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Cooper's Hawks (Accipiter cooperii) nest commonly in various habitats throughout North America, but there are few comparative studies of the ecology of urban vs. rural nesting birds, especially regarding 1 v olds whose inexperience is purported to place them under different selective pressures than more commonly nesting hawks [greater than or equal to] 2 y of age. Notably, selective pressures of cities have prompted recent changes in the life histories and phenotypes of urban birds, and some of these pressures may be age dependent. We investigated select intrinsic properties of individuals and reproductive output of breeding yearling females and their mates for potential differences in the ecology of urban vs. rural birds in Wisconsin, 1980-2017. We found no differences in mean body mass of yearling females, their male mates, nesting phenology, nor in average clutch or brood counts in urban vs. rural Cooper's Hawks. Excluding one instance, yearling females were mated to older males, [greater than or equal to] 2 y of age, and within 33 pairs birds mated by like sizes (small/small. etc.). Sums of masses for paired birds were not correlated with their brood sizes, in contrast to our earlier findings on the same study areas where brood size was positively' and significantly correlated with summed masses of paired birds [greater than or equal to] 2 y old who also mated by similar size. We call for more comparative studies of Cooper's Hawks in cities < 100,000 people as studied herein, as most research on urban nesting Cooper's Hawks stem from large, metropolitan cities with about 1 million people, which are less prevalent than smaller cities as we investigated. Indeed, there is growing evidence worldwide that the types and strength of selective pressures on urban wildlife is greater in larger cities, vet less is known about small cities., INTRODUCTION Urban populations of Cooper's Hawks (Accipiter cooperii) exhibit the highest nesting densities and many of the highest reproductive indices for the species across its broad North American range (Rosenfield [...]

We compared the pronounced geographic pattern in the recolonization of Britain by the Eurasian Sparrowhawk (Accipiter nisus) from 1970 onward with the spatiotemporal pattern among House Sparrow (Passer domesticus) populations over the same period, using data on the occurrence of both species at garden feeding stations. Using a simulation of House Sparrow population trends based on a logistic model that incorporated a predation index derived from Eurasian Sparrowhawk incidence functions, we generated a close approximation to the unique trajectories among House Sparrow populations in rural and urban sites in different regions of Britain. We carried out further comparisons using two contrasting methods that focused solely on temporal patterns. We used estimates of the varying date of Eurasian Sparrowhawk recolonization at different sites to derive time variables in relation to recolonization date. One such relative time variable proved to be a better predictor of House Sparrow numbers than chronological time; ir indicated that House Sparrow numbers were generally stable or increasing prior to recolonization by Eurasian Sparrowhawks but declined continuously afterward. We also detected a significantly greater decrease in House Sparrow numbers when Eurasian Sparrowhawks were present using a method that compared annual changes in the abundance of prey species in the presence or absence of a predator. On the basis of these results, we argue that predation by Eurasian Sparrowhawks may be a sufficient explanation for the decline in House Sparrows in Britain. We also argue that urban House Sparrow populations' long-term release from predator pressure made them especially vulnerable when urban habitats were colonized by Eurasian Sparrowhawks. Received 3 April 2009, accepted 31 October 2009. Key words: Accipiter nisus, blitzkrieg hypothesis, Eurasian Sparrowhawk, House Sparrow, Passer domesticus, population limitation, predator--prey interaction, songbird declines, urban ecology. Nous avons compare le patron geographique de la recolonisation de la Grande-Bretagne par Accipiter nisus depuis 1970 et le patron spatiotemporel des populations de Passer domesticus au cours de la meme periode, a partir de donnees sur la presence des deux especes a des mangeoires. A l'aide d'une simulation des tendances des populations de P. domesticus basee sur un modele logistique incorporant un indice de predation derive de fonctions d'incidence de A. nisus, nous avons genere une bonne approximation des trajectoires uniques des populations de P. domesticus dans des sites ruraux et urbains de differentes regions de Grande-Bretagne. Nous avons effectue des comparaisons plus poussees a l'aide de deux methodes opposees qui portaient uniquement sur les patrons temporels. Nous avons utilise des estimations de la date de recolonisation d'A. nisus a differents sites pour deriver des variables temporelles. L'une de ces variables s'est averee etre un meilleur indice de l'abondance de P. domesticus que le temps chronologique; elle a indique que le nombre de P. domesticus etait generalement stable ou augmentait avant la recolonisation par A. nisus mais diminuait regulierement par la suite. Nous avons aussi detecte une baisse signincativement plus importante du nombre de P. domesticus lorsque A. nisus etait present, en utilisant une methode qui comparait les variations annuelles de l'abondance de l'espece-proie en presence ou en l'absence d'un predateur. Sur la base de ces resultats, nous croyons que la predation par A. nisus peut expliquer le declin de P. domesticus en Grande-Bretagne. Nous soutenons egalement que le relachement a long terme de la pression de predation sur les populations urbaines de P. domesticus les a rendues particulierement vulnerables lorsque les habitats urbains etaient colonises par A. nisus. DOI: 10.1525/auk.2009.09108

We evaluated the influence of weather on reproduction of the Red-shouldered Hawk (Buteo lineatus) in an agricultural landscape in south-central Florida where we found relatively high densities of successfully nesting hawks. We used a generalized linear modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the timing of nesting, nesting success, and productivity of hawks during 1995-2000. The best models indicated an influence of rainfall frequency and laying period on hawk reproduction. During years with less frequent rainfall in the summer and fall months prior to the beginning of the breeding season, fewer pairs attempted to nest, and hawks nested later and had smaller clutch sizes and lower productivity. Hawks that nested later in the breeding season had lower hatching success and lower overall nest success. Although Red-shouldered Hawks are generally reported to inhabit forested landscapes throughout their range, a common feature seems to be a dependence on wetlands and riparian habitat for foraging. We propose that the proportion of wetlands throughout the landscape is a unique aspect of south-central Florida that may allow for persistence of unusually high numbers of hawks. Key words: agriculture, Florida, nest success, productivity, rainfall, raptor, Red-shouldered Hawk. Evaluamos la influencia del clima en la reproduccion de Buteo lineatus en un paisaje agricola en el centro-sur de Florida, donde encontramos densidades relativamente altas de aguiluchos de esta especie nidificando exitosamente. Empleamos un enfoque estadistico de modelos lineales generalizados dentro del marco de la teoria de la informacion para examinar la influencia de la precipitacion total, la frecuencia de precipitacion y la temperatura en las fechas de nidificacion sobre el exito de nidificacion y la productividad de los aguiluchos entre 1995 y 2000. Los mejores modelos indicaron una influencia de la frecuencia de la precipitacion y del periodo de puesta sobre la reproduccion de los aguiluchos. Durante los anos con precipitaciones menos frecuentes durante el verano y los meses de otono anteriores al comienzo de la estacion de cria, un menor numero de parejas intentaron nidificar, y estas nidificaron mas tarde y tuvieron tamanos de nidada menores con una menor productividad. Los aguiluchos que nidificaron mas tarde en la estacion reproductiva presentaron un exito de eclosion menor y un exito general de nidificacion menor. A pesar de que generalmente se informa que B. lineatus habita paisajes boscosos a lo largo de su rango de distribucion, una caracteristica comun parece ser la dependencia de los humedales y ambientes riberenos para forrajear. Proponemos que la alta proporcion de humedales a lo largo del paisaje es una caracteristica unica del centro-sur de Florida, lo que podria permitir la persistencia de densidades inusualmente altas de aguiluchos.

The Red-shouldered Hawk call-broadcast survey conducted in Central Minnesota, USA, was analyzed by using maximum-likelihood models to estimate their occupancy and detection probability. Estimates were found similar with different sampling strategies such as double and discontinued sampling and varied in number of sample locations.

A breeding Cooper's hawk population in the urban Milwaukee area, Wisconsin, U.S., is studied over a 12-year period and their reproductive success, age structure, nest-site occupancy and natal dispersal are documented. The study has shown that these nesting areas were not marginal or inferior habitats and that urban Cooper's hawks were not a sink population.

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 [...]

Because of their smaller size and isolation, island populations tend to be more divergent and less genetically variable than mainland populations. We collected DNA samples from nine Galapagos Hawk (Buteo galapagoensis) island populations, covering the species' entire range. Neutral minisatellite DNA markers were used to calculate within-island genetic diversity and between-island genetic differentiation ([F.sub.ST]). Typically, these markers mutate too quickly to be informative in such studies. However, in very small, isolated populations, concerns about high mutational rate are obviated by the relative force of genetic drift. Individuals within islands had the highest levels of reported genetic uniformity of any natural bird population, with mean within-population band-sharing similarity values ranging from 0.693 to 0.956, increasing with decreasing island size. Galapagos Hawks exhibit cooperative polyandry to varying degrees across islands; however, we did not find an association between degree of polyandry and genetic variability. Between-island [F.sub.ST] values ranged from 0.017 to 0.896, with an overall archipelago value of 0.538; thus, most populations were genetically distinct. Also, we documented higher levels of genetic similarity between nearby populations. Our results indicated negligible gene flow among most Galapagos Hawk populations, and genetic drift has played a strong role in determining structure at these minisatellite loci. Received 16 April 2004, accepted 5 April 2005. Key words: Buteo galapagoensis, cooperative polyandry, Galapagos Hawk, Galapagos Islands, genetic drift, minisatellites.

We tested for associations between body condition, territory ownership, and permanent parasite load of Galapagos Hawks (Buteo galapagoensis) on Isla Marchena, Galapagos. Two louse species were collected from most of the 26 hawks sampled: the amblyceran Colpocephalum turbinatum and the ischnoceran Degeeriella regalis. Nonterritorial hawks were in significantly poorer body condition than territorial hawks. Body condition was negatively correlated with the abundance of C. turbinatum. Nonterritorial hawks had significantly higher mean abundances, mean intensities, and median intensities of both louse species than territorial hawks. The amblyceran's mean abundance and intensity were significantly higher than the ischnoceran's. Abundances of the two lice were positively related when the population size of C. turbinatum was 100 individuals. Parasite load and body condition both predicted territory ownership well. Key words: body condition, ectoparasite, Falconiformes, Galapagos, Phthiraptera, territoriality.

Previous interspecific studies have shown that migratory birds have a higher prevalence of blood parasites than nonmigratory birds. It is thought that birds that move greater distances are exposed to a larger parasite fauna, because of uneven distribution of vectors that carry such parasites. Current hypotheses also suggest that the stress of migration may allow parasites to persist, by weakening the immune system and allowing latent infections to recur. We captured migrating hatching-year Sharp-shinned Hawks (Accipiter striatus) in New Mexico and estimated natal latitudes of each individual by analyzing stable-hydrogen isotope ratios of feathers. That enabled us to estimate distances traveled up to point of capture. We also collected blood to quantify hematozoan infection prevalence and intensity. We related distance traveled to prevalence and intensity of hematozoan infections. Contrary to previous hypotheses, our results show no relationship between distance traveled by migrants and prevalence and intensity of hematozoan infections. Of 75 individuals examined, 24% were infected with Leucocytozoon toddi, 37% with Haemoproteus elani, and 5% with H. janovyi. To our knowledge, this is the first documented occurrence of H. janovyi in North America and in Sharp-shinned Hawks. Our stable-hydrogen isotope analyses indicated that H. janovyi was detected only in birds that originated in southwestern North America, which may be of significance in regard to biogeography of that parasite species.

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 [...]

Hydrogen stable-isotope analysis of feathers is an increasingly popular method for estimating the origins of migrating and wintering birds. Use of this method requires that investigators know which feathers are grown on breeding grounds and how the hydrogen stable-isotope ratios of feathers ([delta][D.sub.f]) relate to those of local precipitation ([delta][D.sub.p]). In this study, we measured [delta][D.sub.f] of adult (primaries 1, 3, and 10) and nestling Cooper's Hawks (Accipiter cooperii) in Wisconsin, North Dakota, and British Columbia, Canada. As previously shown, [delta][D.sub.f] of nestling feathers were related to [delta][D.sub.p]. In contrast, the [delta][D.sub.f] of adult feathers grown on the breeding grounds were substantially greater than those of their nestlings, and varied significantly across primary feathers and study areas. Our findings suggest that it is not possible to use hydrogen stable-isotope analysis of feathers to learn the origins of migrating adult Cooper's Hawks (or possibly adults of other large-bodied species with extended molting periods) until more is learned about the physiological or ecological mechanisms underlying these isotopic discrepancies. Key words: Accipiter cooperii, migration, molt, raptor.

We examined the predatory behavior of wintering urban Cooper's Hawks (Accipiter cooperii). Eight Cooper's Hawks (7 female, 1 male) were radio-tracked intensively during two winter periods from 1999-2001. We observed 179 attacks, 35 of which were successful, for an overall attack success rate of 20%. We recorded an additional 44 kills resulting from unobserved attacks. European Starlings (Sturnus vulgaris), Mourning Doves (Zenaida macroura), and Rock Doves (Columba livia) made up 95% of the prey attacked and 91% of the diet. Smaller birds ( Key words: Accipiter, hawks, hunting behavior, predator-prey interactions, safety in groups, urban environment, wintering birds.

Interspecific variation in sexual size dimorphism has commonly been attributed to variation in social mating system, with dimorphism increasing as intrasexual competition for mates increases. In birds, overall body size has also been found to correlate positively with size dimorphism. In this study, we describe variation in morphology and mating system across six populations of the endemic Galapagos Hawk (Buteo galapagoensis). Galapagos Hawks exhibit cooperative polyandry, a mating system in which long-term social groups contain a single female and multiple males. Comparisons among islands revealed significant differences in overall body size for both adults and immatures. Populations ranged from completely monogamous to completely polyandrous, with varying mean group sizes. Data did not support our prediction that sexual size dimorphism would increase with the degree of polyandry (number of males per group) or with body size; there was no correlation between mating system and sexual dimorphism. We did find a significant negative relationship between degree of polyandry and body size among islands, opposite of the pattern predicted. Key words: body size, Buteo galapagoensis, cooperative polyandry, Galapagos Hawk, principal components analysis, sexual size dimorphism.

The risk to passerine birds of predation by the Sparrowhawk (Accipiter nisus) was analyzed with respect to differences in plumage brightness, body mass, and density of prey species, while taking into account phylogenetic relatedness of species. Data were collected from published sources in five separate areas along a south-north geographical gradient in Finland and consisted of 2214 prey remains collected from Sparrowhawk nests. Prey plumage brightness was the most important factor determining vulnerability to predation. In adults, male brightness was more important than female brightness in explaining prey vulnerability. Prey abundance did not affect the relationship between predation vulnerability and plumage brightness, because both rare and common species with bright plumage suffered higher predation. Prey species with large body mass were more vulnerable to predation in northern Finland, suggesting that in northern harsh conditions, Sparrowhawks may prefer large prey in order to fulfill their daily energy requirements. Our analyses provide evidence that predation may impose viability costs on sexually selected traits such as plumage brightness and body size. Key words: Accipiter nisus; body mass; Finland; latitude gradient; passerines; plumage brightness; predation risk; prey density; sexual selection; Sparrowhawk.

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 [...]

Age-related trends in breeding performance of female Eurasian Sparrowhawks (Accipiter nisus) were examined in south Scotland. Over a 22 year period, most individuals were banded and of known age. Previous analyses had shown that average number of young raised per breeding attempt (or year) increased progressively in successive age-groups to midlife (around five years) and declined thereafter. Here we analyze different components of breeding performance (such as clutch-size, hatching and fledging success) to find which components contribute most importantly to the overall age-related trend in productivity. Most aspects of breeding showed a similar upward-downward trend through the life span, but the downward trend in productivity in later life could be attributed mainly to poorer nestling survival. In general, in each aspect of breeding, the mean trend of the population as a whole was followed by individuals studied at different ages. Such individual trends were sufficient to account for the overall mean trend, and there was no need to postulate that high-performance or low-performance birds entered and left the breeding population at different ages. Only one aspect of breeding showed no trend with age, namely proportion of birds that laid having built a nest, but that type of failure affected only a small proportion of individuals. Received 23 August 2001, accepted 10 April 2002.

Research describing pair formation in Cooper's Hawks (Accipiter cooperii) is presented. In particular the breeding success of adult and subadult mixed and non-mixed pairs is investigated.

Nonrandom pairings of Wisconsin Cooper's Hawks with respect to body mass have been observed. The behavior, which include findings of a disproportionate share in the subsequent breeding population from breeding adults of higher mass, indicate a direct correlation between nonrandom pairing and recruitment among falconiform species. The breeding behavior is explained through such factors as territory quality and the differential timing of migration patterns.

Cooper's hawks in Tucson, AZ, and in exurban areas in the southeastern part of the state were studied from 1994 to 1996 to compare their breeding ecology and productivity, with the end in view of assessing the quality of an urban environment as habitat for a species. Nesting was earlier for urban pairs and their clutches larger than exurban pairs. Urban nests were also found to have higher nesting mortality, with trichomoniasis as the primary cause of death. Urban nests also had a greater overall failure rate than exurban nests.

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 [...]

The offspring sex ratios for Cooper's Hawk were determined at 372 nests throughout Wisconsin from 1980 to 1995. The results revealed no significant differences in sex ratios at fertilization and at the nestling stage. However, the males were significantly more numerous at both stages, indicating that sex ratios at the fertilization and nestling stages were skewed toward males.

Recent research has assessed whether red-shouldered hawks and Cooper's hawks living in mainly wooded areas respond equally well to pre-recorded vocalisations of great horned owls as to vocalisations of each conspecific calls. It was found that response patterns do not vary between each type of vocalisation. This result has a number of implications for wildlife management, indicating that using pre-recorded vocalisations of great horned owls can increase detection of woodland hawks during breeding season surveys.

A nesting habitat study was conducted to examine the relationship between accipiter size and the structural size of their nest trees and sites. The inverse correlation between the bird's body size and tree density, basal area and percent canopy closure is also evaluated. Only nest tree height and nest tree dbh showed correlation with body size. All accipiter species also preferred conifer and conifer/aspen forest for nesting habitat.

Female willow tits reduce their defense intensity directly in proportion to the closeness of their nests to the nearest sparrowhawk nest. It is clear in terms of spatial arrangement that tits breeding close to sparrowhawk nests face hawks more regularly than tits breeding further away. The distinct nature of the responses to the sparrowhawk nest distance was corroborated by the control experiment. There is no dependency on hawk-nest distance in responses towards stoats.

The individual andintersexual variations in the vocalizations of White-tailed hawks were studied.Alarm calls from six resident breeding adult hawks at the Attwater Prairie Chicken National Wildlife Refuge were recorded for a duration of five days. Sonograms of the recorded calls are then generated and measured using a computer software package. Results reveal strong variations in the individual and intersexual calls of the White-tailed Hawks.

The ability of free-ranging Common Nighthawks to enter torpor was evaluated. Nighthawks were captured by mist nets from the vicinity of Okanagan Falls in British Columbia and were subsequently weighed using an electronic balance. Thehawks' skin temperature was checked and recorded every 20 minutes between sunset and sunrise to determine the onset of torpor. Results revealed that Common Nighthawks are not physiologically adapted to enter torpor as a means ofenergy conservation.