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Wednesday, 18 February 2015

Journal of Raptor Research. March 2015: Volume 49, Issue 1

Journal of Raptor Research

Published by: The Raptor Research Foundation

Table of Contents

March 2015 : Volume 49, Issue 1 

Northward Summer Migration of Red-Tailed Hawks Fledged from Southern Latitudes Full Access

Peter H. Bloom, Michael D. McCrary, J. Michael Scott, Joseph M. Papp, Karyn J. Sernka, Scott E. Thomas, Jeff W. Kidd, Edmund H. Henckel, Judith L. Henckel, and Marjorie J. Gibson
pg(s) 1–17
With a breeding range extending from approximately 68°N in northern Canada to 8°N in Panama, Red-tailed Hawks (Buteo jamaicensis) exhibit migrations that vary substantially with latitude. Northern populations are almost completely migratory, middle-latitude populations are partially migratory, and southern populations south of 38°N are considered sedentary. Contrary to the latter widely held belief, we found that many juveniles and young adults from one population below 38°N are also partially migratory. However, unlike most birds in the northern hemisphere that migrate south in autumn, young Red-tailed Hawks from our southwestern California study area migrated north in summer to summering areas as far as 1462 km from their natal nests. Of the 5271 Red-tailed Hawk nestlings we banded in the study area and an additional 189 banded by other researchers, 205 were encountered (found dead or alive or recaptured) outside the study area. We classified 64 encountered hawks as potential migrants, most (69%) of which were encountered to the north of their natal nest (median  =  383 km). We found that juveniles and young adults banded south of 35°N in the Pacific Flyway migrated north, whereas those banded north of 40°N migrated south. Sixteen hawks from the study area equipped with satellite transmitters as fledglings migrated north (range 342–24°) in summer, up to 1388 km, and returned to their natal region in autumn of the same year. This pattern was repeated annually until they acquired a mate and territory. Our results showed that many or most young Red-tailed Hawks migrate northward in the summer, and we propose that this pattern may be a response to historical climate changes, seasonal changes in sciurid prey availability, and/or dominance of territorial adults.

Nest Guarding in Chesapeake Bay Bald Eagles Full Access

Courtney Turrin and Bryan D. Watts
pg(s) 18–28
As Bald Eagle (Haliaeetus leucocephalus) populations approach carrying capacity in the Chesapeake Bay, competition for breeding territories appears to be intensifying. Frequent territorial interactions may force breeders to adjust nest-guarding behavior. We examined nest-guarding behaviors at active Bald Eagle nests in the lower Chesapeake Bay during the nesting season (2012 and 2013). Guarding coverage was 13.7 ± 4.2% of total observation time during the pre-laying period, 6.8 ± 2.2% of observation time in the incubation period, and 26.3 ± 3.2% of observation time in the nestling period. Females were present in the nest area for 80.0 ± 2.7% of the nestling period. Although males were present only 51.2 ± 2.8% of the nestling period, male breeders guarded nests twice as often as females. Adults guarded most often from perches in adjacent trees and within 25 m of the nest. If increasing rates of conspecific interactions force males to allocate more time to nest guarding, a tradeoff may occur, with males dividing time between guarding the nest and foraging for food to provision offspring.

Daytime Habitat Selection by Resident Golden Eagles (Aquila chrysaetos) in Southern Idaho, U.S.A Full Access

Chad W. LeBeau, Ryan M. Nielson, Eric C. Hallingstad, and David P.Young, Jr.
pg(s) 29–42
Energy and other anthropogenic development are increasing throughout the range of Golden Eagles (Aquila chrysaetos) in western North America, and both private and government agencies have expressed concern about indirect and direct effects on Golden Eagles. To facilitate sustainable development and reduce risk to Golden Eagles, the U.S. Fish and Wildlife Service has established guidelines to assist developers in project planning and siting. A major component of environmental impact assessment is documenting Golden Eagle spatial use near a project site before development. Unbiased estimates of habitat selection (spatial use) in and near a proposed project area are possible with location data collected by Global Positioning System (GPS) transmitters attached to a sample of Golden Eagles in the area. During spring 2011, we identified occupied Golden Eagle territories within a study area in southern Idaho, and deployed four GPS and Argos tags on resident adult Golden Eagles. We developed seasonal resource selection functions (RSFs) for each monitored Golden Eagle, and estimated seasonal daytime habitat selection by the average Golden Eagle by averaging predictions from four RSFs. The final RSFs estimated that relative probability of selection by Golden Eagles was highest closer to nests and over moderately rugged terrain. Other predictor variables such as brightness (a measure of non-vegetated habitats) and slope were also seasonally important. Model validation indicated the models reliably predicted Golden Eagle use within the study area. This is the first study estimating Golden Eagle habitat selection based on a combination of GPS and nest locations. The process we developed may be used to improve our understanding of Golden Eagle habitat selection and to provide valuable information to help minimize risk to Golden Eagles from different land management practices.

Using Feathers to Determine Mercury Contamination in Peregrine Falcons and Their Prey Full Access

Joseph G. Barnes, Shawn L. Gerstenberger
pg(s) 43–58
We document concentrations of total mercury (Hg) in feathers of Peregrine Falcons (Falco peregrinus) from 12 territories in Lake Mead National Recreation Area (LMNRA) and five territories in an adjacent southern Nevada (SNV) study area during 2012 and 2013. We also report total Hg concentrations in feathers of 94 species (337 individuals) collected as prey remains from peregrine nesting areas from 2008–2013. All peregrine feathers contained total Hg (range  =  0.12–42.54 µg/g), and adults had a significantly higher mean total Hg concentration (12.19 µg/g) than hatch-year peregrines (3.76 µg/g). Mean total Hg concentrations in peregrines in LMNRA (adult  =  17.24 µg/g, brood  =  5.82 µg/g) were significantly greater than in SNV (adult  =  2.7 µg/g, brood  =  0.67 µg/g) for both age classes. Among peregrine territories, mean total Hg in prey was positively correlated with the proportion of aquatic birds taken as prey (biomass), and negatively correlated with distance of eyries to water. Among avian prey, the mean total Hg concentration in aquatic birds (5.07 µg/g) was significantly higher than terrestrial birds (0.76 µg/g), and aquatic invertivores were the most contaminated foraging guild (mean  =  6.17 µg/g). Eared Grebes (Podiceps nigricollis) were the prey species with the highest mean total Hg concentration (12.27 µg/g). Peregrine Falcons, with their broad distribution, catholic diet, and use of diverse habitat types, may be an ideal indicator species of environmental Hg contamination. Contaminant studies incorporating prey analysis are useful to assess exposure pathways and evaluate potential ecological effects across a broad array of habitat types.

The Rusty Plumage Coloration of Juvenile Gyrfalcons is Produced by Pheomelanin and its Expression is Affected by an Intracellular Antioxidant Full Access

Ismael Galván, Alberto Jorge
pg(s) 59–65

Juveniles of many diurnal raptors exhibit a characteristic rusty plumage coloration whose biochemical basis has never been determined. Using the Gyrfalcon (Falco rusticolus) as a model species, we analyzed feathers by Raman spectroscopy and showed that the rusty color is due to the presence of the pigment pheomelanin, which was also observed in the feathers of a juvenile Peregrine Falcon (Falco peregrinus). We experimentally modified the expression of the rusty plumage coloration by treating four developing Gyrfalcons with buthionine sulfoximine (BSO), a specific and nontoxic inhibitor of glutathione (GSH) synthesis. Because cysteine, one of the three constitutive amino acids of GSH, is required for pheomelanin synthesis and GSH is the most important intracellular antioxidant, these findings indicate that the expression of rusty plumage coloration can be affected by environmental oxidative stress. Our results suggest that the rusty plumage coloration of at least some diurnal raptors is pheomelanin-based, and the dependence on GSH levels opens the possibility that the evolution of this trait in some species and the age-related variation in its expression across species may be explained by interspecific and intraspecific variation in exposure to environmental factors that generate oxidative stress and by age-related variations in endogenous levels of oxidative stress.

When Owls go to Town: the Diet of Urban Barred Owls Full Access

Sofi Hindmarch and John E. Elliott
pg(s) 66–74
We investigated the diet of Barred Owls (Strix varia) inhabiting urban environments in the Lower Fraser Valley of southwestern British Columbia, Canada. Our objective was to use the diet information to gain insight into the pathways of exposure to anticoagulant rodenticides (ARs) previously documented in this owl species. In particular, we examined whether such exposure is driven by the consumption of rodents commonly targeted during AR application, Norway rats (Rattus norvegicus), black rats (Rattus rattus) and house mice (Mus musculus), or if the secondary exposure is via consumption of native non-target rodents feeding at outdoor bait-stations. We identified 688 prey items from eight urban nest/roost sites. Rats (54.5%) were by far the most common prey, followed by field voles (Microtus townsendii; 19.3%), and deer mice (Peromyscus maniculatus; 5.2%). The consumption of rats was positively correlated with the degree of urban development within Barred Owl home ranges (rp  =  0.70, r2  =  0.48, P < 0.05, one-tailed). Barred Owls consumed predominantly younger rats, as the average rat weight was 103 ± 51.7 grams (n  =  164). Surprisingly, no house mice were found in the prey remains, supporting the assumption that house mice seldom venture outdoors and therefore are not a likely vector of ARs to owls. If we assume more intensive AR usage in urban environments, then the higher consumption of rats in urban areas implicates rats as the likely pathway for secondary AR exposure to Barred Owls in urban landscapes.

Distributional Changes in the Western Burrowing Owl (Athene cunicularia hypugaea) in North America from 1967 to 2008 Full Access

Alberto Macías-Duarte, Courtney J. Conway
pg(s) 75–83
The quantification of shifts in bird distributions in response to climate change provides an opportunity to gain a deeper understanding of the processes that influence species persistence. We used data from the North American Breeding Bird Survey (BBS) to document changes in the distributional limits of the western Burrowing Owl (Athene cunicularia hypugaea) from 1967 to 2008. We used logistic regression to model presence probability (p) as a function of longitude, latitude, and year. We modeled a linear trend in logit(p) through time with slope and intercept modeled as a double Fourier series of longitude and latitude. We found that the western Burrowing Owl has experienced an intriguing southward shift in the northern half of its breeding range, contrary to what is predicted by most species niche models and what has been observed for many other species in North America. The breeding range of the Burrowing Owl has been shrinking near its northern, western, and eastern edges. Our model detected the population declines that were observed in California and eastern Washington, in locations where maps based on route-specific estimating equations had predicted significant population increases. We suggest that the northern boundary of the breeding distribution of the western Burrowing Owl has contracted southward and the southern boundary of the species' breeding distribution has expanded southward into areas of northern Mexico that were formerly used only by wintering migrants.


Plumage Aberrations in Northern Saw-whet Owls (Aegolius acadicus) Full Access

Scott Weidensaul, Marten Stoffel, Mark S. Monroe, David Okines, Bill Lane, John Gregoire, and Sue Gregoire, Tim Kita
pg(s) 84–88
Describe two chromatic aberrations plumage not previously documented in individuals of Northern saw-whet owl caught for ringing in the United States and Canada, between 2007 and 2012. Eight individuals exhibited a "cake dilution" with a reduced intensity of black and brown pigments, consistent with -50% reduction in the levels of eumelanin and pheomelanin. Individuals A. acadicus presented beak and claws pale but normally pigmented and pigmented iris. Four of the eight individuals captured were classified as based on wing moult (two individuals of two years and two individuals over two years) adults, suggesting that the aberration is not an impediment to survival. We also describe an individual of A. acadicusless than one year old partial leucismo, which were absent wide colored ferruginous and vertical bars normally found in the chest and upper chest.Both aberrations appear to be extremely rare, occurring only eight times and once, respectively, from> 30 000 individuals captured for banding.

Increasing Capture Frequency for Flammulated Owls and Northern Saw-whet Owls During Fall Migration Full Access

Jessica Pollock, Jay D. Carlisle, Chad Runco, and Gregory Kaltenecker
pg(s) 88–92
We have been banding individuals Psiloscops flammeolus and Northern saw-whet owl during the fall migration in Idaho since 1998. Our mist nets hearing lures are located within forests Pseudotsuga menziesii with very little undergrowth. During the fall of 2011 we observed some individuals ofP. flammeolus within dense patches of deciduous shrubs mountain located up to 100 m away from the ear lure. Therefore, half of the 2011 season, experimentally mist nets placed within these dense deciduous shrub habitats to assess if we could increase the frequency of capture P. flammeolus, which is listed as a species of concern by most state and federal agencies within its breeding. Standardize the protocol for the seasons of 2012 and 2013. The mist nets were placed in dense thickets catch rates of P. flammeolus of 7-21 times higher than our traditional mist nets placed in the understory, suggesting that the site of networks in this habitat may be valuable for studies of annealing. Although our primary goal was to increase the catch rate of individuals of P. flammeolus also documented a smaller increase in the rate of capture of A. acadicus in the same networks.

Trapping Success Using Carrion with Bow Nets to Capture Adult Golden Eagles in Sweden Full Access

Peter H. Bloom, Jeff W. Kidd, and Scott E. Thomas, Tim Hipkiss and Birger Hörnfeldt, Michael J. Kuehn
pg(s) 92–97
There are numerous methods and devices available to catch prey species of large, but the relative effectiveness of these methodologies is poorly documented in the literature. As part of several proposals to develop wind power projects in northern Sweden, we tried to capture adults of Aquila chrysaetos within their breeding grounds to place them transmitters. Our attempts to capture took place in late autumn and early winter in northern Sweden, where individuals of A. chrysaetos often eat offal left by hunters and corpses product of collisions with vehicles. Due to restrictions in Scandinavia regarding the use of live animals as bait, traps selection was limited to those types of traps that work successfully with carrion. For this reason, we use networks arc based on the existence of previous successful experiences with carrion, ease of transport and quick to assembly. Normally we operate two to three traps in 2010 and three to four traps in 2011, totaling 120 trap-days (54 in 2010 and 66 in 2011) in hiding for a total of 993 hours (400 in 2010 and 593 in 2011). We captured 30 (8 in 2010 and 22 in 2011) adult individuals of A. chrysaetos in 16 territories. The highest catch rate occurred in September, prior to the dispersal of young people and adults before some disperse from their breeding grounds.

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