Cheryl R. Dykstra

NEST SITE SELECTION AND PRODUCTIVITY OF SUBURBAN RED-SHOULDERED HAWKS IN SOUTHERN OHIO

Abstract We measured nest site selection and productivity of suburban-nesting Red-shouldered Hawks (Buteo lineatus) in southwestern Ohio and rural-nesting Red-shouldered Hawks in south-central Ohio. At both the suburban and the rural locations, nest sites had greater canopy height and overall tree basal area than paired random plots, and were located closer to water than were paired random plots. Nest trees also had greater diameter and height than random plot-center trees. Reproductive rates at suburban and rural sites were similar, averaging 2.6–3.1 nestlings per successful nest. Results indicated that suburban-nesting Red-shouldered Hawks were very similar to rural-nesting hawks in both nest site selection and productivity, suggesting that Red-shouldered Hawks were habituated to their suburban environs.

HOME RANGE AND HABITAT USE OF SUBURBAN RED-SHOULDERED HAWKS IN SOUTHWESTERN OHIO

Abstract We measured the home ranges and habitat use of 11 Red-shouldered Hawks (Buteo lineatus) during the breeding season and 9 during the nonbreeding season in suburban Ohio, using standard telemetry techniques. Mean home ranges, calculated using the adaptive kernel method (95% isopleth), were 90 ha ;pm 11 SE during the breeding season, 189 ha ;pm 33 SE during the nonbreeding season, and 165 ha ;pm 24 SE for the annual home range. Males and females did not differ significantly in home range size. We examined habitat use by hawks by classifying the habitat where birds were observed perching. Habitat used by hawks differed significantly from that available within home ranges for all birds tested. Most Red-shouldered Hawks used riparian zones and pond edges more than expected, based on availability of such habitats within their home ranges; residential areas and lawns were used less than expected or in proportion to their availability.

CORRELATION OF RED-SHOULDERED HAWK ABUNDANCE AND MACROHABITAT CHARACTERISTICS IN SOUTHERN OHIO

Abstract We measured an index of Red-shouldered Hawk (Buteo lineatus) abundance along streams in southern Ohio and related differences in abundance index to landscape-scale habitat characteristics within the surveyed areas. Fifteen study sites, each a 5.8-km reach of a permanent stream, were surveyed four times using broadcasts of Red-shouldered Hawk calls and Red-tailed Hawk (Buteo jamaicensis) calls. We determined the landcover types in a corridor surrounding each surveyed area using a GIS landcover data grid, and counted the number of small ponds within each corridor. We calculated hawk response rate for each species as the mean number of visual or aural detections per survey. Red-shouldered Hawk response rate was inversely correlated to Red-tailed Hawk response rate (r = −0.52, P < 0.04), and was positively correlated to the number of small ponds within each stream corridor (r = 0.77, P < 0.01), suggesting that the number of small ponds was an important factor associated with Red-shouldered Hawk abundance. Correlación entre la Abundancia de Buteo lineatus y Características de Macrohábitat en el Sur de Ohio Resumen. Calculamos un índice de abundancia de Buteo lineatus a lo largo de varios arroyos en el sur de Ohio y relacionamos las diferencias en este índice con características del hábitat a escala del paisaje de las áreas censadas. Trabajamos en 15 sitios (cada uno comprendiendo 5.8 km alrededor de un arroyo permanente), que fueron censados cuatro veces reproduciendo vocalizaciones de B. lineatus y B. jamaicensis. Determinamos el tipo de uso de la tierra en un corredor alrededor de cada área censada utilizando un sistema de información geográfica y contamos el número de pequeños estanques al interior de cada corredor. Calculamos la tasa de respuesta de las dos especies de gavilanes como el número promedio de detecciones visuales o auditivas por censo. La tasa de respuesta de B. lineatus se correlacionó negativamente con la tasa de respuesta de B. jamaicensis (r = −0.52, P < 0.04) y positivamente con el número de estanques dentro de cada corredor (r = 0.77, P < 0.01). Los resultados sugieren que el número de estanques es un factor importante asociado a la abundancia de B. lineatus.

Habitats of Suburban Barred Owls (Strix varia) and Red-Shouldered Hawks (Buteo lineatus) in Southwestern Ohio1

Abstract Little is known about the habitat and ecology of suburban Barred Owls (Strix varia), a species sometimes considered the nocturnal equivalent of Red-shouldered Hawks (Buteo lineatus). We compared nesting habitat of Barred Owls to that of Red-shouldered Hawks nesting in suburban and urban areas, in and near the city of Cincinnati, Ohio, to determine whether any features distinguished owl nest sites from hawk nest sites. We characterized habitat and land-cover metrics in circular plots of 100 ha and 15 ha, centered on the owl and hawk nests, using ATtiILa software operating within a GIS environment. For the 100-ha plots, the primary cover type in the plots surrounding nests of both species was forest, 41.4 ± 3.4% for Barred Owl plots and 45.9 ± 3.4% for Red-shouldered Hawk plots, followed by low-density residential land: 29.8 ± 4.8% of the Barred Owl plots and 29.3 ± 3.7% of the Red-shouldered Hawk plots. Pasture composed <15% of the plot area for both species and the remainder of the cover types contributed even less. Values of land-cover percentages and metrics did not differ between the species (P > 0.05), for either the large plots or the small (15-ha) plots. Using stepwise binary logit regression analysis, we found that no variables discriminated owl plots from hawk plots. We concluded, based on our methodology, that habitat of suburban Barred Owls differed little from habitat of suburban Red-shouldered Hawks in southwestern Ohio.

Patterns and trends in brominated flame retardants in bald eagle nestlings from the upper midwestern United States.

We report on patterns and trends in polybrominated diphenyl ethers (PBDEs) in the plasma of 284 bald eagle nestlings sampled between 1995 and 2011 at six study areas in the upper Midwestern United States. Geometric mean concentrations of total PBDEs (Σ of nine congeners) ranged from 1.78 ng/mL in the upper St. Croix River watershed to 12.0 ng/mL on the Mississippi River. Lake Superior nestlings fell between these two extremes. Between 2006 and 2011, trends differed among study areas with three declining, two remaining stable, and one increasing. Variation in ΣPBDE trends among study areas was linked to trends in individual congeners. The lower brominated PBDEs (BDE-47, -99, and -100) declined 4-10% while the higher brominated congeners (BDE-153 and -154) increased by about 7.0% annually from 2006 to 2011. This increase was the greatest in nestlings from the St. Croix River and below its confluence with the Mississippi River. Region-wide, our data suggest ΣPBDEs increased in bald eagle nestlings from 1995 through the mid-2000s and then declined by 5.5% annually from 2006 to 2011. These regional trends are consistent with the removal of penta- and octa-PBDEs from the global market.

Causes of Mortality and Failure at Suburban Red-Shouldered Hawk (Buteo lineatus) Nests1

Abstract There have been no detailed studies of predator or non-predator causes of mortality and failure at nests of the Red-shouldered Hawk (Buteo lineatus), and identification of such causes has been largely speculative. There is ample information about rates of nest success, defined as the fledging of ≥1 nestling from a nest, but this measure of reproductive rate is limited in its scope. Fledging success, measured by quantifying total nestlings lost or fledged is a more informative assessment of reproductive success, but is not often reported. We used video monitoring of suburban Red-shouldered Hawk nests to identify causes of mortality or failure. Eight of 25 nests failed completely (32%), and 17 were successful (68%). However, nine of the 17 successful nests experienced some nestling mortality, and the fledging success of individual nestlings (n  =  67) was only 58%, as 28 nestlings (42%) died before fledging. Causes of mortality or nest failure included depredation of an incubating female parent at one nest and of nestlings at multiple nests by Great Horned Owls (Bubo virginianus), depredation of nestlings by raccoons (Procyon lotor), disturbance by eastern gray squirrels (Sciurus carolinensis), unexplained disappearance of female parents, starvation of nestlings, and nestlings falling from the nest. These results provide a thorough and accurate account of reproductive success, and valuable identification of predator and non-predator causes of nestling mortality or nest failure throughout the nesting period.

Selection of Fresh Vegetation for Nest Lining by Red-shouldered Hawks

Abstract Red-shouldered Hawks (Buteo lineatus) typically line their nests with fresh branches of coniferous and deciduous trees. We recorded all species of green material present in 63 nests from 2003 to 2005 in suburban Cincinnati in southwestern Ohio, and in 35 nests in Hocking Hills in southeastern Ohio, United States. We identified all trees within 0.08-ha plots at 33 nest sites in southwestern Ohio and 30 in Hocking Hills. Red-shouldered Hawks in southwestern Ohio and Hocking Hills used black cherry (Prunus serotina) branches as a nest lining more frequently than expected, based on Baileys 95% confidence intervals. Black cherry was found in >80% of nests but present in only 57–58% of the vegetation plots, and composed only 4–5% of the trees in the forests of the study areas. White pine (Pinus strobus), red pine (P. resinosa), and eastern hemlock (Tsuga canadensis) also were used more than expected in both study areas. Black cherry is a cyanogenic species and may provide an advantage to nesting Red-shouldered Hawks by functioning as a natural pesticide.

Sexing Adult and Nestling Red-Shouldered Hawks Using Morphometrics and Molecular Techniques1

Abstract Sexing of raptors is important for understanding their ecology and demography. Males and females of monomorphic species such as Red-shouldered Hawks (Buteo lineatus) may be distinguished using molecular and morphometric techniques. We collected blood samples and morphometric measurements from adult and nestling Red-shouldered Hawks in southern Ohio. We determined sex via amplification of the sex-linked chromo-helicase-DNA-binding gene and polymerase chain reaction. We used a suite of morphometric measurements to generate a recursive partitioning classification tree and in a linear discriminant analysis to determine the sex of adults and nestlings. For adults, the recursive partitioning tree utilized only mass to distinguish sexes, with an overall successful classification rate of 94%. For nestling hawks aged approximately 3 wk and older, mass and toepad (footpad) length were used to distinguish the sexes, with an overall successful classification rate of 91%. The ability to sex adults and nestlings in the field is valuable for studies of dispersal, survival, and behavior.

DAILY ENERGY EXPENDITURE OF NESTLING BALD EAGLES IN NORTHERN WISCONSIN

Abstract We measured field metabolic rate of nestling Bald Eagles (Haliaeetus leucocephalus) in northern Wisconsin, using doubly-labeled water. In inland northern Wisconsin and along the Wisconsin Lake Superior shore, eaglets aged 39–60 days, weighing 3.08–4.85 kg, expended an average of 2,427 ± 100 kJ day−1. Nestling field metabolic rate was weakly correlated with nestling age, but not with mass. Field metabolic rate of eaglets can be used to estimate the biomass of food that adult eagles must provide from their environment, a datum that is important for determination of habitat suitability.

Protocalliphora (Diptera: Calliphoridae) Infestations of Nestling Red-shouldered Hawks in Southern Ohio

Abstract We examined nestling Red-shouldered Hawks (Buteo lineatus) in 56 nests (147 nestlings) in suburban southwestern Ohio and in 25 nests (67 nestlings) in rural forested Hocking Hills in south-central Ohio, ∼180 km east of southwestern Ohio. Fifteen of 25 nests in Hocking Hills had Protocalliphora avium larvae on one or more nestlings and/or pupae in the nest material. Nineteen nestlings had larvae in one or both ears, an additional 14 had evidence of larvae outside the ears, 32 were not visibly parasitized, and two were not examined or their status was not reported; in contrast, no nests and no nestlings were parasitized in southwestern Ohio. Reproductive rate (young fledged/nest) did not differ between southwestern Ohio and Hocking Hills (2.4 ± 0.1 young/nest at southwestern Ohio vs. 2.7 ± 0.2 at Hocking Hills; P  =  0.214). Parasitized nests at Hocking Hills were no more likely to have been used in the previous breeding season than non-parasitized nests (χ2  =  0.903, P  =  0.342, n  =  22). Similarly, number of young fledged/nest at parasitized nests did not differ from that at non-parasitized nests within Hocking Hills (U  =  75.0, P  =  1.00, n  =  25; mean (± SE) number of young  =  2.7 ± 0.3 vs. 2.7 ± 0.3 at parasitized and non-parasitized nests, respectively). The Protocalliphora loads we observed did not appear to have a negative effect on the fledging rate of nestling Red-shouldered Hawks; however, we did not assess any other potential effects of parasitism.