Social monogamy is the prevalent mating system in birds, but alternative strategies of extra-pair paternity (EPP) and conspecific brood parasitism (CBP) occur in many species. Raptors are virtually absent in discussions of broad taxonomic reviews regarding EPP and CBP likely because these strategies are mostly absent or at low frequency; CBP is unreported in solitary nesting raptors. In contrast, we found high frequencies of EPP (16%-31%) and CBP (15%-26%) nests among three populations of Cooper's Hawks (Accipiter cooperii) across the northern breeding range of this solitary nesting, socially monogamous species. EPP and CBP combined occurred in 42%-46% of all nests among populations and hence unexpectedly were nearly equivalent to proportions of genetically monogamous nests. Select covariates failed to predict presence of EPP and CBP in part because virtually all extra-pair adults were uncaught and likely were floaters. We found no support for the hypothesis that territorial females traded copulations for food to maximize energy intake for increased production. Our unique discoveries enhance knowledge of the extent and diversity of alternative breeding strategies among groups of avian and other animal species.

We discuss select imprecise and untenable natural history information about migration, urban habitat use, and diet presented in the technical literature about Accipiter hawks in North America. We focus primarily on challenging the claim that Sharp-shinned Hawks (Accipiter striatus) are more frequent predators of House Sparrows (Passer domesticus) than are Cooper's Hawks (A. cooperii). We urge scientists to be cognizant of the ever-changing dynamics of the predatory behavior, nesting, and migration ecology of Sharp-shinned and Cooper's hawks due to anthropogenic factors, features that are in constant flux and may not be well tracked long term or apply to the entire distributional ranges of these 2 species.

Raptors exhibit some of the highest rates of intra-pair copulations among birds, perhaps in an attempt by males to reduce the risk of being cuckolded. Indeed, the frequency of extra-pair fertilizations reported in studies of raptors to date is relatively low (0-11.2%). Socially monogamous Cooper's Hawks (Accipiter cooperii) exhibit one of the highest copulation rates among birds, yet there are no published accounts of extra-pair copulations (or paternity). We studied a population of Cooper's Hawks in Milwaukee, Wisconsin, during three breeding seasons (2003, 2004, and 2007), examining the possible effects of age (1 yr old vs. 2 yr old), adult mass, and brood size on the frequency of extra-pair paternity (EPP). We found that 19.3% of nestlings (N = 27/140) were extra-pair young (EPY), and 34% of all broods (N = 15/44) had at least one EPY. The sires of the EPY in our study were identified for only two broods, suggesting that floater males may have engaged in extra-pair copulations with territorial females. We found that brood size was a good predictor of the occurrence of EPP (EPP) in nests, but adult mass and female age were not. To our knowledge, these possible correlates of the occurrence of EPP in raptors had not previously been investigated. Male Cooper's Hawks provide food for females during the pre-nesting period, and delivery of food is, in contrast to other raptor species, typically followed by copulation. Thus, one possible explanation of the relatively high rates of EPP in our study is that females might accept or even solicit extra-pair copulations from males other than their mates as a means of maximizing energy intake for egg production. Such behavior might be particularly likely in our study area, i.e., a food-rich urban setting with a high breeding density of Cooper's Hawks.RESUMEN Alta frecuencia de paternidad con mas de una hembra en una poblacion urbana de los halcones de Cooper Entre las aves, los rapaces machos presentan algunas de las tasas mas altas de copulacion con mas de una hembra, tal vez en un intento de los machos para reducir el riesgo de ser enganado. De hecho, la frecuencia de fertilizaciones con mas de una hembra reportado en estudios de rapaces hasta hoy en dia es relativamente baja (0 - 11.2%). Halcones de Cooper (Accipiter cooperii) son socialmente monogamos y presentan una de las tasas mas altas de copulacion entre las aves, sin embargo, no hay cuentas publicadas de copulas fuera de la pareja (o paternidad). Se estudio una poblacion de halcones de cooper en Milwaukee, Wisconsin, durante tres temporadas de cria (2003, 2004, y 2007). Examinamos los efectos posibles de la edad (un ano de edad hasta dos anos de edad), la masa corporal de adultos, y el numero de pollos en el nido contra la frecuencia de paternidad con mas de una hembra. Se encontro que el 19.3% de los polluelos (N = 27/140) eran de una pareja en que el macho copulo con mas de una hembra (EPY), y el 34% de todos los nidos (N = 15/44) tuvieron al menos una EPY. Se identificaron los padres de la EPY en nuestro estudio para solo dos crias, lo que sugiere que los machos flotantes (aparean con mas de un individuo) pudieron haber participado en copulaciones con mas de una hembra territorial. Se encontro que el tamano de la nidada fue un buen factor predictivo de la incidencia de la EPP en los nidos, pero la masa corporal de los adultos y la edad de la hembra no fueron factores importantes. A nuestro entender, no han hecho investigaciones de estos correlatos en la ocurrencia de EPP en rapaces. Los machos de los halcones de Cooper proporcionan alimento para las hembras durante el periodo previo a la anidacion, y la entrega de alimentos es normalmente seguida por la copulacion, lo cual es en contraste de otras especies de rapaces. Por lo tanto en nuestro estudio, una posible explicacion de relativamente altas tasas de paternidad con mas de una hembra, es que las hembras pueden aceptar o incluso solicitar EPCs de machos que no son sus companeros como un medio para maximizar el consumo de energia para la produccion de huevos. Tal comportamiento puede ser particularmente probable en nuestra area de estudio, es decir, un entorno urbano rico en alimentos con una alta densidad de cria de halcones de Cooper.

Abstract Offspring sex ratios at the termination of parental care should theoretically be skewed toward the less expensive sex, which in most avian species would be females, the smaller gender. Among birds, however, raptors offer an unusual dynamic because they exhibit reversed size dimorphism with females being larger than males. And thus theory would predict a preponderance of male offspring. Results for raptors and birds in general have been varied although population‐level estimates of sex ratios in avian offspring are generally at unity. Adaptive adjustment of sex ratios in avian offspring is difficult to predict perhaps in part due to a lack of life‐history details and short‐term investigations that cannot account for precision or repeatability of sex ratios across time. We conducted a novel comparative study of sex ratios in nestling Cooper's hawks (Accipiter cooperii) in two study populations across breeding generations during 11 years in Wisconsin, 2001–2011. One breeding population recently colonized metropolitan Milwaukee and exhibited rapidly increasing population growth, while the ex‐Milwaukee breeding population was stable. Following life‐history trade‐off theory and our prediction regarding this socially monogamous species in which reversed sexual size dimorphism is extreme, first‐time breeding one‐year‐old, second‐year females in both study populations produced a preponderance of the smaller and cheaper sex, males, whereas ASY (after‐second‐year), ≥2‐year‐old females in Milwaukee produced a nestling sex ratio near unity and predictably therefore a greater proportion of females compared to ASY females in ex‐Milwaukee who produced a preponderance of males. Adjustment of sex ratios in both study populations occurred at conception. Life histories and selective pressures related to breeding population trajectory in two age cohorts of nesting female Cooper's hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Cooper's hawks in Wisconsin.

Cooper's Hawk (Accipiter cooperii) populations breeding in the northern portion of the species' range exhibit variation in morphological traits that conforms to predictions based on differences in prey size, tree stand density, and migratory behavior. We examined genetic structure and gene flow and compared divergence at morphological traits (P-ST) and genetic markers (F-ST) to elucidate mechanisms (selection or genetic drift) that promote morphological diversification among Cooper's Hawk populations. Cooper's Hawks appear to conform to the genetic pattern of an east west divide. Populations in British Columbia are genetically differentiated from north-central populations (Wisconsin, Minnesota, and North Dakota; pairwise microsatellite F-ST = 0.031-0.050; mitochondrial DNA Phi(ST) = 0.177-0.204), which suggests that Cooper's Hawks were restricted to at least two Pleistocene glacial refugia. The strength of the Rocky Mountains Great Plains area as a barrier to dispersal is further supported by restricted gene-flow rates between British Columbia and other sampled breeding populations. Divergence in morphological traits (P-ST) was also observed across study areas, but with British Columbia and North Dakota differentiated from Wisconsin and Minnesota, a pattern not predicted on the basis of F-ST and Phi(ST). interpopulation estimates. Comparison of P-ST and F-ST estimates suggests that heterogeneous selection may be acting on Cooper's Hawks in the northern portion of their distribution, which is consistent with hypotheses that variation in prey mass and migratory behavior among populations may be influencing overall body size and wing chord. We were unable to distinguish between the effects of genetic drift and selection on tail length in the study populations. Received 26 July 2011, accepted 20 March 2012.

Cooper's Hawks (Accipiter cooperii) have recently colonized many urban landscapes across North America, but data on breeding densities and trends in densities of these populations are lacking. We surveyed for woodland raptors throughout approximately 1000 km(2) in the metropolitan Milwaukee, Wisconsin, area over a 21-yr period, 1988-2008. We documented the natural colonization of this urban landscape by a pioneer Cooper's Hawk population and its subsequent growth from 1993-2008 (4 to 41 laying pains, 4 to 55 occupied sites). Nearest-nest distances decreased and the number of Cooper's Hawk laying pairs increased while nesting surveys remained consistent temporally and spatially, indicating that density of breeding pairs was increasing in the metropolitan Milwaukee area. Approximately 15 yr after initial colonization, the breeding density of Cooper's Hawks in some localized areas averaged one laying pair per 330 ha (range: 68-587 ha). Front 1996-2008, as breeding density increased, average annual productivity (number of young/laying pair) for Cooper's Hawks in Milwaukee County, a subset of the overall larger metropolitan study area, also increased. During the early years of colonization, a relatively high proportion of individuals or pairs of birds appeared to occupy nest sites but did not breed. Younger birds may have played a role in the colonization of this urban landscape. This population was likely increasing at a relatively rapid rate during the late 1990s and continued to increase throughout the remainder of our study.

Few studies at a broad geographical scale have characterized intraspecific variation in morphology of woodland hawks in the genus Accipiter. From 1999 to 2007 we investigated morphological variation in large samples of live Cooper's Hawks (A. cooperii) nesting in four study areas: coniferous woodland around Victoria, British Columbia, Canada, isolated deciduous woodlands in short-grass prairies of northwestern North Dakota, towns and rural deciduous woodlands along the border of North Dakota and Minnesota, and urban and rural mixed deciduous and coniferous landscapes of Wisconsin. These sites span 2660 km across the northern part of the species' breeding range. We measured body mass (i.e., size), wing chord, tail length, tarsus diameter, hallux length, and culmen length of breeding adults, finding significant and clinal variation in body mass (or size). The smallest and most similar-sized birds occurred in British Columbia and western North Dakota, larger birds along the border between North Dakota and Minnesota, and the largest birds in Wisconsin. Several other characters varied significantly when mass was used as a covariate. Variation by study site in mean indices of sexual size dimorphism was negligible and not significant. We speculate that the morphological differences we found, in part, are the result of geographic isolation, where diets, migratory behavior, and structural characteristics of nesting habitats vary across landscape types.

We monitored one female hack-released Osprey (Pandion haliaetus) across her lifespan and identified her migration routes over a 4-year period (2002-2006) using satellite radiotelemetry. We documented the recruitment of this bird into the breeding population and her lifetime reproductive success. This Osprey was raised at Big Muskego Lake in southeast Wisconsin, wintered at Lake Bayano in Panama (3,877 km south-southeast [163 degrees] of Big Muskego Lake), and nested near St. Paul, Minnesota (4,183 km north-northwest [343 degrees] of Lake Bayano and 446 km northwest [300 degrees] of Big Muskego Lake). The lifespan of this female was 5 years, 5 months, and her lifetime reproductive success was three young over a period of 3 years, 2005-2007, as a breeder. Migration routes of this individual Osprey changed over her lifespan; these changes may have been influenced by weather. Received 22 February 2008. Accepted 17 June 2008.

Trichomoniasis is a digestive tract disease caused by ingestion of the protozoan Trichomonas gallinae. This disease can be a significant source of mortality. No deaths of nestlings could be attributed to trichomoniasis in Cooper's Hawks (Accipiter cooperii) breeding in urban and rural environs in Wisconsin, North Dakota, and British Columbia. We detected T. gallinae in four (5.2%) of 77 nestling Cooper's Hawks during 2006 and 2007 among 42 urban nests on new study areas in southeast Wisconsin and eastern North Dakota/western Minnesota. All four infected young fledged. We did not detect T. gallinae in 52 breeding adult Cooper's Hawks on two urban study sites, nor in 28 migrant hatching year (it = 24) and adult (n = 4) Cooper's Hawks at Hawk Ridge Bird Observatory, Duluth, Minnesota in 2006-2007. Overall, we detected T. gallinae in only 2.5% of 157 Cooper's Hawks in northcentral North America. These results suggest a low prevalence of T. gallinae in Cooper's Hawks in the northern part of this hawk's breeding range.

ABSTRACT Urban landscapes vary greatly across North America and long‐term data on the nesting biology of Cooper's hawks (Accipiter cooperii) from a variety of urban environments will improve our understanding of these poorly studied populations. We studied Cooper's hawks nesting in the metropolitan Milwaukee area, Wisconsin, USA, over a 12‐year period, 1993–2004. Nesting success for 254 first nesting attempts averaged 64.6% with means of 2.27 young per laying pair and 3.53 young per successful pair. For 8 second nesting attempts (i.e., re‐nests), nesting success averaged 87.5% with means of 2.57 young per laying pair and 3.00 young per successful pair. Productivity for first nesting attempts did not vary over the 12‐year period, and productivity for re‐nests did not differ from first nesting attempts. We documented evidence of nest predation by raccoons (Procyon lotor) and red‐tailed hawks (Buteo jamaicensis). On average, second year (SY [i.e., 1‐yr‐old]) Cooper's hawks comprised 14.6% (43 of 295 breeding birds; 21.5% [37 of 172] of F and 4.9% [6 of 123] of M) of the known breeding population. The percentage of SY breeders within this population declined over the 12‐year period, suggesting a relatively young population. Cooper's hawks consistently reoccupied nest sites annually after initial discovery over an estimated 2 generations of breeding adults, suggesting that population density for our study was at least stable. We trapped 105 breeding adults, including 5 natal dispersal birds. Based on long‐term, relatively high reproduction, repeated re‐occupancy of nest sites, and confirmed recruitment from within this population, we suggest that these nesting areas were not marginal or inferior habitats and that urban Cooper's hawks in this study area were not a sink population. We recommend no active management of this population at this time; however, additional information for nesting Cooper's hawks from other urban environs will expand our knowledge base for these populations.

Abstract We studied the reproductive success of an urban–suburban red-tailed hawk (Buteo jamaicensis) population in southeast Wisconsin, USA, over a 14-year period, and we used productivity as a measure of habitat quality. Red-tailed hawk reproductive success for our study in southeast Wisconsin, USA, is consistent with other studies across North America, averaging 80.1% nesting success and 1.36 young per laying pair. Productivity for 1994 was significantly greater than other years. Red-tailed hawk productivity, an index of habitat quality, varied with habitat composition surrounding nest sites. Wetland area was the only habitat type that was significantly greater for low-productivity sites, indicating that wetlands were not beneficial for red-tailed hawk productivity in our study area. Urban habitat characteristics (i.e., area of roads and high-density urban land) were greater for high-productivity sites, and the landscape consisted of smaller habitat patches. This indicates that urban–suburban locations provided high-quality habitat for red-tailed hawks in our study area. Higher productivity in high-density urban areas suggests that the urban red-tailed hawk may be a source, not a sink, population in the metropolitan Milwaukee area. Increased nesting on human-made structures in urban locations and enhanced reproductive success for these nests reinforce this hypothesis and suggest that red-tailed hawks are adapting to this urban environment. Resource managers and urban land-use planners can incorporate high-quality red-tailed hawk habitat characteristics into urban land-use plans, thus insuring that individuals with increased fitness persist in this urban landscape.

We described urban/suburban Red-tailed Hawk (Buteojamaicensis) nesting habitat and compared nesting habitat to unused habitat based on presence and absence of Red-tailed Hawks. We developed a landscape-scale logistic model of nesting habitat occupancy, then applied it to other locations to determine whether unoccupied patches of Red-tailed Hawk nesting habitat existed in urban locations. Redtailed Hawk nesting habitat in urban/suburban Milwaukee usually included large areas of grassland and other herbaceous cover types. Urban/suburban Red-tailed Hawk nesting habitat was comprised of more than three times as much grasslands and woodlands, and had greater land-cover diversity and patch richness than unused habitat. Characteristics of unused habitat indicated that Red-tailed Hawks avoided areas of heaviest urbanization, perhaps because of insufficient hunting habitat. The logistic regression model developed from our data demonstrated that suitable, unoccupied nesting habitat existed in this urban area. As the Red-tailed Hawk population expanded into urban locations in this study area, the birds apparently were adjusting well to urbanization. Additional studies of urban raptor populations may provide valuable insight into future management considerations for wildlife in human-influenced landscapes.

Nesting Red-tailed Hawks (Buteo jamaicensis) are becoming increasingly common in urban environments. We described Red-tailed Hawk nesting habitat and reproductive success and compared urban, suburban, and rural nesting locations in southeast Wisconsin. Nest sites were classified as urban, suburban or rural if greater than or equal to 70%, 30-70%, or less than or equal to 30% of the area (706.9 ha, 1.5-km radius) around nests was used for industrial or residential purposes, respectively. Mean success and productivity of breeding Red-tailed Hawks in the metropolitan Milwaukee area from 1989-94 (N = 426) was 81.9% (range = 75.3-92.7%) and 1.43 young/breeding pair (range = 1.13-1.91), respectively. Brood size averaged 1.75 young/successful nest (range = 1.61-2.06). Productivity was variable and was significantly higher in 1994 than each of the preceding yr (P < 0.001). Based on internest distances, the density of the Red-tailed Hawk nesting population for rural locations was greater than in suburban areas and lowest in urban locations. The amount of natural microhabitat cover around nests (19.6 ha, 0.25-km radius) did not differ for urban, suburban, or rural nest sites (P = 0.967) indicating that cover was an important component of the nesting habitat of Red-tailed Hawks. Natural cover comprised about 16% of the landscape area of urban sites and 40% of this area was wooded with the remaining 60% consisting of herbaceous cover. Urban planning should consider the amount of natural cover to allow Red-tailed Hawks and other wildlife to coexist with humans in an urban environment.