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Tuesday, 3 June 2014

Journal of Raptor Research: June 2014; Vol 48, Issue 2: Contents and Abstracts

Journal of Raptor Research
Published by: The Raptor Research Foundation

Table of Contents
Jun 2014 : Volume 48 Issue 2 


Home-Range Size and Examples of Post-Nesting Movements for Adult Golden Eagles (Aquila chrysaetos) in Boreal Sweden 

Edward H.R. Moss and Tim Hipkiss, Frauke Ecke, Holger Dettki, Per Sandström, Peter H. Bloom, Jeff W. Kidd, and Scott E. Thomas, Birger Hörnfeldt
pg(s) 93–105

We studied home-range size using 15 GPS-tracked adult Golden Eagles (Aquila chrysaetos) in nine different territories, two in 2011 and those two as well as seven others in 2012, in northern Sweden. Home ranges were represented by 50 and 95% minimum convex polygons (MCPs) and 50, 80 and 95% kernel density estimates (KDE). In 2012, 95% MCPs ranged from 100–525 km2 for males (n  =  8), and 60–605 km2 for females (n  =  7). Mean home-range sizes for the eagles in our study were among the largest reported. Moreover, we found an inverse relationship between home-range size and the percent of clear-cuts within the range. Together these suggest that eagles in Sweden may compensate for low availability of hunting areas, e.g., lower proportion of clear-cuts in their range, by expanding their range. Some eagles displayed different forms of post-nesting movements (i.e., movements not related to breeding) during the normal breeding season in addition to the ranging within their home ranges: (i) long-distance directional movements (n = 3), (ii) intermediate-distance movements (n = 4), and (iii) movements within an unusually large home range (n = 1). These movements varied considerably, with some eagles travelling nearly 700 km north into northern Finland and Norway. No adults with transmitters reproduced successfully in 2012; in four territories, nests failed and in five territories occupied by pairs we did not know if eggs were laid. Post-nesting movements, which occurred after nesting or breeding failure, occurred in a year with apparently low food supply and may have been triggered by local food shortage.

Association of Sex, Fledging Date, and Sibling Relationships with Post-Fledging Movements of Burrowing Owls in a Nonmigratory Population in the Imperial Valley, California 

Daniel H. Catlin, Daniel K. Rosenberg
pg(s) 106–117

Natal dispersal is an important driver of population and colonization dynamics, yet factors that affect timing and distance of post-fledging movements are poorly understood. We studied post-fledging movements of 34 (12 male and 22 female) juvenile Burrowing Owls (Athene cunicularia) between June 2002 and April 2003, in a nonmigratory population in the Imperial Valley, California. We found high variation in movement patterns among individuals. Juvenile Burrowing Owls left their nest throughout the year, with two females (6%) remaining within 100 m of their natal burrow until the beginning of the following year's breeding season. Juvenile Burrowing Owls moved up to 11.7 km (males: 397 ± 124 m; females 1762 ± 630 m) between emergence from the nest to the following breeding season. Those that fledged early in the season remained closer to their nests for a longer period than those that fledged later in the season. Female Burrowing Owls remained ≤100 m from their natal nests for a longer duration than males. Members of male–female, but not male–male, sibling pairs were more likely to be within 100 m of one another than members of female–female sibling pairs. After members of sibling pairs were >100 m apart, distance between members of sibling pairs was related only to time since fledging. Our study, conducted in a highly simplified agricultural environment, provides evidence that sex, fledging date, and sibling relationships can be responsible for the high individual variation in post-fledging movements of Burrowing Owls that has often been attributed to environmental variation.

Predicting Occurrence of Mexican Spotted Owls in Arid Canyonlands of Southern Utah 

David W. Willey, Mike Zambon
pg(s) 118–127

The Mexican Spotted Owl (Strix occidentalis lucida) was listed as “threatened” by the U.S. Fish and Wildlife Service in 1993. Predicting the distribution of suitable habitat is an important step in the owl's recovery, and Geographic Information Systems (GIS) provide appropriate spatial and analytic tools. We developed and validated a GIS-based occurrence model for Mexican Spotted Owls in arid canyon environments in Utah. We generated a set of competing models with topographic and vegetation covariates, and ranked models using information theory. Our top-ranked models indicated slope and variation in elevation were important predictors for the occurrence of Mexican Spotted Owls in rocky habitats, and we averaged coefficients from the top models to estimate probability of owl occurrence. During a model validation survey, we detected Spotted Owls in 22 test plots, where mean estimated probability of occurrence, an index to habitat suitability, was 0.68 (SE = 0.03). In addition, we evaluated model performance at 30 known Mexican Spotted Owl use sites from outside our model development areas, and observed an overall mean probability of occurrence equal to 0.78 (95% CI = 0.71–0.81). For the 30 known owl use sites, estimated probability of occurrence using our top model ranged from 0.54–0.90. Our results suggest that GIS modeling can be an important tool for predicting the potential distribution of Mexican Spotted Owls and their habitat in arid canyonlands in Utah.

Factors Associated with Flammulated Owl and Northern Saw-Whet Owl Occupancy in Southern Idaho 

Micah N. Scholer, Matthias Leu, James R. Belthoff
pg(s) 128–141

Spatially explicit models depicting species occupancy offer a useful conservation tool for land managers. Using occurrence data collected in 2009 and 2010 from the Boise National Forest, Idaho, we developed distribution models for Flammulated Owls (Psiloscops flammeolus) and Northern Saw-whet Owls (Aegolius acadicus) to explore associations between habitat factors and owl occupancy. We then spatially applied these models in a Geographic Information System. We considered land cover and topographic variables at three spatial scales: 0.4-km, 1-km, or 3-km-radius plots centered on point-count locations (n = 150) with resolution of land covers at 30 m. Flammulated Owls occupied 27 (18%) point-count locations and occurred in areas with a higher proportion of Douglas-fir (Pseudotsuga menziesii) at the 0.4-km scale, less diverse land cover composition at the 1-km scale, and in south-facing aspects at the 3-km scale. Northern Saw-whet Owls occupied 45 (30%) point-count locations and were associated with relatively flat terrain at the 0.4-km scale that had larger proportions of non-forest land cover. At the 1-km and 3-km scales, Northern Saw-whet Owls occurred in areas with south-facing aspects having a higher proportion of ponderosa pine (Pinus ponderosa), respectively. Biologists and land managers interested in the conservation of Flammulated Owls and Northern Saw-whet Owls can use our approach to delineate habitats important for these owls or to help identify locations suitable for restoration.

Home Range and Habitat Selection by the Tropical Screech-Owl in a Brazilian Savanna 

Fábio M. Barros and José C. Motta-Junior
pg(s) 142–150

The Tropical Screech-Owl (Megascops choliba) is a small nocturnal raptor that uses a large range of habitats throughout Brazil. Although it is one of the most abundant owls in the Neotropics, nothing has been published on its spatial ecology, and information on basic natural history is scarce. We followed four radio-tagged males to estimate home-range size and habitat selection in a savanna (cerrado) patch in southeastern Brazil. The mean (±SD) home-range size was 51.2 (26.9) ha using the 95% minimum convex polygon (MCP) method and 80.8 (40.2) ha using the 95% fixed kernel (FK) method. The mean (±SD) core area was 22.4 (8.8) ha (65% FK). During nocturnal activities, owls preferred semi-open (campo cerrado) and semi-closed (cerrado sensu stricto) habitats and avoided open habitats (campo sujo). Gallery forests and patches of invasive pines were preferred for roosting during the day. The variation in size of individual home ranges may be explained by individual's breeding status and habitat structure. Home-range sizes of Tropical Screech-Owls were generally similar to those of other screech-owls in North America, and the small differences in area requirements among species may be related to body mass and habitat structure.

Temporal Fluctuations in Raptor Abundances in Grasslands of Southeastern South America 

Felipe Zilio, Laura Verrastro and Márcio Borges-Martins
pg(s) 151–161
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We conducted 44 roadside surveys on grasslands landscapes of southern Brazil and Uruguay to study temporal changes in raptor abundance. Each route was surveyed twice in fall/winter and twice in spring/summer. Raptor abundance was higher during summer than winter, but did not differ between years. Thirteen of the 33 species recorded showed temporal changes in abundance, or are known to be migrants in the region. White-tailed Kite (Elanus leucurus), Yellow-headed Caracara (Milvago chimachima) and Southern Caracara (Caracara plancus) had higher abundance during fall/winter than spring/summer, which might be attributed to nomadic movements in agricultural landscapes. Changes in abundance of Savanna Hawk (Buteogallus meridionalis) and American Kestrel (Falco sparverius) suggest irruptive or nomadic movements. Turkey Vulture (Cathartes aura), Snail Kite (Rostrhamus sociabilis) and White-tailed Hawk (Geranoaetus albicaudatus) were more abundant in spring/summer than fall/winter, and our results suggest that they are partial migrants in the region. Variations in temperature, water level, and land use in agro-environment as well as dispersion, recruitment, and ephemeral concentration of food resources probably are the causes of fluctuation observed. Our results provide a starting point to better understand raptor temporal fluctuations and abundance in southeastern South America, but further investigations are required.

Northbound Migration Count of Raptors at Tanjung Tuan, Peninsular Malaysia: Magnitude, Timing, and Flight Behavior 

Chong Leong Puan, Chin Aik Yeap, Kim Chye Lim, Aun Tiah Lim, Swee Seng Khoo, and Nina Cheung
pg(s) 162–172

Tanjung Tuan is a primary spring raptor migration watchsite in Malaysia. During northbound migration, many raptors can be seen crossing the Straits of Malacca from Sumatra (Indonesia) to Peninsular Malaysia. We examined the migration magnitude, timing, and flight behavior of migratory raptors recorded based on migration counts at Tanjung Tuan in 2009 and 2010. A total of 37 615 migrating raptors of 11 species and 72 277 individuals of 10 species were counted in 2009 (332 hr of observation) and 2010 (465 hr), respectively. Eighty percent of bulk passage occurred in 29–38 d, with the average median passage date occurring in mid-March. Oriental Honey-buzzard (Pernis ptilorhyncus) made up 85.9 ± 2.9% of the flight, followed by Black Baza (Aviceda leuphotes, 8.7 ± 3.8%) and Chinese Goshawk (Accipiter soloensis, 3.0 ± 2.0%). The timing of the peak daily count differed among the three major migrants with highest count of Oriental Honey-buzzards occurring at 1200–1300 H, whereas for both Black Bazas and Chinese Goshawks, peak daily counts were at 1400–1600 H (when air temperatures were the highest). Most migration occurred during days when winds were from southwest and west. The difference in migration timing is believed to be associated with the species' flight behaviors, their preferred wind direction, and the availability of thermals. The height of flight for Oriental Honey-buzzards, which used both soaring and flapping flight during migration, was positively correlated with the hourly temperature (r = 0.241, P = 0.026). Results from migration counts made at Tanjung Tuan suggest that this watchsite captures a high proportion of migratory raptors (especially for Oriental Honey-buzzards) along the East Asian-Australasian flyway. Such information, together with count data collected from other watchsites, is essential for a better understanding of migratory raptors in this region and for effective conservation.

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