Synovial chondromatosis in raptors

Fourteen raptors, consisting of 13 great horned owls (Bubo virginianus) and one red-tailed hawk (Buteo jamaicensis), from central and north central Minnesota, western Wisconsin, and eastern South Dakota (USA) were admitted to a raptor rehabilitation center between June 1992 and June 1995, with perisynovial and synovial chondromatosis affecting multiple joints. Birds were severely debilitated primarily due to loss of shoulder motion. The etiology of these lesions in raptors is unknown.     

Complete mtDNA genome of Otus sunia (Aves,Strigidae) and the relaxation of selective constrains on Strigiformes mtDNA following evolution

Most of owls are nocturnal raptor and usually use their soft and fluffy feathers to flight silently to catch prey while other diurnal raptors prefer fierce attack and swift flight. For energy cost of these different hunting strategies can be greatly different, we speculate that mitochondrial gene of owls may undergo a different evolution pattern following raptors evolution. To test our hypothesis, we sequenced the mtDNA genome of Otus sunia and calculated the ratio of nonsynonymous to synonymous nucleotide substitutions (ω, Ka/Ks, dN/dS) of raptors. The mtDNA genome of O. sunia was 17,609 bp in length, containing 13 PCGs, 2 ribosomal RNAs, 22 transfer RNAs and a control region. Secondly structure of tRNAs and rRNAs were predicted and conserved sequence blocks (CSBs) on control region were identified. The Bayesian inference tree and maximum likelihood tree based on 13 PCGs and 2 rRNAs suggested the owls were related to other raptors. Finally, calculation of ω-values of each owls and other raptors mtDNA PCGs indicated that owls accumulated more nonsynonymous nucleotide substitutions relative to synonymous substitutions compared to other raptors. For mtDNA PCGs associated with energy metabolism, this finding may reveal the degeneration of flight abilities of owls.     

Covariation between bill colouration and fitness components in a nocturnal bird

Vividly coloured chromatic signals play a key role in social and sexual signalling in diurnal birds, but their role is considered negligible in favour of achromatic (i.e. white, pure grey and black colourations) signals in nocturnal species. Here we studied colour variation and potential signalling of the yellow bill – a trait functioning as sexual signal in diurnal raptors during the breeding season in females of a truly nocturnal raptor, the little owl Athene noctua. We found that yellow‐red chroma of the bill was highly variable between individuals and positively correlated with female fitness prospects (i.e. brood size at fledging). In addition, we found that females with brighter bills were larger in size and produced owlets with a higher mass at fledging. This study suggests that yellow bill colouration in female little owls may potentially play a role in sexual signalling and may constitute the first evidence of chromatic colour signalling in a nocturnal bird.     

Abundance of Diurnal Raptors in Relation to Prairie Dog Colonies: Implications for Bird-Aircraft Strike Hazard

Abstract: Some diurnal raptors are frequently observed at prairie dog (Cynomys sp.) colonies. As a result, some military installations have conducted prairie dog control activities to reduce the bird-aircraft strike hazard (BASH) potential of low-flying aircraft. To evaluate the validity of this management strategy, we assessed raptor associations with prairie dog colonies at 2 short-grass prairie study areas: southern Lubbock County, Texas, USA, and Melrose Bombing and Gunnery Range in east-central New Mexico, USA. We quantified diurnal raptors (i.e., Falconiformes) at plots occupied (colony plots) and unoccupied (noncolony plots) by black-tailed prairie dogs (Cynomys ludovicianus) at both sites throughout 2002. We compared the number of individual birds of a given species at colony and noncolony plots within each study area by season. Ferruginous hawks (Buteo regalis) and northern harriers (Circus cyaneus) were more abundant at colony plots, whereas Swainson's hawks (B. swainsoni) and American kestrels (Falco sparverius) were more abundant at noncolony plots. Red-tailed hawk (B. jamaicensis) abundance did not differ between the 2 plot types. Our results suggest prairie dog control as a method of reducing BASH potential may be effective at some sites but may be ineffective or even increase the BASH potential at others. Thus, bird-avoidance models assessing the BASH potential should be conducted on a site-specific basis using information on relative and seasonal abundances of individual raptor species and the relative strike risks they pose to aircraft.     

Pygmy owl Glaucidium passerinum and the usage of ultraviolet cues of prey

Birds rely mainly on their vision when foraging. Many diurnal raptors use ultraviolet (UV) vision and ultraviolet‐reflecting vole scent marks to find suitable hunting areas, whereas nocturnal owls seem to lack this ability. We studied if the diurnal pygmy owl Glaucidium passerinum that uses voles and birds as its food can detect vole scent marks using UV‐vision. We conducted a laboratory experiment with eleven owls. Each individual owl had four options to choose from: (1) scent marks with UV light, (2) scent marks without UV light, (3) clean arena with UV light and (4) clean arena without UV light. The owls scanned the scent mark arena more often in the presence of UV light than other arenas. However, owls did not spend more time above the UV arena. We suggest that pygmy owls can detect near UV and use UV to gain information about prey like other diurnal raptors.     

Raptors breeding on weaver nests in trees and on man-made structures

Several raptor species nest on top of large weaver nests. These weaver nests are usually sited in trees, but 11.7% of Red-billed Buffalo-Weaver Bubalornis niger and 25.7% of Sociable Weaver Philetairus socius nests occur on man-made structures. In an extensive literature search, a total of 16 raptor species were recorded as nesting on top of weaver nests. At least 10 raptor species used weaver nests built in trees. Seven raptor species used weaver nests on man-made sites and four raptor species only used weaver nests built on man-made sites. No owls have been recorded as using weaver nests on man-made sites. There are historical records of raptors nesting on top of weaver nests in trees, while nesting on top of weaver nests sited on man-made structures appears to be a more recent adaptation. Costs and benefits of nesting on man-made sites are briefly listed. Nesting on man-made sites may increase (by both weavers and raptors) and raptor researchers are encouraged to document cases of raptors nesting on weaver nests where these are placed in trees or artificial sites, so that there is a record of changes in frequency of nest site usage by raptors.     

Taphonomic study of leporid remains accumulated by the Spanish Imperial Eagle (Aquila adalberti)

Distinguishing leporid bones accumulated by different agents such as diurnal raptors, owls, mammals and humans is essential to gain an understanding of not only human subsistence activities but also past ecology. This is particularly relevant in Iberian Palaeolithic sites where leporid remains usually constitute the most abundant taxon. Among diurnal raptors the Spanish Imperial eagle (Aquila adalberti) has been one of the most important leporid predators throughout the Iberian Peninsula. In order to investigate the taphonomic signature of this raptor, rabbit remains from 79 pellets were examined. Results show a high proportion of distal elements of the limb bones and skull. Compared with other diurnal birds of prey, the assemblages produced by this species appear to show a higher degree of breakage and corrosion from digestion. These results place this predator within a category similar to the small mammal carnivores (category 5) in terms of skeletal element abundance, breakage and digestion. It is hoped that these data will enable analysts to identify leporid fossils accumulated by the Spanish Imperial Eagle in archaeological assemblages.     

First detection of Bacillus anthracis in feces of free-ranging raptors from central Argentina

Prevalence of anthrax spores in feces of raptors was determined from samples collected in November-December 2000 and April-May 2001 in an agricultural region of Santa Fé province, Argentina. Feces were tested from 48 birds of six raptor species. One of 14 chimango caracaras (Milvago chimango) and one of eight road-side hawks (Buteo magnirostris) tested positive. The prevalence of Bacillus anthracis spores in feces for the six species was 4% (n=48). The prevalence was 7% (n=14) for chimango caracaras, 13% for road-side hawks (n=8), and 0% for the remaining species (Burrowing owl [Speotyto cunicularia] [n=17], Swainson's hawk [Buteo swainsoni] [n=3], Aplomado falcon [Falco femoralis] [n=2], and American kestrel [Falco sparverius] [n=4]). Grouped by their feeding habits, prevalence for scavenger species was not significantly different than for predators (7% vs. 3%, P>0.999). This study provides evidence that in central Argentina scavenger and non-scavenger raptors may have a role in the epidemiology of anthrax. Long-term studies to determine the extent of this potential involvement in the epidemiology of anthrax in central Argentina are required.     

Diurnal exposure as a risk sensitive behaviour in tawny owls Strix aluco?

Tawny owls Strix aluco generally roost in cryptic locations during the day. To test the hypothesis that this cryptic behaviour is an effort to avoid mobbers or avian predators, we measured diurnal behaviour and cause-specific mortality of radio-tagged birds. Non-breeding adults (assumed to be well fed individuals, optimising their own survival) roosted in less exposed locations than adults with young and newly independent juveniles. Parents roosted in the most exposed sites when their young were immature and vulnerable to depredation, probably to guard offspring. Newly independent juveniles apparently selected roosting sites in exposed places to get access to food, as this behaviour was associated with lower perching heights and higher prey abundance beneath their roosting sites. They also perched in more exposed sites, closer to the ground, in summers with low prey abundance compared to summers with high prey abundance. After previous encounters with goshawks Accipiter gentilis , dependent juveniles roosted in less exposed places compared to other young. The increased risk of being mobbed was highly significant with increasing roosting exposure. Once an owl was mobbed, the intensity of the mobbing correlated positively with the mass of the mobbers, but mobbing birds never killed any owls. In contrast, diurnal raptors caused 73% of natural owl deaths (n=15) and the depredation rate by raptors was 3.8 times higher in population classes that generally roosted in more exposed locations than did non-breeding adults. We therefore suggest that depredation by diurnal raptors is the main factor shaping the diurnal behaviour of tawny owls.     

Role of prey and intraspecific density dependence on the population growth of an avian top predator

Exploring predator–prey systems in diverse ecosystems increases our knowledge about ecological processes. Predator population growth may be positive when conspecific density is low but predators also need areas with prey availability, associated with competition, which increases the risk of suffering losses but stabilises populations. We studied relationships between European rabbits Oryctolagus cuniculus (prey) and adult eagle owls Bubo bubo (predators) in south-western Europe. We assessed models explaining the predator population growth and stability. We estimated the abundance of rabbits and adult eagle owls during three years in eight localities of central-southern Spain. We explored models including rabbit and adult eagle owl abundance, accounting for yearly variations and including the locality as a random variable. We found that population growth of adult eagle owls was positive in situations with low conspecific abundance and tended to be negative but approaching equilibrium in situations of higher conspecific abundance. Population growth was also positively related to previous summer rabbit density when taking into account eagle owl conspecific abundance, possibly indicating that rabbits may support recruitment. Furthermore, abundance stability of adult eagle owls was positively related to previous winter–spring rabbit density, which could suggest predator population stabilisation through quick territory occupation in high-quality areas. These results exemplify the trade-off between prey availability and abundance of adult predators related to population growth and abundance stability in the eagle owl–rabbit system in south-western Europe. Despite rabbits have greatly declined during the last decades and eagle owls locally specialise on them, eagle owls currently have a favourable conservation status. As eagle owls are the only nocturnal raptor with such dependence on rabbits, this could point out that predators may overcome prey decreases in areas with favourable climate and prey in the absence of superior competitors with similar foraging mode.     

Abundance�Coccupancy relationships in metapopulations: examples of rock pool Daphnia

Intraspecific positive relationships between abundance and occupancy are observed for many species, suggesting that the same processes drive local and regional species dynamics. Two main groups of mechanisms explain this relationship: spatiotemporal variation in local population growth rates due to variation in habitat quality, or dispersal effects that increase occupancy of a species when locally abundant. Several studies show that spatiotemporal variation in population growth rates causes positive abundance?Coccupancy relationships, but few have shown dispersal effects. It is believed that such effects should be more evident for species whose dispersal is limited, e.g. metapopulations, but those studies are limited. This study investigates abundance?Coccupancy relationships in three Daphnia metapopulations in rock pools and the degree to which dispersal or habitat quality affect their local abundances and occurrence. Daphnia longispina and Daphnia magna showed positive abundance?Coccupancy relationships, but not Daphnia pulex. No single ecological factor could explain the abundance?Coccupancy relationships of any given species. Instead, dispersal processes and rock pool quality (mainly salinity and depth) seem to act together to shape the abundance?Coccupancy relationships. Such a conclusion is also supported by an immigration experiment in natural rock pools. This study suggests that although positive abundance?Coccupancy relationships may be commonly found for metapopulations, both dispersal processes and variation in habitat quality can be factors determining the abundance?Coccupancy relationship of metapopulations experiencing habitat heterogeneity.     

Intraspecific variation in reproductive traits of burrowing owls

Reviews of hatching asynchrony in birds recommended more studies on intraspecific variation in the extent of hatching asynchrony. We examined intraspecific variation in clutch size, laying chronology, onset of incubation, incubation period, and hatching asynchrony in burrowing owls (Athene cunicularia) in the Imperial Valley of California. Mean clutch size was 7.4 eggs and owls averaged 0.5 eggs laid per day. Females varied considerably in laying interval and onset of incubation (range?=?1st to 9th egg in the clutch). The mean incubation period was 21.9?days. Hatching interval also varied greatly among females ( $ \overline{x} $ ?=?0.8, range 0.1–2.0?days between successively hatched eggs). Past burrowing owl studies have largely overlooked the substantial intraspecific variation in these traits or have reported estimates that differ from ours. Future studies designed to identify the environmental factors that explain the large intraspecific variation in these traits will likely provide insights into the constraints on local abundance.     

The numerical response of breeding Northern Saw-whet Owls Aegolius acadicus suggests nomadism

We used a 13-year time series of abundance estimates of breeding Northern Saw-whet Owls (Aegolius acadicus), and of small mammals from central Ontario, Canada, to assess the numerical response of the owls to small-mammal prey species. We found that the finite rate of increase of breeding owls was directly related to estimates of red-backed vole (Myodes gapperi) abundance. Thus, it appeared that the owls were nomadic, and made decisions about where to breed based on vole supply. The owls showed a much weaker response to deer mouse (Peromyscus maniculatus) abundance. Across all years, 55% of variation in owl rate of increase could be uniquely attributed to vole abundance, whereas only 3% could be attributed to mouse abundance. Consistent with the model of nomadism, there was only a weak relationship between the proportion of hatch-year owls caught at fall banding stations, and small-mammal abundance. Instead, it appeared that Northern Saw-whet Owls avoided years of widespread reproductive failure through the nomadic strategy of selecting breeding sites based on vole supply.     

Higher nest predation risk in association with a top predator: mesopredator attraction?

Breeding close to top predators is a widespread reproductive strategy. Breeding animals may gain indirect benefits if proximity to top predators results in a reduction of predation due to suppression of mesopredators. We tested if passerine birds gain protection from mesopredators by nesting within territories of a top predator, the Ural owl (Strix uralensis). We placed nest boxes for pied flycatchers (Ficedula hypoleuca) in Ural owl nest sites and in control sites (currently unoccupied by owls). The nest boxes were designed so that nest predation risk could be altered (experimentally increased) after flycatcher settlement; we considered predation rate as a proxy of mesopredator abundance. Overall, we found higher nest predation rates in treatment than in control sites. Flycatcher laying date did not differ between sites, but smaller clutches were laid in treatment sites compared to controls, suggesting a response to perceived predation risk. Relative nest predation rate varied between years, being higher in owl nest sites in 2 years but similar in another; this variation might be indirectly influenced by vole abundance. Proximity to Ural owl nests might represent a risky habitat for passerines. High predation rates within owl territories could be because small mesopredators that do not directly threaten owl nests are attracted to owl nest sites. This could be explained if some mesopredators use owl territories to gain protection from their own predators, or if top predators and mesopredators independently seek similar habitats.     

Mechanisms determining the spatial distribution of microtine predators on the Arctic tundra

1. We studied the spatial distribution of avian microtine predators using data from 19 study areas on the tundra of northern Siberia.
2. Numbers of snowy owls, and long-tailed skuas and pomarine skuas depended strongly on lemming density. However, a significant relationship between lemming density and number of rough-legged buzzards appeared first after removal of the effect of snowy owl abundance on the distribution of rough-legged buzzards.
3. We applied a recently developed method (Manly 1995) to examine co-occurrences of species and found that rough-legged buzzards and snowy owls did not co-occur while snowy owls, long-tailed skuas and pomarine skuas did.
4. There are large differences in nest construction and chick behaviour between rough-legged buzzards and the three other species. Moreover, the snow owl is a polyphagous predator preying also on large birds including raptor chicks. Therefore, we propose that reduced risk of nest predation favours rough-legged buzzards nesting away from snowy owls.
5. Variations in abundance of the two lemming species did not seem to influence the distributions of snowy owls and rough-legged buzzards. Neither was it likely that latitudinally related factors such as breeding season length affected the distribution of rough-legged buzzards.     

Site Occupancy Dynamics of Northern Spotted Owls in the Eastern Cascades,Washington, USA, 1990–2003

Abstract: Northern spotted owls (Strix occidentalis caurina) have received intense research and management interest since their listing as a threatened species by the United States Fish and Wildlife Service in 1990. Several spotted owl (Strix occidentalis) response variables have been examined in various investigations, but recent advances in statistical modeling permit evaluations of temporal and spatial variability in site occupancy, local-extinction, and colonization probabilities while incorporating imperfect detection probabilities. Following recent work by other researchers on site occupancy dynamics of spotted owls in Oregon, USA, we evaluated temporal variability of detection, occupancy, local-extinction, and colonization probabilities for spotted owls, as well as potential influences of barred owl (Strix varia) presence on these parameters. We used spotted owl survey data collected from 1990 to 2003 on a study area in the eastern Cascades Mountains, Washington, USA, to compare competing occupancy models from Program PRESENCE using Akaike's Information Criterion. Detection probabilities for individual spotted owls ranged from 0.54 to 0.80 if barred owls were not detected during the survey season and from 0.19 to 0.71 if barred owls were detected during the survey season. Pair detection probabilities ranged from 0.27 to 0.67 if barred owls were not detected during an individual survey and from 0.09 to 0.36 if barred owls were detected during an individual survey. During the study, site occupancy probabilities for spotted owl pairs declined by approximately 50%. For all spotted owls, both singles and pairs, site occupancy probabilities declined moderately during the study. Barred owl presence was negatively associated with spotted owl detection probabilities, and it had a positive association with local-extinction probabilities for all spotted owls, both singles and pairs. Given that our study area has supported higher densities of barred owls for longer periods than other study areas, our results may provide insight into how barred owls have influenced spotted owl site occupancy dynamics in adjacent British Columbia, Canada, or will influence spotted owl site occupancy dynamics in Oregon and California, USA, in the future.     

Geographic patterns of species richness of diurnal raptors in Venezuela

Knowledge of a species’ geographic distribution is crucial to assessing its vulnerability. It is also important to know if protected areas provide effective protection for raptor species. Here, we examine the species richness (S) patterns, factors predicting S and the effectiveness of protected areas (EPA) in the conservation of diurnal raptors in Venezuela. We modeled geographic distributions (SDM) of 64 raptor species using ecological niche models. Nine climatic and seven landscape metrics were used as environmental predictors. SDM were stacked to examine S and predictors of S were investigated using regression models. This study evaluated S patterns in the 13 bioregions defined for Venezuela. A gap analysis was performed to evaluate the EPA in the conservation of raptor diversity. Forty species showed a continuous distribution, whereas as disjunct distributions were observed in 24 species. Species richness differed among bioregions; six pairwise compared bioregions did not show differences. Guyana Massif and the mountains of northern Venezuela had the highest species richness. Landscape features, specifically canopy height, land cover and terrain slope explained most of the species richness. Environmental heterogeneity affected the distribution of S and is therefore important in conservation planning for Neotropical raptors. Responses from environmental variables used to predict S were scale dependent; it is necessary to standardize methods/experimental design to study the biogeography of raptors. Priority-setting for the conservation of raptors in Venezuela must consider restricted range species, even if they are not threatened. A new territorial ordering is urgent to improve the protection of this group of birds.     

Health of an ex situ population of raptors (Falconiformes and Strigiformes) in Mexico: diagnosis of internal parasites

Successful programs for ex situ and in situ conservation and management of raptors require detailed knowledge about their pathogens. The purpose of this study was to identify the internal parasites of some captive raptors in Mexico, as well as to verify their impact in the health status of infected birds. Birds of prey were confiscated and kept in captivity at the Centro de Investigación y Conservación de Vida Silvestre (CIVS) in Los Reyes La Paz, Mexico State. For this, fecal and blood samples from 74 birds of prey (66 Falconiformes and eight Strigiformes) of 15 species, juveniles and adults from both sexes (39 males and 35 female), were examined for the presence of gastrointestinal and blood parasites. Besides, the oropharyngeal cavity was macroscopically examined for the presence of lesions compatible with trichomoniasis. Among our results we found that lesions compatible with Trichomonas gallinae infection were detected only in two Red-tailed hawks (Buteo jamaicensis) (2.7%); nevertheless, infected birds were in good physical condition. Overall, gastrointestinal parasites were found in 10 (13.5%) raptors: nine falconiforms (13.6%) and one strigiform (12.5%), which mainly presented a single type of gastrointestinal parasite (90%). Eimeria spp. was detected in Harris's hawk (Parabuteo unicinctus), Swainson's hawk (Buteo swainsoni), Red-tailed hawk (B. jamaicensis) and Great horned owl (Bubo virginianus); whereas trematodes eggs were found in Peregrine falcon (Falco peregrinus) and Swainson's hawk (B. swainsoni). Furthermore, eggs of Capillaria spp. were found in one Swainson's hawk (B. swainsoni), which was also infected by trematodes. Hemoprotozoarian were detected in five (6.7%) falconiforms: Haemoproteus spp. in American kestrel (F. sparverius) and Leucocytozoon spp. in Red-tailed hawk (B. jamaicencis). Despite this, no clinical signs referable to gastrointestinal or blood parasite infection were observed in any birds. All parasites identified were recorded for the first time in raptors from Mexico. Furthermore, this represents the first report for T. gallinae, trematodes, Haemoproteus spp. and Leucocytozoon spp. in raptors from Latin America. Diagnosis and control of parasitic infections should be a part of the routine in health care evaluations for ex situ raptor populations. Finally, this information is also valuable for in situ conservation actions on these birds.     

A comparative study of the mechanics of the pectoralis muscle of the red‐tailed hawk and the barred owl

A comparison of the isometric forces and levers of the pectoralis muscle in red‐tailed hawks (Buteo jamaicensis) and barred owls (Strix varia) was done to identify differences that may correlate with their different flight styles. The pectoralis consists of two heads, the anterior m. sternobrachialis (SB) and the posterior m. thoracobrachialis (TB). These are joined at an intramuscular tendon and are supplied by separate primary nerve branches. As in other birds, the two heads have distinct fiber orientations in red‐tailed hawks and barred owls. SB's fiber orientation (posterolateral and mediolateral from origin to insertion) provides pronation and protraction of the humerus during adduction. Electromyographic studies in pigeons show that it is active in early downstroke and during level flight. TB is more active during take‐off and landing in pigeons. The anterolateral orientation (from origin to insertion) of its fibers provides a retractive component to humeral adduction used to control the wing during landing. In our study, the maximum isometric force produced by the combined pectoralis heads did not differ significantly between the hawk and owl, however, the forces were distributed differently between the two muscle heads. In the owl, SB and TB were capable of producing equal amounts of force, but in the hawk, SB produced significantly less force than did TB. This may reflect the need for a large TB to control landing in both birds during prey‐strike, with the owl maintaining both protractive (using SB) and retractive (using TB) abilities. Pronation and protraction may be less important in the flight behavior of the hawk, but its prey‐strike behavior may require the maintenance of a substantial TB for braking and controlled stalling, as it initiates strike behavior. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc.