William E. Stout

Serologic Evidence of West Nile Virus Infection in Three Wild Raptor Populations

Abstract We assayed for West Nile virus (WNV) antibodies to determine the presence and prevalence of WNV infection in three raptor populations in southeast Wisconsin during 2003–04. This study was conducted in the framework of ongoing population studies that started before WNV was introduced to the study area. For 354 samples, 88% of 42 adult Coopers hawks (Accipiter cooperii), 2.1% of 96 nestling Coopers hawks, 9.2% of 141 nestling red-tailed hawks (Buteo jamaicensis), and 12% of 73 nestling great horned owls (Bubo virginianus) tested positive for WNV antibodies by the constant virus–serum dilution neutralization test. Samples that tested positive for WNV antibodies were collected across a wide variety of habitat types, including urban habitats (both high and low density), roads, parking areas, recreational areas, croplands, pastures, grasslands, woodlands, and wetlands. Based on the increased prevalence and significantly higher WNV antibody titers in adults compared with nestlings, we suggest that nestlings with detectable antibody levels acquired these antibodies through passive transmission from the mother during egg production. Low levels of WNV antibodies in nestlings could serve as a surrogate marker of exposure in adult raptor populations. Based on breeding population densities and reproductive success over the past 15 yr, we found no apparent adverse effects of WNV infections on these wild raptor populations.

Nesting Biology of Urban Cooper's Hawks in Milwaukee, Wisconsin

Abstract Urban landscapes vary greatly across North America and long-term data on the nesting biology of Coopers hawks (Accipiter cooperii) from a variety of urban environments will improve our understanding of these poorly studied populations. We studied Coopers 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]) Coopers 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. Coopers 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 Coopers 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 Coopers hawks from other urban environs will expand our knowledge base for these populations.

Colonization, Growth, and Density of a Pioneer Cooper's Hawk Population in a Large Metropolitan Environment

Abstract Coopers 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 km2 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 Coopers Hawk population and its subsequent growth from 1993–2008 (4 to 41 laying pairs, 4 to 55 occupied sites). Nearest-nest distances decreased and the number of Coopers 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 Coopers Hawks in some localized areas averaged one laying pair per 330 ha (range: 68–587 ha). From 1996–2008, as breeding density increased, average annual productivity (number of young/laying pair) for Coopers 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.

Landscape Correlates of Reproductive Success for an Urban-Suburban Red-Tailed Hawk Population

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.

LANDSCAPE FEATURES OF RED-TAILED HAWK NESTING HABITAT IN AN URBAN/SUBURBAN ENVIRONMENT

ABSTRACT We described urban/suburban Red-tailed Hawk (Buteo jamaicensis) 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. Red-tailed 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.

Migration Routes, Reproduction, and Lifespan of a Translocated Osprey

Abstract 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°] of Big Muskego Lake), and nested near St. Paul, Minnesota (4,183 km north-northwest [343°] of Lake Bayano and 446 km northwest [300°] 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.

Low Prevalence of Trichomonas gallinae in Urban and Migratory Cooper's Hawks in Northcentral North America

Abstract 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 Coopers 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 Coopers 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 Coopers Hawks on two urban study sites, nor in 28 migrant hatching year (n  =  24) and adult (n  =  4) Coopers Hawks at Hawk Ridge Nature Reserve, Duluth, Minnesota in 2006–2007. Overall, we detected T. gallinae in only 2.5% of 157 Coopers Hawks in northcentral North America. These results suggest a low prevalence of T. gallinae in Coopers Hawks in the northern part of this hawks breeding range.

Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

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 Coopers 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 Coopers hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Coopers hawks in Wisconsin.

First Documented Eight-egg Clutch for Cooper's Hawks

Various indices of reproduction including clutch size, brood size, number of young recruited into the breeding population, and other reproductive parameters provide valuable information regarding survivorship, mortality, and age structure of avian populations (Newton 1998, Rosenfield et al. 2007). Here I document the first known eight-egg clutch for Cooper’s Hawks (Accipiter cooperii). This clutch was found during an ongoing investigation of urban nesting Cooper’s Hawks in Milwaukee, Wisconsin U.S.A. (43u109N, 88u009W). On 4 May 2008, I first observed an adult female Cooper’s Hawk in an incubating posture on her nest. She was observed incubating again on 30 May and 19 June with no evidence of young in the nest (i.e., excreta below nest). On 3 July, a date well past the expected hatch date given the estimated 34-d incubation period for the species, I suspected that the nest had failed because no adult was present. I climbed to the nest and found that it contained eight Cooper’s Hawk eggs (Fig. 1). I removed the eggs on 12 July and analyzed their contents. At least six of the eight eggs contained embryos in early (ca. 10–25 mm in length) to mid-developmental stages. This failed nesting attempt was located in a white pine (Pinus strobus) on residential property ca. 9–10 ha in size, which included one large community residence and several outbuildings. Mediumand high-density human residential areas, as well as industrial and commercial land surrounded this property. In 2007, five young fledged from this nest, which also contained one unhatched egg. Previously reported clutch sizes for Cooper’s Hawks ranged from 1–7 eggs per clutch (mean clutch size: 3.3– 4.3 eggs) and productivity averaged 1.6–2.8 young per laying pair (2.7–3.5 young/successful pair; Peck and James 1983, Curtis et al. 2006). Egg-laying for this species usually occurs at 2-d intervals (occasionally 3-d intervals), and incubation typically begins after the third egg is laid, but occasionally with subsequent eggs (Curtis et al. 2006). Congeneric species Sharp-shinned Hawks (A. striatus) and Eurasian Sparrowhawks (A. nisus) have both produced eightegg clutches (Bildstein and Meyer 2000, Newton 1986). Some raptors in urban landscapes tend to have higher reproductive rates than those in rural locations (Rosenfield et al. 1996, Boal and Mannan 1999, Curtis et al. 2006). Productivity of Cooper’s Hawks in the metropolitan Milwaukee area (1993–2008) was among the highest reported for this species (e.g., 3.5 young/successful pair) with seven broods of six young from 2001–2008 (Stout et al. 2006, 2007; W. Stout unpubl. data). Although the nest with eight eggs failed, reproductive parameters for the metropolitan Milwaukee area in 2008 (80% nest success, 2.6 young/laying pair, 3.2 young/successful pair, N 5 41) were comparable to other years of this study (Stout et al. 2006, 2007; W. Stout unpubl. data). Several studies also documented higher reproductive rates for a variety of other raptor species in urban environments compared to rural locations (e.g., Bloom and McCrary 1996: Red-shouldered Hawk [Buteo lineatus], Parker 1996: Mississippi Kite [Ictinia mississippiensis], Gehlbach 1996: Eastern Screech-Owl [Megascops asio]). One or more factors may have influenced this nesting failure. During the incubation period, in addition to .3.5 cm of rainfall on 30 May, record rainfall totals were set from 1–13 June for Milwaukee, Wisconsin, (.26 cm) resulting in notable flooding (U.S. Department of Commerce 2007). These extreme rainfall totals may have prevented the incubating female from keeping some, or per-