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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 [...]