranean region, while others cross the Sahara to winter in tropical Africa. Unlike other Accipitridae, which use primarily soaring flight over land during migration, Western Marsh Harriers tend to move on a broad front, with long, powered flights over water. In the last two decades, several researchers have investigated the migration of this species through the Mediterranean basin using direct observations, radar, band recovery data, and satellite telemetry. We here present a short review of these investigations and results.