Between October 2000 and December 2006, we located 30 nests of 25 breeding pairs of Harpy Eagle (Harpia harpyja) in the province of Darien, Panama. Most nests were in primary tropical rain forest at a mean altitude of 132 m (range  =  50–305 m). Applying the Polygon and the Maximum Packed Nest Density (MPN) methods, we estimated nest densities of 4 and 6 nests/100 km², with each breeding pair occupying 24 and 16 km² of forest, respectively. This nesting density is the highest reported for the species throughout its breeding range. Although most nests (n  =  25) were in primary forest, the average distance from small parcels (<2 ha) of agricultural fields was 2.5 km. By extrapolating the nesting density results from the selected study area in Darien to the entire area of Panama with suitable forest cover at altitudes below 350 m, we estimated that the Harpy Eagle population size could range between 806 and 1208 pairs. Greater conservation effort should be placed on potentially suitable Harpy Eagle habitat. We also suggest that educational outreach measures should be an important part of conservation efforts throughout Panama.

The Rock Eagle-Owl (Bubo bengalensis) was recently recognized as a species, with a distribution restricted to the Indian subcontinent. We studied breeding biology, habitat use, diet, and nesting density of 44 pairs of Rock Eagle-Owls in western Maharashtra state (India) for two successive breeding seasons (2004–05 and 2005–06). We present here for the first time (a) egg shell thickness (0.305 ± 0.001 mm; range: 0.303–0.306 mm); (b) egg-laying interval (1.7 ± 0.5 d; range: 0.5–4 d); (c) incubation period (33–34 d); (d) hatching pattern (asynchronous); (e) breeding success (1.5 ± 0.9 fledglings per occupied nest; range: 0–4 fledglings); and (f) post-fledging dependency period (6 mo, from April to September). Most productive nesting territories have several alternative nest sites and open landscapes such as agricultural lands and scrublands, which offer high-value foods including rodents, birds, and chiropterans. Early onset of breeding was positively correlated with the presence of high-value foods in the diet.

Burrowing Owls (Athene cunicularia) routinely collect and scatter dry manure of mammals around their nesting burrows. Recent studies have suggested this behavior attracts insect prey to the nesting burrow. However, some Burrowing Owls do not use manure, but instead, collect and scatter other materials (e.g., grass, moss, paper, plastic) around their nesting burrow in a similar fashion. Use of these materials seemingly contradicts the prey-attraction hypothesis. Using observational and experimental methods, we tested whether Burrowing Owls preferred manure to other materials commonly found at nesting burrows in eastern Washington. We found a wide variety of materials at nests, but grass and manure were the most common materials. The amount of manure present at nests was negatively correlated with the amount of other materials, and with the distance to the nearest source of manure. Burrowing Owls showed no preference between horse manure and grass divots at experimental supply stations that we placed near nesting burrows. They did prefer these two materials to carpet pieces and aluminum foil (both materials that are often found at Burrowing Owl nests). Our results did not support the premise that Burrowing Owls specifically seek out manure when lining their nesting burrows. The unusual behavior of collecting and scattering mammal manure and other debris at Burrowing Owl nests may serve functions other than (or in addition to) prey attraction and alternative hypotheses need further testing before the function of this behavior is certain.

On the Falkland Islands (Malvinas), raptors historically were perceived as a threat to livestock, and consequently were widely persecuted through the mid-twentieth century. Conservation measures now minimize persecution and have facilitated increases in raptor populations, but the ecology of raptors on the Falkland Islands (Malvinas) remains poorly understood. We investigated social hierarchies within an assemblage of nonmigratory raptorial scavengers: Variable Hawk (Buteo polyosoma), Striated Caracara (Phalcoboenus australis), Southern Caracara (Caracara plancus), and Turkey Vulture (Cathartes aura jota). During thirty observation sessions of 30 min each, we recorded 1386 aggressive interactions involving one or more of these species. We found that Variable Hawks were aggressors in 98% (95% CI  =  96–100%) of interactions with Striated Caracaras, 82% (69–95%) of interactions with Turkey Vultures, and 80% (72–88%) of interactions with Southern Caracaras. Southern Caracaras were aggressors in 100% of interactions with Striated Caracaras, and 90% (80–100%) of interactions with Turkey Vultures. Turkey Vultures were aggressors in 71% (61–82%) of interactions with Striated Caracaras. Within species, we found adult Southern Caracaras were aggressors in 78% (72–84%) of interactions with conspecific juveniles and 76% (68–85%) of interactions with conspecfic subadults. Adult Striated Caracaras were aggessors in 100% of interactions with conspecific juveniles and 97% (91–100%) of interactions with conspecfic subadults. Predicted patterns of size-based dominance typical of complex African and South American avian scavenger assemblages were not observed in the relatively simple assemblage of the Falkland Islands (Malvinas), but we did observe single-species groups of up to 83 Southern Caracaras and 42 Striated Caracaras.

We used roadside survey data collected from 19 routes over three consecutive winters from 2007–08 to 2009–10 to compare habitat associations of male and female American Kestrels (Falco sparverius) in the Central Valley of California to determine if segregation by sex was evident across this region. As a species, American Kestrels showed positive associations with alfalfa and other forage crops like hay and winter wheat, as well as grassland, irrigated pasture, and rice. Habitat associations of females were similar, with female densities in all these habitats except rice significantly higher than average. Male American Kestrels showed a positive association only with grassland and were present at densities well below those of females in alfalfa, other forage crops, and grassland. Males were present in higher densities than females in most habitats with negative associations for the species, such as orchards, urbanized areas, and oak savannah. The ratio of females to males for each route was positively correlated with the overall density of American Kestrels on that route. Our findings that females seem to occupy higher quality habitats in winter are consistent with observations from elsewhere in North America.

We studied the diet of breeding Ospreys (Pandion haliaetus) in the Cape Verde archipelago during 2006, using prey remains recovered at 21 nests and perches on the islands of São Vicente, Santiago, Santa Luzia, Boavista, Branco, and Raso. We identified a total of 1264 individual fish prey items of 35 species. Diet was dominated (>80%) by only six fish species, including Trachinotus ovatus, Exocoetus volitans, Aulostomus strigosus, Sparisoma cretense, Sardinella maderensis, and Tylosurus acus. Dominant prey species varied among islands, but diet similarity was greater between nearby islands. Pelagic species were consumed most frequently (>60%) in Boavista and Santa Luzia, whereas demersal reef fish dominated (>50%) in the other islands. The fish consumed were generally large, though there was wide variation in estimated length (20.7–62.2 cm) and weight (49–1117 g). A comparison of Osprey diet with Cape Verde fisheries suggested that the potential for conflict is low, due to minimal overlap in the primary species caught. Changes in marine productivity associated with the ongoing moderate warming of the Canary Current System may represent a threat, though there is considerable uncertainty about the type and magnitude of these effects. Monitoring of Osprey numbers, breeding success, and diet is required to detect any changes associated with availability of food sources, and such monitoring may also provide a relatively simple and inexpensive method to track long-term changes in littoral fish assemblages.