Search birdRS Box

Search birdRS blog posts

Browse the Blog Posts

Or scan through the blog archive below for items of interest as only the latest post is shown below, thanks.

Wednesday, 2 December 2015

Journal of Raptor Research: December 2015, Vol 49, Issue 4. Abstracts

Journal of Raptor Research
Published by: The Raptor Research Foundation

Dec 2015 : Volume , 49 Issue 4 


Research Articles

Long-term Reproduction (1984–2013), Nestling Diet, and Eggshell Thickness of Peregrine Falcons (Falco peregrinus) in Yellowstone National Park
Lisa M. Baril, David B. Haines, Douglas W. Smith and Robert J. Oakleaf

Peregrine Falcons (Falco peregrinus) were extirpated from Yellowstone National Park (YNP) by 1970 as a result of widespread use of DDT (dichloro-diphenyl-trichloroethane) throughout North America from the late 1940s to the early 1970s. DDT, and its primary metabolite DDE (dichloro-diphenyl-dichloroethylene), caused eggshell thinning and impaired reproduction in Peregrine Falcons and other raptors. Restoration of Yellowstone’s Peregrine Falcon population began with nationwide restrictions placed on the use of DDT in 1972, coupled with the release of 36 captive-raised juveniles in YNP and the dispersal of 644 captive-raised juvenile Peregrine Falcons released within 260 km of YNP. We monitored Peregrine Falcon reestablishment and reproductive success in YNP (nesting success, productivity, and brood size) from 1984–2013. Productivity was defined as the number of young reaching ≥28 d per territorial pair. Brood size referred to the number of young reaching ≥28 d per successful pair. From 2010–2013, we collected and analyzed prey remains and eggshell fragments from nine Peregrine Falcon territories across YNP. We documented a substantial increase in the number of occupied territories from one in 1984 to 32 by 2007, as well as high nesting success (74%), productivity (1.62 young/territorial pair), and brood size (2.18 young/successful pair) during 1984–2013. Nesting success, productivity, and brood size were at or above the target values identified by U.S.F.W.S. and those found for the Rocky Mountain/Great Plains region during the 2003 national survey. Peregrine Falcon eggshells collected at the nine eyries were 4% thinner than pre-1947 measurements (pre-DDT) and presumably indicate low DDE concentrations. Prey remains were dominated by birds (97% of individuals), mostly terrestrial species (63%) including American Robins (Turdus migratorius), Franklin’s Gulls (Leucophaeus pipixcan), and Mountain Bluebirds (Sialia currucoides).

Establishment and Growth of the Peregrine Falcon Breeding Population Within the Mid-Atlantic Coastal Plain
Bryan D. Watts, Kathleen E. Clark, Craig A. Koppie, Glenn D. Therres, Mitchell A. Byrd and Karen A. Bennett

Between 1975 and 1985, 307 captive-reared Peregrine Falcons (Falco peregrinus) of mixed heritage were released within the mid-Atlantic Coastal Plain, a physiographic region with no historical breeding population, as part of the eastern peregrine recovery program. We have monitored the size, distribution, reproductive rate, and substrate use of the resulting breeding population (1979–2007). The population proceeded through an establishment phase (1979–1985) driven by releases with an average population doubling time of 1.3 yr to a consolidation phase (1986–2007) with an average doubling time of 23.4 yr. The region supported 55 breeding pairs by 2007. Reproductive rates have increased significantly over the study period from 1.18 young/occupied territory (1980–1987) to 1.87 young/occupied territory (1998–2007), and average nesting success increased from 66.3% to 79.9%. All breeding pairs nested on artificial substrates, including towers built for the peregrines (n  =  37), bridges (n  =  29), buildings (n  =  7) and an assortment of other structures. Substrate use has diversified over time, with towers making up 100% of nesting structures in the early period of establishment and only 45% by 2007. The population appears to be self-sustaining, with reproductive rates exceeding 1.5 young/occupied territory every year since 1999.

Clarifying Subspecies of Peregrine Falcons Along the Lost Coast of Alaska
Stephen B. Lewis and Michelle L. Kissling

The concept of subspecies is an important tool to help categorize and conserve biodiversity; thus, delineating the range of subspecies can have important management and conservation implications. The Peregrine Falcon (Falco peregrinus) is a widespread species that occurs throughout North America, where three subspecies are recognized: F. p. anatum, F. p. pealei, and F. p. tundrius. In Alaska, all three subspecies breed and their general distributions during the breeding season are well documented. However, the limits of their distributions were unclear or unconfirmed, especially those of F. p. anatum and F. p. pealei along the Lost Coast in the northeastern Gulf of Alaska. We describe plumage, morphology, and/or movements of Peregrine Falcons known to have nested (n  =  6) or hatched (n  =  3) within the Lost Coast and used this information to determine their subspecific group. For all nine birds, we found these characteristics to be consistent with F. p. anatum. Our results underscore the importance of delineating geographic range and distribution of subspecies prior to environmental catastrophes and to ensure reliable interpretation of species status and trends. We believe this type of life-history and demographic information will become even more valuable as the effects of a changing climate are realized.

Diet of Peregrine Falcons (Falco peregrinus) in Korea: Food Items and Seasonal Changes
Chang-Yong Choi and Hyun-Young Nam

Although the diet of Peregrine Falcons (Falco peregrinus) has been studied worldwide, little information on the species’ feeding behavior has been reported for East Asia. To document prey composition and seasonal foraging habits, we collected prey remains and observed hunting behavior of Peregrine Falcons from 2001 to 2013 in the Republic of Korea. We identified 362 prey items comprising 77 species, including two insect species, two globally threatened avian species, and three owls. We found wide variation in prey mass, ranging from 0.3 g to 1103 g; the geometric mean prey weight (GMPW) was 128.8 ± 3.5 g, and 74.3% of prey taxa were <240 g in body mass. The diversity and body mass of peregrine prey varied seasonally; peregrines tended to hunt for a few large-bodied prey species in winter when nonbreeding waterbirds were most abundant, whereas they fed on small- to medium-sized birds during other seasons. In particular, peregrines fed on more species in spring and autumn, likely because of the increased diversity and abundance of migratory birds in those seasons. Our results indicated that Peregrine Falcons in Korea show opportunistic food habits, with diet varying according to seasonal prey availability.

The Effect of Supplemental Feeding on the Known Survival of Reintroduced Aplomado Falcons: Implications for Recovery
Lily Sweikert and Mike Phillips

The northern Aplomado Falcon (Falco femoralis septentrionalis) inhabited the inland and coastal grasslands of Texas, New Mexico, and Arizona until about 1930, when records of aplomados in the United States decreased. In 1986, the species was classified as endangered under the Endangered Species Act. Among other recovery efforts, 102 birds were released from 2006 through 2011, in its former range in New Mexico at the Armendaris Ranch in the south–central portion of the state. To promote their survival, an extended supplemental feeding program was conducted. From 2006 through 2008, supplemental food was provided daily, whereas from 2009 through 2011 food was provided every other day. Providing food once daily corresponded with an increase in the known survival of the aplomados, where known survival was obtained from the recorded observations of falcons at feedings, and the establishment of nearby nesting pairs. Unfortunately, this increase in known short-term survival and reproduction did not seem to lead to long-term survival or retention. This may be attributable to a lack of available prey throughout the Chihuahuan Desert as a result of ongoing drought, significant brush encroachment caused by historic overgrazing by cattle, the eradication of prairie dogs, and decreased summer and increased winter precipitation, as well as a possible increase in predation influenced by brush encroachment and the fact that the Armendaris Ranch sits at the northernmost edge of the aplomados’ historical range. If the reintroduction on the Armendaris Ranch, and other areas with similar levels of prey, is to continue, our research supports the incorporation of an extended daily supplemental feeding program and efforts to improve access to prey, possibly by removing brush and restoring grasslands.

Nesting Pair Density and Abundance of Ferruginous Hawks (Buteo regalis) and Golden Eagles (Aquila chrysaetos) from Aerial Surveys in Wyoming
Lucretia E. Olson, Robert J. Oakleaf, John R. Squires, Zachary P. Wallace and Patricia L. Kennedy

Raptors that inhabit sagebrush steppe and grassland ecosystems in the western United States may be threatened by continued loss and modification of their habitat due to energy development, conversion to agriculture, and human encroachment. Actions to protect these species are hampered by a lack of reliable data on such basic information as population size and density. We estimated density and abundance of nesting pairs of Ferruginous Hawks (Buteo regalis) and Golden Eagles (Aquila chrysaetos) in sagebrush steppe and grassland regions of Wyoming, based on aerial line transect surveys of randomly selected townships. In 2010 and 2011, we surveyed 99 townships and located 62 occupied Ferruginous Hawk nests and 36 occupied Golden Eagle nests. We used distance sampling to estimate a nesting pair density of 94.7 km2 per pair (95% CI: 69.9–139.8 km2) for Ferruginous Hawks, and 165.9 km2 per pair (95% CI: 126.8–230.8 km2) for Golden Eagles. Our estimates were similar to or lower than those from other studies in similar locations in previous years; thus, we recommend continued monitoring to determine trends in nesting pair density over time. Additionally, we performed double-observer surveys on a subset of transects with a helicopter as the second observation aircraft. We estimated probability of detecting occupied nests from fixed-wing plane versus helicopter, as well as time and expense of each survey mode. Although observers surveying from helicopters were 1.19 and 1.12 times more likely to detect Ferruginous Hawk and Golden Eagle occupied nests, respectively, the helicopter survey was 4.55 times costlier due to longer flight time and the higher hourly costs. Thus, when systematically surveying large areas, we found cost and time of the helicopter surveys outweighed the increase in nest detection.

Habitat Selection and Factors Influencing Nest Survival of Golden Eagles in South-Central Montana
Ross H. Crandall, Bryan E. Bedrosian and Derek Craighead

Golden Eagle (Aquila chrysaetos) population trends in the western United States are unclear, but an increase in future threats is causing concern for the species. Understanding the resource requirements of Golden Eagles will be essential to the creation of an effective management approach. Yet, we currently lack sufficient information on the basic habitat requirements of Golden Eagles, which hinders creation of a successful conservation plan. We took a multiscaled approach to identify factors influencing habitat selection of breeding Golden Eagles in south-central Montana. In addition, we tested environmental factors we predicted would influence daily nest survival rates to understand environmental influences on breeding success. From the 2010–2013 nesting seasons, we located 45 nesting territories and identified 115 apparent nest initiations (defined as nests where eggs have apparently been laid). We collected 15,182 telemetry locations from 12 breeding Golden Eagles. We found that Golden Eagles selected home ranges based on the percent of intermixed shrub and grassland and terrain ruggedness. At the within-home range scale, Golden Eagles selected areas based on aspect, distance to their nest, and an interaction between proximity to prey habitat and terrain ruggedness. Despite Golden Eagle selection of rugged topography, daily nest survival was negatively influenced by topographic ruggedness. Based on our results, we suggest that to maintain breeding pairs of Golden Eagles in areas similar to our study area, management should focus on preserving adequate prey habitat in areas with rugged topography. However, territories with higher ruggedness may not be as productive; therefore, management goals should be clear and environmental factors influencing both habitat selection and reproductive success should be considered when possible.

Space Use and Habitat Selection by Adult Migrant Golden Eagles Wintering in the Western United States
Robert Domenech, Bryan E. Bedrosian, Ross H. Crandall and Vincent A. Slabe

Recently, there has been an increase in concern for Golden Eagle populations in the western United States, stemming from a marked decrease in the number of migrants and an increase in future threats from a variety of factors including, but not limited to, energy development. Part of an effective conservation strategy for Golden Eagles involves understanding basic requirements of the eagles during both the breeding and nonbreeding seasons. We used PTT and GPS/PTT transmitter data from 14 adult, migratory Golden Eagles captured near the Rocky Mountain Front in Montana to determine the location and size of winter ranges and habitat use and selection within chosen winter ranges. We found large variability in location and size of winter ranges in the western United States. Eagles showed high fidelity to core wintering areas but plasticity in annual range sizes. Adult, migrant Golden Eagles used habitat types associated with perches and primary prey species. Golden Eagles chose areas within winter ranges that were close to prey habitat, within conifer forests and riparian areas, in relatively low elevations, and in areas conducive to orographic uplift. Golden Eagles appeared to avoid urban areas, grassland, agriculture, and non-sagebrush-steppe habitat types. Our results suggest that an effective conservation strategy for migrant Golden Eagles wintering in the western United States should include a large geographic area with heterogeneous habitat allowing for adequate hunting perches and prey habitat, with little urban development or anthropogenic habitat conversion.

Conservation Status of Diurnal Raptors in Venezuela
Adrián Naveda-Rodríguez

I here evaluate the conservation status of 64 species of diurnal raptors in Venezuela based on extent of occurrence (EOO) and area of occupancy (AOO) derived from geomatic-based geographic distribution modeling and gap analysis. I modeled the geographic distribution of raptor species to quantify distribution areas using the maximum entropy modeling techniques with nine environmental variables that were believed to influence the geographic distribution of raptors. The EOO and AOO were used to reevaluate the conservation status of diurnal raptors in Venezuela, applying Criteria B of the IUCN Red List. Furthermore, a gap analysis was performed to evaluate the effectiveness of strictly protected areas (SPA) in the conservation of birds of prey. EOO ranged from 10,423 km2 to 907,223 km2 and AOO values ranged from 6566 km2 to 903,193 km2; four species met the B1 criterion and are qualified to be reclassified. The gap analysis revealed that, on average, 20% and 24% of species’ EOO and AOO, respectively, were protected within SPA. In theory, SPA are assuming an effective role in the protection of species’ geographic distribution. Raptor conservation in Venezuela must be thoroughly planned; an update in land-use planning (territorial ordering) to enhance the connectivity among SPA would improve the protection of raptors.

Estimating Site Occupancy and Detection Probabilities for Cooper's and Sharp-Shinned Hawks in the Southern Sierra Nevada
Jennifer E. Carlson, Douglas D. Piirto, John J. Keane and Samantha J. Gill

Long-term monitoring programs that can detect a population change over time can be useful for managers interested in assessing population trends in response to forest management activities for a particular species. Such long-term monitoring programs have been designed for the Northern Goshawk (Accipiter gentilis), but not for the more elusive Sharp-shinned (A. striatus) and Cooper's hawks (A. cooperii). The objectives of this study were to (1) determine if it was possible to survey for these two Accipiters at the same time successfully using a new survey technique, and (2) estimate occupancy rate and detection probabilities for both species. We used broadcast surveys (BSM) to determine presence/absence for nesting Sharp-shinned and Cooper's hawks at Mountain Home Demonstration State Forest located in the southern Sierra Nevada mountain range in California. We surveyed 34 sampling units that were defined as the average home-range size (1000 m2) of the smallest target species, the Sharp-shinned Hawk. The sampling units were surveyed twice in 2003 and 3–4 times in 2004 during the breeding season. We used program PRESENCE to estimate detection probabilities and model occupancy rates for Sharp-shinned and Cooper's hawks. Our results indicated that the BSM using both Accipiter vocalizations in sequence was valuable for surveying both Sharp-shinned and Cooper's hawks. Proportions of the study area occupied for Sharp-shinned and Cooper's hawks were 0.25 (SE  =  0.079), and 0.40 (SE  =  0.098), respectively. The probabilities of detecting Cooper's and Sharp-shinned hawks at any given site were 0.56 (SE  =  0.098) and 0.47 (SE  =  0.086), respectively. There were no published occupancy estimates or detection probabilities in the literature to directly compare to our study. Because these species are elusive and difficult to survey, it is imperative future studies that address occupancy estimation for Sharp-shinned and Cooper's hawk incorporate detection probabilities into their model. Incorporating other variables into an occupancy model, such as habitat type, timber harvest, forest health, and/or climatic variables will also improve occupancy estimates.

Perennial Pair Bonds in an Accipiter: A Behavioral Response to an Urbanized Landscape?
Matthew A. Boggie, R. William Mannan and Craig Wissler

In some urban environments, human activities enhance resources for avian species, providing habitat that can support year-round occupancy. If both members of a mated pair stay on their breeding territories year-round, close proximity of pair members throughout the year may increase the potential for interactions outside the breeding season. Under these circumstances, avian species that would otherwise terminate their bonds following the breeding season may form perennial pair bonds. We examined behavior of mated pairs of adult Cooper’s Hawks (Accipiter cooperii) during the nonbreeding season in an urban environment to determine whether pairs retained their breeding territories outside the breeding season and if year-round maintenance of territories influenced the duration of pair bonds. Home ranges and core areas of pair members largely overlapped. Pair members remained close to the nest site they used during the previous breeding season, avoided neighboring conspecifics of the same sex, and selected areas within their home ranges that supported abundant avian prey and contained vertical vegetation structure. Pair members interacted throughout the nonbreeding season via acts of courtship and vocalizations, mainly in areas near the nest site. Perennial pair bonds in Cooper’s Hawks in this urban environment are likely a response to high availability of prey throughout the year and facilitated largely by fidelity to and retention of all-purpose territories year-round. For Cooper’s Hawks in this urban environment, maintaining pair bonds continuously may confer several advantages such as early initiation of breeding and higher reproductive success.

Relationship Between the North Atlantic Oscillation and Spring Migration Phenology of Broad-Winged Hawks (Buteo platypterus) At Hawk Mountain Sanctuary, 1998–2013
Han-Kyu Kim, Marta Sendra Vega, Marian Wahl, Chong Leong Puan, Laurie Goodrich and Keith L. Bildstein

Climatic factors influence migration behavior in both short- and long-distance migratory birds. The Broad-winged Hawk (Buteo platypterus) is a long-distance migrant that exhibits a regular calendar-like migration pattern, with some interannual variability during both the northbound and southbound migrations. We examined the relationship between the North Atlantic Oscillation (NAO) and the timing of spring migration in Broad-winged Hawks based on standardized migration count data collected at Hawk Mountain Sanctuary from 1998 to 2013. A strong negative correlation was found between a higher April NAO index and earlier passage dates for the first 50% (r  =  −0.723, P < 0.01) and 95% (r  =  −0.565, P  =  0.02) and mean passage date (r  =  −0.730, P < 0.01) of the hawks passing the watchsite. The April NAO values may serve as a useful indicator of the conditions encountered by Broad-winged Hawks during their northbound migration and our analyses suggest a possible climatic effect on their migration timing, as measured at the migration watchsites in the northeastern United States.

Body Size and Sexual Dimorphism in the Southernmost Subspecies of the Burrowing Owl (Athene cunicularia cunicularia
Alejandro V. Baladrón, Matilde Cavalli, Juan P. Isacch, María S. Bó and Enrique Madrid

We studied body size and sexual dimorphism in the southernmost subspecies of the Burrowing Owl (Athene cunicularia cunicularia) at the Pampas of Argentina, and we compared our data with those from other subspecies in the Americas. A total of 58 individuals were captured and their coloration pattern (plumage and bare parts), body linear measurements (wing chord, standard tail length, tarsus length and width, forearm length, exposed culmen length, and hallux claw length), and body mass were recorded. In addition, we banded each individual and took a blood sample from 44 individuals for molecular sex determination. In general, the body size measurements reported for A. c. cunicularia in this study agreed with previous reports based on museum specimens for the same subspecies, and were near the upper range for the species. In addition, tarsi of A. c. cunicularia were large in comparison to those of other subspecies. Sexes differed little in size, with tarsus length, tail length, and wing chord being slightly greater in males, and culmen length and mass slightly greater in females. However, mean values of these measurements did not differ statistically between sexes. The southernmost subspecies of Burrowing Owls, A. c. cunicularia, has a larger body size than the North American and Caribbean subspecies, which suggests geographical variation in body size of this species throughout its distributional range.

On the Breeding Biology of Northern Saw-whet Owls (Aegolius acadicus)
Jeffrey S. Marks, Ann Nightingale and Jenna M. McCullough

We monitored 37 Northern Saw-whet Owl (Aegolius acadicus) nesting attempts at the Boardman Tree Farm (BTF) in north-central Oregon from 2012 to 2015. Nests were initiated from early March to late June and contained an average of 5.7 eggs. Twenty-nine (78%) of the nesting attempts were successful and produced an average of 4.2 fledglings per successful attempt. One male paired with two females and produced 6 fledglings out of 10 eggs. We captured 59 unique nesting adults; 61% of the males (17 of 28) and 58% of the females (18 of 31) were second-year (SY) birds. We captured both adults at 30 nests: both parents were SYs at eight nests, both were after-second-year (ASY) at five nests, the female was SY and the male ASY at eight nests, and the male was SY and the female ASY at nine nests. Considering clutch size and number of young fledged, we found no evidence that pairs composed of SY parents reproduced less successfully than those composed of ASY parents. Sample sizes were small, but neither mean clutch size nor the mean number of young fledged differed significantly among nests of the four combinations of parental ages. One male and two females nested in more than one year; each obtained a new mate the second year. The first female had nested successfully in 2012 and settled in a box 3 km away in 2013; she abandoned her first clutch in 2013 and renested 15 d later in a different box with a male who also had nested successfully in 2012. The other female nested successfully in 2014 and settled in a box 3.7 km away in 2015. Of the 109 banded nestlings that fledged from 2012 to 2014, we encountered only one in a subsequent year through 2015. Our data suggest that breeding-site fidelity and natal philopatry are low in this population, as has been found elsewhere in western North America.

No comments:

Post a Comment