The striking black and white plumage of the juvenile Golden Eagle (Aquila chrysaetos) provides an excellent opportunity to examine the possible selective forces influencing the strategic placement of dark pigment in birds. The conflict between opposing selective pressures (first, toward large white patches, which may allay aggression in adults, and second, toward dark plumage to promote camouflage and limit solar and abrasive wear) provides the stage whereon are revealed a score of pigmentation traits of potential adaptive value.

The general pigmentation trend is for zones that are more exposed to the sun to be darker than elsewhere. More specifically: (1) for rectrices and remiges, outer webs are darker than inner; (2) for those few feathers (e.g., central rectrices, some scapulars, and some tertials), where both inner and outer webs are heavily and nearly equally solar exposed, pigmentation is supplied similarly on both webs; (3) outermost primaries and rectrices are darkest of all and are structurally similar; (4) for central rectrices, subject to high levels of abrasion with substrate, the tip is paler (resultant flexibility may limit breakage); and (5) pigment is heavier along or on the rachis than on the webs.

Many of the traits listed above for the Golden Eagle are also found in other families of birds. Traits of the tail common to many species were a terminal pale tip, a subterminal dark band, rachis darker than vane, and outer webs darker than inner for both remiges and rectrices. The most widespread traits likely have adaptive value.

We investigated lifetime reproductive success (LRS) of 22 male and 46 female adult Flammulated Owls (Otus flammeolus) in Colorado from 1981–2003. Sexual differences in LRS were at least partially attributable to incomplete breeding histories of females, due to females having a higher estimated emigration rate from the study area than males. The mean number of lifetime breeding attempts for males was 3.4 ± 0.6 (SE; range  =  1–12), and for females it was 1.9 ± 0.3 (range  =  1–8). Adjusted for emigration beyond the study area, the estimated mean number of lifetime breeding attempts was 3.6 for males and 2.5 for females. The mean number of lifetime successful breeding attempts (fledging at least one owlet) was similar to lifetime breeding attempts for each sex, reflecting the fact that 84% (85 of 101) of all breeding attempts were successful. Breeding lifespan was correlated with lifetime reproduction for both sexes. Males tended nests that produced 6.9 ± 1.2 fledglings over 4.3 ± 0.8 yr, while females produced 4.0 ± 0.6 fledglings over 2.0 ± 0.3 yr; adjusted for emigration beyond the study area, males tended nests that produced 7.2 fledglings over 4.5 yr, while females produced 5.2 fledglings over 2.6 yr. Relatively few individuals of each sex produced most of the offspring, as 18% of females and 24% of males produced 50% of total owlets. Our finding that relatively few adults accounted for most offspring appears to be associated with habitat quality in territories. Flammulated Owls tend to have a life-history strategy similar to larger raptors by having a relatively low annual reproductive rate and a relatively long lifespan.

Red-tailed Hawks (Buteo jamaicensis) have expanded their range as trees have invaded formerly-open grasslands. Desert grasslands of southern Arizona have been invaded by mesquite trees (Prosopis velutina) since Anglo-American settlement and now support a large population of Red-tailed Hawks. We studied a population of Red-tailed Hawks in an altered desert grassland in southern Arizona. Our objectives were to determine what environmental characteristics influence Red-tailed Hawk habitat selection in mesquite-invaded desert grasslands and to evaluate the habitat quality of these grasslands for Red-tailed Hawks based on nesting density, nest success, and productivity. Red-tailed Hawks had 86% (95% C.I.  =  73–99) nest success and 1.82 young per breeding pair (95% C.I.  =  1.41–2.23). Nesting density was 0.15 (95% CI  =  0.08–0.21) breeding pairs/km² and the mean nearest-neighbor distance was 1.95 km (95% C.I.  =  1.74–2.16). Red-tailed Hawks selected nest-sites with taller nest-trees and greater tree height and cover than were available at random. Mesquite trees in desert grasslands provide abundant potential nesting structures for Red-tailed Hawks.

Descriptions of landscape characteristics of Golden Eagle (Aquila chrysaetos) nesting territories and foraging areas in Alaska are generally broad and qualitative. To provide a basis for future studies on relationships between landscape characteristics and reproductive success, we described landscape characteristics within a 3000-m radius surrounding the geographic center of 36 Golden Eagle nesting territories in Denali National Park and Preserve, Alaska. Within the 3000-m territory cores, we delineated 27 unique land-cover types based on 11 unique types of vegetation cover and structure within four terrestrial physiographic zones: Alpine, Upland, Lowland, and Riparian. Rugged terrain, alpine areas, and a mosaic of land-cover types including Alpine Low Shrub, Alpine Barren, Upland Low Shrub, Riparian Barren, and Riparian Shrub characterized most territory cores. Alpine was the most common physiographic zone, and low shrub was the most common land-cover type in territory cores (x  =  68.5% area, 95% C.I.  =  61.2–75.5%). Our results should be useful for monitoring responses of breeding Golden Eagles to future changes in this landscape.

The occurrence of Grey-faced Buzzard (Butastur indicus) in central Japan was studied in the 1970s and 1990s. There was a significant decline in the number of Grey-faced Buzzards sighted; from 28 survey squares in the 1970s to zero in the 1990s. In the Tokyo areas, the amount of edge between forests and paddy fields, which was probably an important habitat for the buzzard, was markedly decreased from 1.1 ± 1.5 km in the 1970s to 0.3 ± 0.6 km in the 1990s. The decline of Grey-faced Buzzards breeding in the Tokyo region probably was caused by the habitat loss resulting from abandonment or development of traditional paddy fields (yatoda). These human modifications probably reduced populations of suitable prey.

When adult, the gender of Western Marsh Harriers (Circus aeruginosus) is determined on the basis of the presence of gray feathers on the wing and on the tail in the males. However, males of this species in southwestern France have female-like plumages, lacking gray feathers, and thus, gender determination is impossible by using coloration alone. We investigated sex determination using biometric parameters in a study site located in southwestern France. From one to six measurements (body mass, bill length, wing chord length, tarsus length and width, and tail length) were taken from 243 marsh harriers of known gender (156 males and 87 females), marked in the study site, and subsequently re-sighted. Additionally, 30 marsh harrier specimens were measured by two observers to establish within and between observer repeatability values, as well as within bird repeatability for the six biometric parameters. Using quadratic discriminant analysis, we showed that it was possible to sex individuals of this species with >99% accuracy on the basis of only two parameters: bill length and body mass. Actually, using bill length alone provides very good indication of gender (accuracy >96%). These two parameters are also those for which observer and within-bird repeatability values were highest. When we applied the discriminant equation to 648 fledged birds that have been captured so far, the adult sex ratio (percent of males) was 49.1, which did not depart from parity.

Food habits of the Red-backed Hawk (Buteo polyosoma) were studied in the southeastern coast of Buenos Aires Province, Argentina, during autumn and winter of 2001–03. At the study area, the Red-backed Hawk was a specialist predator. On a numerical basis, 99.5% of its prey were small mammals, and little seasonal and annual variability in diet was observed. The diet was composed of murids—mainly field mice (Akodon azarae), pampas rice rats (Oligoryzomys flavescens), and vesper mice (Calomys spp.), and by octodontids (tuco-tucos [Ctenomys talarum]). The tuco-tuco was the most important prey, representing 55% of the diet biomass. The Red-backed Hawk exhibited a sit-and-wait strategy, indicated by the high percentage of time study birds were perched (78.8%). Feeding, comfort movements, and flight were also recorded (11.6%, 4.9%, and 4.7%, respectively). We observed 61 capture attempts on tuco-tucos, of which 42.6% were successful. Hawks displayed agonistic interactions with other bird species. The main aggressor (77.5%, N  =  372) was the Chimango Caracara (Milvago chimango) that frequently consumed prey remains discarded by the hawks. Our work suggests a trend of preying on relatively more small mammals toward the southern end of its geographic range. The Red-backed Hawk in its wintering range seems to be a relative specialist predator mostly employing passive search as its main hunting strategy.