African owls are relatively little known and studying them is difficult due to negative effects of cultural beliefs and consumptive uses of owls. Over a 5-yr period from 2004–08, we studied the breeding ecology of 13 pairs of Mackinder's Eagle-Owls (Bubo capensis mackinderi), a subspecies of the Cape Eagle-Owl (B. capensis), inhabiting a densely populated farming community in central Kenya. Mean owl density was 0.24 pairs/km² and mean nearest neighbor distance averaged over all years was 1.9 km. Most nests (65%) were located in a cave or on a covered ledge, and mean nest site elevation was 2191 m asl. Nests were located close to farms and grasslands, but far from forests. Initiation of breeding was associated with rainfall patterns. Mean breeding success was 51% and reproductive rate was 1.36 young fledged per successful pair. Increased reproductive success was associated with breeding after the long rainy season, nesting on cliffs or covered ledges, and nesting close to grasslands and human habitation. The majority (59%) of recorded owl deaths were caused by human activities and poisoning was the most common source of mortality. Compared to other populations of Bubo spp., the birds in our study area had a high breeding density but a low reproductive output. Human-induced mortality may be negatively affecting productivity in this population.

The population of Bald Eagles (Haliaeetus leucocephalus) breeding in Florida Bay, located within Everglades National Park, has been the subject of one of the longest running monitoring programs for any large raptor species worldwide, with reproductive data collected for 49 breeding seasons since 1958. The overall reproductive trends in this nesting population indicated that the population has transitioned from one at or near carrying capacity to one in decline, with territory occupancy decreasing as much as 43%. This contrasted with observed trends for the state of Florida, where populations increased >300% over the past 25 yr. The rate of nesting attempts in Florida Bay remained high (0.83 ± 0.11 [SD]; number of active territories/number of occupied territories) over the period. Mean annualized brood size was 1.48 ± 0.16 young/successful territory and mean productivity was 0.81 ± 0.21 young/occupied territory, which are comparable to those of other Bald Eagle populations. There were significant increases in ratios of active territories/occupied territories, successful territories/occupied territories, and young/occupied territory, despite decreased occupancy. Increases in these rates have allowed overall production of the Florida Bay population to remain stable; however, given the current decreasing trend in territory occupancy, this population should be considered at risk. Changes in Bald Eagle reproductive parameters corresponded with significant ecological changes documented in Florida Bay and southern coastal Everglades and may serve as possible long-term indicators for the health and recovery of the southern Everglades as restoration efforts progress.

Relationships between apex predators and mesopredators have been poorly documented in predatory birds. Prediction from intraguild predation (IGP) theory suggests that following the recovery of Peregrine Falcon (Falco peregrinus) populations, the potential for Merlins (F. columbarius) to experience mesopredator suppression should increase where these species share habitat and prey resources. In Washington, both falcons prey on Dunlins (Calidris alpina) in estuarine ecosystems during the nonbreeding season. To investigate whether mesopredator suppression may have occurred, I compared aspects of the hunting behavior of Merlins at an estuary in western Washington between 1999 and 2009, when Peregrine Falcons were regularly present, with hunting behavior in the 1980s, when Peregrine Falcons did not occur at the site. Merlin hunting behavior changed substantially between the two periods. Following Peregrine Falcon recovery, Merlins hunted less frequently, used hunting flights of shorter duration and that involved fewer capture attempts per successful flight, and captured prey closer to the cover of vegetation, results that are consistent with IGP theory. Prior to Peregrine Falcon recovery, Merlins appear to have assumed the role of apex falcon predator at the site; Merlins currently coexist with Peregrine Falcons, and have altered their hunting behavior which may reduce their risk of IGP.

Sexing of raptors is important for understanding their ecology and demography. Males and females of monomorphic species such as Red-shouldered Hawks (Buteo lineatus) may be distinguished using molecular and morphometric techniques. We collected blood samples and morphometric measurements from adult and nestling Red-shouldered Hawks in southern Ohio. We determined sex via amplification of the sex-linked chromo-helicase-DNA-binding gene and polymerase chain reaction. We used a suite of morphometric measurements to generate a recursive partitioning classification tree and in a linear discriminant analysis to determine the sex of adults and nestlings. For adults, the recursive partitioning tree utilized only mass to distinguish sexes, with an overall successful classification rate of 94%. For nestling hawks aged approximately 3 wk and older, mass and toepad (footpad) length were used to distinguish the sexes, with an overall successful classification rate of 91%. The ability to sex adults and nestlings in the field is valuable for studies of dispersal, survival, and behavior.

We developed and tested a 10-min call-broadcast survey protocol using conspecific vocalizations to assess Peregrine Falcon (Falco peregrinus) territory occupancy in the Mojave Desert of southern Nevada and northwestern Arizona from 2008–10. Response rate of peregrines, when adults were confirmed present immediately prior to broadcasting, averaged 83% during the breeding season and peaked at 100% during the courtship stage. Detection trials conducted at known occupied territories, when peregrine locations were unknown at the time of the broadcast, resulted in an average 78% detection rate across the breeding season, as compared to a 79% detection rate using the 4-hr default passive survey protocol from 2006–09. We detected peregrines in 42% of broadcast trials during the post-breeding period (September–October) in 2009. We did not observe differences in response rates related to time of day or distance from the broadcast point to the eyrie (85–1600 m). All peregrine responses during detection trials occurred within 300 sec after beginning the call-broadcast, and the mean duration of response by breeding stage diminished as the breeding season progressed. Response rates were similar by sex (male  =  60%, female  =  66%), but males were more likely to respond with females than alone. Peregrines often responded in the vicinity of eyries (72% of responses), a behavior we found useful for identifying eyrie ledges early in the breeding season. We found that conducting 10-min call-broadcast trials early in the peregrine breeding season at distances ≤700 m from the eyrie provided an effective means to assess occupancy.

We examined factors that might influence breeding-site selection in Ferruginous Hawks (Buteo regalis) in the Uintah Basin, Utah, an area undergoing rapid oil and gas development. We located 31 occupied nests of Ferruginous Hawk (10 during 2002, 10 during 2003, and 11 during 2004) and compared them to 32 historical nest sites of Ferruginous Hawks that were unoccupied during our study, and 32 random sites. Ferruginous Hawks selected nesting areas that were dominated by mixed desert-shrub vegetation communities with scattered Utah juniper trees (Juniperus osteosperma), higher prey abundance, and a high number of active petroleum wells. Within occupied territories, Ferruginous Hawks selected nest sites in juniper trees, on cliff ledges, or on rock pinnacles that occurred in areas with higher prey abundance, close to an active well, and within 2–3.5 km of the nearest occupied nest of another raptor. The counterintuitive association between nesting activity and oil development may be the result of: (1) a spurious relationship between the occurrence of oil and gas reserves and suitable breeding habitat, (2) a time lag in the response of nesting pairs to development, or (3) oil and gas developments indirectly benefiting nesting pairs by improving the habitat of prey species and subsequently increasing prey densities, and/or reducing the threat of predation to Ferruginous Hawks or their young.

The high incidence of lead exposure being reported in avian scavengers is not surprising, considering the frequency with which lead ammunition residues occur in the remains of gun-killed animals. Population impacts likely are underestimated because of latency of effect, low probability of carcass discovery, and the difficulty of detecting the health manifestations of sublethal lead burdens. There are good reasons to expect that sublethal lead is harmful, especially in view of the considerable body of human health literature providing evidence of multiple adverse effects associated with very small amounts of lead, together with the implication that lead physiology is broadly similar among vertebrates. A detailed experimental study of growth and behavior involving dosing and controls in developing Herring Gulls (Larus argentatus), and reports of morphological and physiological responses in other species, offer insight into the implications of sublethal lead exposure on wild populations. Further studies of lead's sublethal effects on avian scavengers are therefore warranted and may benefit from advancements in bone-lead measurement and feather analysis, particularly where lead burdens can be benignly assessed among live birds in the field.

Brown Falcons (Falco berigora) are generalist predators that take prey from a range of different taxonomic groups. Further, this species is one of the most widespread raptors in Australasia, providing great scope for dietary flexibility. However, few studies have reported on the diet of this species, and none in any detail for the relatively dry, continental climate of the Canberra region of southeastern Australia. We therefore examined this species' diet from 29 collections of prey remains and pellets from 20 nesting territories over five breeding seasons of Brown Falcon pairs breeding within 40 km of Canberra in 2002–06 and again in 2009. A total of 307 prey items was recorded, 15 of which were novel for this species. These novel prey items largely reflected locally common species that were of a similar size and niche to prey previously recorded in other regions, such as a new prey species of quail or beetle. Unusual prey included garden snails (Helix aspersa) and an owl, the Southern Boobook (Ninox novaeseelandiae). Other infrequently captured prey items such as freshwater molluscs (Corbicula australis and Glyptophysa gibbosa) and crayfish (Cherax sp.) illustrated the extraordinary dietary flexibility of Brown Falcons. In comparison with previous detailed studies, Canberra-based pairs had a relatively small geometric mean prey weight of 7.7 g, and tended to take a higher proportion of invertebrates across a relatively narrow niche breadth. When biomass was considered, rabbits (Oryctolagus cuniculus) were an important food source, making up half of the total biomass in the diet.