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We compared migrating behavior of Broad-winged Hawks (Buteo platypterus) at two sites along their migration corridor: Hawk Mountain Sanctuary in eastern Pennsylvania and the Kekoldi Indigenous Reserve in Limon, Costa Rica. We counted the number of times focal birds intermittently flapped their wings and recorded the general flight type (straight-line soaring and gliding on flexed wings versus circle-soaring on fully extended wings). We used a logistic model to evaluate which conditions were good for soaring by calculating the probability of occurrence or absence of wing flaps. Considering that even intermittent flapping is energetically more expensive than pure soaring and gliding flight, we restricted a second analysis to birds that flapped during observations, and used the number of flaps to evaluate factors influencing the cost of migration. Both the occurrence and extent of flapping were greater in Pennsylvania than in Costa Rica, and during periods of straight-line soaring and gliding flight compared with circle-soaring. At both sites, flapping was more likely during rainy weather and early and late in the day compared with the middle of the day. Birds in Costa Rica flew in larger flocks than those in Pennsylvania, and birds flying in large flocks flapped less than those flying alone or in smaller flocks. In Pennsylvania, but not in Costa Rica, the number of flaps was higher when skies were overcast than when skies were clear or partly cloudy. In Costa Rica, but not in Pennsylvania, flapping decreased as temperature increased. Our results indicate that birds migrating in large flocks do so more efficiently than those flying alone and in smaller flocks, and that overall, soaring conditions are better in Costa Rica than in Pennsylvania. We discuss how differences in instantaneous migration costs at the two sites may shift the species' migration strategy from one of time minimization in Pennsylvania to one of energy minimization in Costa Rica. Received 15 November 2005, accepted 8 July 2006., Each year, more than one million Broad-winged Hawks (Buteo platypterus) make a round-trip migration of 6,000-10,000 km along the Mesoamerican Land Corridor when traveling between their North American breeding grounds [...]

Although adult plumage in Cooper's Hawks (Accipiter cooperii) exhibits little of no sexual dichromatism, iris color reportedly changes from yellow or light orange in younger birds to shades of orange of red in older birds, especially in males. However, there is little quantitative data on this phenomenon. It has been suggested that male eye color may serve as a signal of age and hence reproductive fitness and thus offer a basis for nonrandom mating in Cooper's Hawks. In this study we examine the relationships between eye color and age, sex, and reproductive output for Cooper's Hawks in two breeding populations in British Columbia and North Dakota, 1999-2002, and compare these results to those previously published for a breeding population in Wisconsin, 1980-1995. Cooper's Hawks in British Columbia and North Dakota appear to acquire darker orange or red irides more frequently and more quickly than their counterparts at known and relative ages in Wisconsin. Females in all study sites are slower and less likely than males to acquire the darkest eye colors. Eye color is not a reliable predictor of age in individual male and female Cooper's Hawks, for researchers and perhaps for the birds themselves, because individual hawks of a given eye color displayed variation in known and relative ages in British Columbia and Wisconsin. There was no significant relationship between the eye color of males and their brood sizes in any of these three populations, and therefore no discernable support for the premise that male eye color per se signals male fitness, or functions as a sexual trait for assortative mating in this species. Received 20 January 2003, accepted 3 June 2003., In the Cooper's Hawk (Accipiter cooperii), a species with little or no sexual dichromatism in adult plumage (Rosenfield and Bielefeldt 1993), iris color shows an age dependent relationship, especially in [...]

During spring 2000, we captured five adult female Broad-winged Hawks (Buteo platypterus) in northcentral Minnesota and western Maryland and fitted them with satellite-received radio tags. The migrating hawks left their nesting areas about 10-15 September and moved south toward eastern Texas. They followed the Gulf Coast through Mexico and an inland course through Central America to their wintering areas. Mean fall migration distance for four hawks was about 7,000 km, and for three hawks the mean fall migration time was about 70 days and mean fall migration rate was about 100 kin/day. Three hawks arrived on their wintering areas from about 15 October to 15 December. Wintering areas tot four hawks were in Panama, Venezuela, Brazil, and Peru, between 08° 25' N, 80° 54' W and 11° 00' S, 67° 07' W. We tracked one hawk for her entire spring migration, and two hawks showed fidelity to their nest areas. Received 5 October 2002, accepted 17 March 2003., Little information has been published about migration routes, timing, or wintering sites of the Broad-winged Hawk (Buteo platypterus; Goodrich et al. 1996). Observational and banding return data show that the [...]

We used radio-telemetry to track movements of seven adult male Ferruginous Hawks (Buteo regalis) in southcentral Washington. Home range size was estimated for each male using minimum convex polygon, harmonic mean, adaptive kernel, and fixed kernel-based methods. Minimum convex polygon and harmonic mean home ranges were significantly larger than those previously reported for Ferruginous Hawks. Home ranges varied substantially among males (mean = 90.3 [km.sup.2], range = 17.7-136.4 [km.sup.2]). There was no relationship between home range size and brood size; however, there was a significant relationship ([r.sup.2] = 0.964, P = 0.018) between home range size and the distance from the nest site to the nearest irrigated agricultural field where some males hunted. Kernel-based estimates showed two distinct core areas for most males, one around the nest and a second in the agricultural fields where they hunted., The Ferruginous Hawk (Buteo regalis) is a large grassland raptor that breeds in the shrub-steppe and semi-arid regions of western North America (Olendorff 1993). The species is thought to be [...]

MARY ANNE MCLEOD [1,4] B. ANN BELLEMAN [1,5] ABSTRACT.--We evaluated characteristics at Red-shouldered Hawk (Buteo lineatus) nest sites at two study areas with different topography and forest types in north-central [...]

HELMUT C. MULLER [1,2,4] NANCY S. MUELLER [2] DANIEL D. BERGER [2] GEORGE ALLEZ [2] WILLIAM ROBICHAUD [2] JOHN L. KASPAR [2,3] ABSTRACT.--We trapped more than 23,000 migrating raptors at [...]

PAMELA C. RASMUSSEN [1] ABSTRACT.--A distinctive new species of hawk-owl, Ninox ios, is described from a specimen collected in 1985 in forest at 1120 m in Bogani Nani Wartabone (then [...]

Swainson's Hawks (Buteo swainsoni; Aguilucho Langostero) were captured and banded in La Pampa, Argentina from 28 November 1996 through 25 January 1997. We collected morphometric measurements to determine if hawks gained weight on the austral (non-breeding) grounds. Hawks in apparently healthy condition weighed 819.7 ± 11.1 g (mean ± SE, n = 127, range 540-1090 g). Weight increased significantly over the length of the non-breeding season in Argentina (P = 0.0059), but wingspan (124.9 ± 0.5 cm, n = 127, range 105.7-137.1 cm) and tail (19.8 ± 0.1 cm, n = 127, range 16.5-23.1 cm) did not. When separated by age, weight increased significantly for juveniles (P = 0.0083) but was marginally non-significant for adults (P = 0.0555)., Swainson's Hawks (Buteo swainsoni) are long-distance migrants that travel between the plains, shrublands, and pampas (grasslands) of North and South America. During the southward migration, some hawks temporarily stop in [...]

ALL WEATHER HAWK WATCHER'S FIELD JOURNAL. By Donald S. Heintzelman. J. L. Darling Corp., Tacoma, Washington. 2002:64 pp. $7.95 (spiral bound, plastic cover).--I was introduced to Rite-in-the-Rain all-weather field notebooks [...]

In the majority of bird species males are larger than their mates. A number of arguments have been brought to bear on this prominent among which is that competition between [...]