Burrowing Owl Research Articles

Captive-reared burrowing owls show higher site-affinity, survival, and reproductive performance when reintroduced using a soft-release

A remaining challenge for animal reintroductions is how best to aid individuals transitioning from captivity into the wild. We tested two techniques – ‘soft’ vs. ‘hard’ release – in a 7-year study on endangered Western burrowing owls ( Athene cunicularia hypugaea) in British Columbia, Canada. Traditionally, captive-reared yearling adults were released into the wild, as pairs, directly from artificial burrows (hard-release). Only 46% of 201 owls released in this way (2001–2004) stayed at release sites. To test for improved success, soft-releases were performed in the same manner as concurrent hard-releases (2005–2007), except above-ground enclosures confined each soft-release pair to the vicinity of their burrow for 2 weeks before complete release. Of 140 soft-released owls, 86% stayed at release sites; whereas, 66% of 100 hard-released owls stayed. Breeding-season survival was 70% for soft-released owls vs. 50% for hard-released owls. On average, soft-released owls produced 50% more fledglings than concurrently hard-released owls. Post-fledging survival was 69% and first-year return rate was 7.0% for fledglings from soft-released parents, compared to 50% and 4.0% for fledglings from hard-release parents. Ultimately, 0.17 offspring were recruited into the local wild breeding population per soft-released pair, compared to 0.05 local recruits per hard-released pair. We recommend that enclosure-based soft-releases be used for reintroduction of burrowing owls in British Columbia and elsewhere in North America. We encourage other tests for improved release success with soft-releases, particularly for species with a high tendency for dispersal or those likely to experience significant predation pressure.

A case of leucism in the burrowing owl Athene cunicularia (Aves: Strigiformes) with confirmation of species identity using cytogenetic analysis

Leucism is an inherited disorder, characterized by the lack of pigments in part or all of the body, normal coloration of the eyes and, in birds, in naked parts such as the bill and legs. This kind of disorder is sometimes erroneously designated as albinism or partial albinism. In this study, we present a case of leucism in a wild owl. The studied individual presented completely white plumage, light-yellow coloration of legs and bill and normal coloration of eyes. According to morphological features, this owl is a specimen of burrowing owl, Athene cunicularia (Molina, 1782). To confirm the species identity, we used cytogenetic analyses for karyotypic determination, comparing it to the previously described one in the literature. We also studied a captive female of A. cunicularia to complement the species karyotype, which was described in the literature based only on a single male. The karyotype of the leucistic owl individual was compatible with the previously published one for A. cunicularia, confirming the bird was a male specimen. Cytogenetic analysis of the captive female showed that the W sex chromosome is metacentric and comparable to the seventh pair in size. This is the first description of a case of leucism in A. cunicularia for South America. Long-term studies are needed in the Neotropical region to evaluate survival and breeding success in leucistic birds.

Occurrence and Habitat Characteristics of Burrowing Owl Nests in Gunnison's Prairie Dog Colonies of Northeastern Arizona

Because Burrowing Owls (Athene cunicularia) often nest in colonies of prairie dogs (Cynomys sp.), recent declines of Gunnison's prairie dogs (Cynomys gunnisoni) could adversely affect this owl, considered uncommon in northern Arizona. In 2005, we determined the colony size and burrow density of 33 active Gunnison's prairie dog colonies in grasslands of northeastern Arizona. In 2006, we surveyed these colonies to determine the presence and relative abundance of Burrowing Owls, monitored nests to estimate nest success and productivity, and studied habitat characteristics at Burrowing Owl nest burrows. The 33 mapped colonies had a mean colony size of 16.6 ha and mean burrow densities of 57.7 active burrows/ha and 122.9 total burrows/ha. Seventeen nesting pairs of Burrowing Owls were associated with 12 of 33 (36%) prairie dog colonies, producing an average of 1.7 young per nest. Burrowing Owl presence at a prairie dog colony was not related to colony size or burrow density. Occurrence of an owl nest within a prairie dog colony was positively correlated with the mean number of active prairie dog burrows, total burrows, and percent of active burrows within 50 m, and negatively correlated with distance to the nearest active and inactive prairie dog burrow, elevation, and percent slope. Eight of 17 (47%) Burrowing Owl nests were successful, with brood size averaging 5.4 young per successful nest 25–31 days after hatching. Successful nests had fewer active, inactive, and total prairie dog burrows within 50 m than unsuccessful nests, contrary to previous findings. Successful nests also were closer to the nearest road than failed nests.

Tracking movements of Athene owls: the application of North American experiences to Europe

Migration and dispersal are important ecological and evolutionary processes and understanding them is a requirement for species conservation efforts. Burrowing owl, Athene cunicularia, the North American equivalent of little owl, A. noctua, is migratory in the northern parts of its range. In Canada their populations have declined dramatically and are classified as endangered. Movements of burrowing owls have been studied using banding (ringing), VHF telemetry, stable isotopes, genetics (DNA), geolocators and satellite transmitters. Geolocators and satellite transmitters provide the most reliable information about migrations but to operate successfully they are both dependent upon exposure to sunlight, which can be limited for nocturnal owls. Ringing encounters and winter influxes of little owls into Spain, including the Balearic Islands, indicate that some migration movement may be occurring. A stable isotope study could determine if wintering owls in southern Europe includes owls originating in northern Europe.

Collection of Mammal Manure and Other Debris By Nesting Burrowing Owls

Burrowing Owls (Athene cunicularia) routinely collect and scatter dry manure of mammals around their nesting burrows. Recent studies have suggested this behavior attracts insect prey to the nesting burrow. However, some Burrowing Owls do not use manure, but instead, collect and scatter other materials (e.g., grass, moss, paper, plastic) around their nesting burrow in a similar fashion. Use of these materials seemingly contradicts the prey-attraction hypothesis. Using observational and experimental methods, we tested whether Burrowing Owls preferred manure to other materials commonly found at nesting burrows in eastern Washington. We found a wide variety of materials at nests, but grass and manure were the most common materials. The amount of manure present at nests was negatively correlated with the amount of other materials, and with the distance to the nearest source of manure. Burrowing Owls showed no preference between horse manure and grass divots at experimental supply stations that we placed near nesting burrows. They did prefer these two materials to carpet pieces and aluminum foil (both materials that are often found at Burrowing Owl nests). Our results did not support the premise that Burrowing Owls specifically seek out manure when lining their nesting burrows. The unusual behavior of collecting and scattering mammal manure and other debris at Burrowing Owl nests may serve functions other than (or in addition to) prey attraction and alternative hypotheses need further testing before the function of this behavior is certain.

Factors Affecting the Presence of Nesting Burrowing Owls in an Agricultural Landscape

Abstract We examined factors that influenced the presence of nesting Western Burrowing Owls (Athene cunicularia hypugaea) along roadsides and irrigation water-conveyance systems within an intensive agricultural area in Imperial Valley, southeastern California. We conducted walking line-transect surveys along randomly selected 1-km segments of roads to examine the types of roadside attributes and agricultural crops that were associated with the presence of nesting Burrowing Owls. Occupied burrows were more likely to be located along roadsides adjacent to fields where crops were present, but we found no obvious association with any particular type of crop. However, the type (concrete delivery canal or earthen drainage ditch), number, and location of irrigation trenches between the road and the agricultural field affected the likelihood of detecting owl nests. We failed to detect any effect of trench depth or whether the road was paved on the presence of Burrowing Owls. We found more occupied burrows on road...

Winter Destinations and Habitats of Canadian Burrowing Owls

Abstract The winter destination of Burrowing Owls (Athene cunicularia) that breed in Canada is poorly understood. We flew 166.7 hr in a fixed-wing CESSNA 172, searching southern Texas and the Gulf Coast lowlands and central Mexico for signals from 125 VHF transmitters that were attached to Burrowing Owls in Canada in 1997, 1998, and 2000. Nine owls were located between Houston, Texas, and Michoacan, Mexico. The diurnal roosts used by the owls included vegetation, natural burrows, and a woodpile. Land-cover types around roosts were highly variable and less open than breeding habitat in Canada, but always included at least 35% low vegetation within 1 km of roosts.

Parcel-based classification of agricultural crops via multitemporal Landsat imagery for monitoring habitat availability of western burrowing owls in the Imperial Valley agro-ecosystem

Agricultural production has a large impact upon the sustainability of wildlife populations. Certain species decline in the presence of intensive agriculture, while others thrive. Thus, quantifying changes in habitat within agricultural systems is paramount to understanding the underlying ecological mechanisms influencing species' range shifts and may facilitate the development of management strategies for sensitive wildlife species that depend on agricultural systems. Remotely sensed data can provide an efficient means to assess and monitor agricultural crop dynamics across large spatial extents. The objective of this study was to classify field-level agricultural crop types via a time series of Landsat imagery across the 3 620 000 ha agro-ecosystem in the Imperial Valley in California. The primary impetus was to generate data to characterize short-term changes in habitat for the western burrowing owl (Athene cunicularia), a species of concern that has an affinity for agricultural systems. The parcel-based classification method attained overall accuracies of 84% and 69% for level II (3 crop groups) and level III (31 crop types) agricultural crops, respectively. Given the large number of crop categories classified, these accuracies were quite high, especially when compared with existing crop type classifications across the region (e.g., the National Cropland Data Layer). These results suggest that the crop type classifications presented herein could potentially be used to evaluate owl demographic and space use parameters in light of shifting crop patterns across the study area.

Miscellaneous ecological notes on Brazilian birds of prey and owls

Sixteen opportunistic field observations of eight species of Brazilian raptors (Falconiformes and Strigiformes) are reported here as a contribution to the knowledge of the natural history of these poorly studied birds in Brazil. The observations are related to the food habits (Buteo albicaudatus, Herpetotheres cachinnans, Milvago chimachima, Falco femoralis), reproduction (Asio stygius, Megascops choliba), mobbing behaviour elicited in other birds (Geranospiza caerulescens, H. cachinnans, F. femoralis, A. stygius, Athene cunicularia) and a rare case of leucism in owls (A. cunicularia).

Bioecology of the Ghost CrabOcypode quadrata(Fabricius, 1787) (Crustacea: Brachyura) Compared with Other Intertidal Crabs in the Southwestern Atlantic

Data sets on the natural dynamics of beach ecosystems arc scarce and fragmentary. Such data arc necessary for implementing more efficient monitoring programs that quantify the dynamics of key ecological attributes on sandy beaches. This article contributes to the bioecology of ghost crabs from subtropical Praia Brava, Itajaí, Santa Catarina. Ocypode quadrata occurs in sandy beaches along the tropical-temperate western Atlantic, from Rhode Island (US) to Rio Grande do Sul (Brazil). During 14 consecutive months, a total of 649 specimens were captured: 255 females (39%), 241 males (37%), and 153 juveniles of undetermined sex (24%). Highest densities were recorded in June and November, with a total of 1,900 burrows distributed along the beach (56.95%) and dunes (43.05%). Sixteen natural diet items were identified for this crab, with a larger participation of Apis spp. (38.97% of relative volume). In the local food web, the ground-burrowing owl Speotyto cunicularia was the main crab predator. This article indicates that the ghost crab represented the second most consumed food item of the owl (29.24%), only surpassed by rodent remains, which occupied 50.32% of its stomach volume. The natural diet and the main predator of the ghost crab had not been observed along the coast of Brazil. Knowledge of natural diet is fundamental for understanding distribution patterns, migrations, and molting cycles. Further information on population structure (abundance peaks in spring and summer; a negative allometric growth pattern), spatial distribution (predominance of females in August and May, and of males in July; size of specimens increases toward higher intertidal levels), sexual proportion throughout the year (reproduction is continuous), form and disposition of burrows (reduced abundance toward the higher tidal levels), and relative importance for the diet of the main predator (both predator and prey arc nocturnal) may be used as instruments for evaluating the occupational impact and for conserving natural dune and beach environments along sandy beach ecosystems. In conclusion, ghost crabs provide an alternative source of food for the ground-burrowing owl, a predator that may represent an important population controlling factor, other than the human-induced impacts on sandy beaches. Although burrowing crabs are the most conspicuous and ecologically important invertebrates of intertidal beaches along tropical and temperate regions, factors that regulate abundance arc still controversial, whereas the biotic community interactions in sandy beaches remain barely known.

Diet of the Burrowing Owl (Athene cunicularia) and its seasonal variation in Patagonian steppes: implications for biodiversity assessments in the Somuncurá Plateau Protected Area, Argentina

A wide literature exists on the food habits of the Burrowing Owl (Athene cunicularia) in South America. However, this information is scarce for the arid lands of Argentina. Owl's diet composition in the Somuncurá Plateau and its seasonal variations were estimated. The Somuncurá landscape is a volcanic plateau conformed by superimposed layers of basalt flows. The climate is arid and cold and the vegetation is characterized by a grassy steppe of the Patagonian Phytogeographical Province. Pellets were collected during late spring and late summer around two lagoons from upper elevations (41°25′35″S, 66°57′27″W, 1412 m a.s.l.). These were measured, dissected and prey were identified and quantified. Sample richness, biomass and food-niche breadth were calculated as dietary parameters. Small mammals availability was estimated by trapping. The Burrowing Owl showed a generalist diet, including a wide variety of prey from invertebrates to vertebrates. Coleopterans were dominant in the spring diet, while rodents and arachnids became important in the late summer diet. The high species richness detected in this study through the analysis of raptor pellets is valuable for biodiversity assessments of unexplored areas such as Somuncurá.

Novel Scavenger Removal Trials Increase Wind Turbine—Caused Avian Fatality Estimates

ABSTRACT For comparing impacts of bird and bat collisions with wind turbines, investigators estimate fatalities/megawatt (MW) of rated capacity/year, based on periodic carcass searches and trials used to estimate carcasses not found due to scavenger removal and searcher error. However, scavenger trials typically place ≥10 carcasses at once within small areas already supplying scavengers with carcasses deposited by wind turbines, so scavengers may be unable to process and remove all placed carcasses. To avoid scavenger swamping, which might bias fatality estimates low, we placed only 1–5 bird carcasses at a time amongst 52 wind turbines in our 249.7‐ha study area, each carcass monitored by a motion‐activated camera. Scavengers removed 50 of 63 carcasses, averaging 4.45 days to the first scavenging event. By 15 days, which corresponded with most of our search intervals, scavengers removed 0% and 67% of large‐bodied raptors placed in winter and summer, respectively, and 15% and 71% of small birds placed in winter and summer, respectively. By 15 days, scavengers removed 42% of large raptors as compared to 15% removed in conventional trials, and scavengers removed 62% of small birds as compared to 52% removed in conventional trials. Based on our methodology, we estimated mean annual fatalities caused by 21.9 MW of wind turbines in Vasco Caves Regional Preserve (within Altamont Pass Wind Resource Area, California, USA) were 13 red‐tailed hawks (Buteo jamaicensis), 12 barn owls (Tyto alba), 18 burrowing owls (Athene cunicularia), 48 total raptors, and 99 total birds. Compared to fatality rates estimated from conventional scavenger trials, our estimates were nearly 3 times higher for red‐tailed hawk and barn owl, 68% higher for all raptors, and 67% higher for all birds. We also found that deaths/gigawatt‐hour of power generation declined quickly with increasing capacity factor among wind turbines, indicating collision hazard increased with greater intermittency in turbine operations. Fatality monitoring at wind turbines might improve by using scavenger removal trials free of scavenger swamping and by relating fatality rates to power output data in addition to rated capacity (i.e., turbine size). The resulting greater precision in mortality estimates will assist wildlife managers to assess wind farm impacts and to more accurately measure the effects of mitigation measures implemented to lessen those impacts.

Fire management and the nesting of Athene cunicularia (Aves, Strigidae) in grasslands in central Cerrado, Brazil

Fire management is a common practice in several reserves in the Cerrado, but its influences on bird reproduction remain unknown. In addition, the nesting biology of the Burrowing Owl (Athene cunicularia) has been studied in numerous environments, but not in tropical grasslands managed by fire. This study examined the effects of fire management on the nesting biology of A. cunicularia in Emas National Park, State of Goias, central Brazilian Cerrado. We compared the number of breeding pairs and their burrows in October and November 2009 at 15 study sites in grasslands managed by fire (firebreaks) and unmanaged grasslands adjacent to and distant from firebreaks. We visited active burrows two-four times and described the burrow entrances and sentinel sites and counted and observed adults and young. A total of 19 burrows were found at firebreaks. One and two burrows were found in grasslands adjacent to and distant from firebreaks, respectively. For all burrows found, one to three young reached the adult size, being able to fly and/or run in early November. The 22 burrows found were in the ground, associated or not with termite and ant nests. Most (86.4%) burrows had only one entrance. Only three burrows had two or three entrances. Structures used as sentinel perches by adults were mounds in front of the burrow entrances, termite nests, shrubs and trees. Most of these sentinel sites were shorter than 2 m high and located less than 10 m from the burrow entrance. At Emas National Park, firebreaks appear to provide more attractive conditions to the nesting of A. cunicularia than unmanaged grasslands, likely because of the short herbaceous stratum due to frequent burning of firebreaks. This study suggests that fire management provides suitable conditions for the successful reproduction of A. cunicularia in firebreaks at Emas National Park.

Avifauna of the Sipaliwini Savanna (Suriname) with Insights into Its Biogeographic Affinities

Ornithological surveys of the Sipaliwini savanna, an Amazonian savanna enclave along the Suriname—Brazil border, were conducted in July 2006 and June 2007. Of the 148 species recorded, five are new for Suriname: Micropygia schomburgkii, Myiopagis vindicata, Sublegatus modestus, Neopelma pallescens and Neothraupis fasciata. Patterns of species-sharing are compared among the Sipaliwini, other Amazonian savanna enclaves, and the large savanna complexes of the Llanos and Cerrado. In the Sipaliwini, forest birds are a subset of the Guiana Shield avifauna, while openhabitat species are shared predominantly with the Cerrado. Furthermore, the Sipaliwini populations of Falco sparverius and Athene cunicularia are identified as belonging to Cerrado subspecies instead of those occurring in nearby Guyana. The results support the hypothesis that the Sipaliwini and Amapá savannas were once connected to the Cerrado, likely by a coastal corridor.

Eighteen microsatellite loci developed from western burrowing owls (Athene cunicularia hypugaea)

Western burrowing owls (Athene cunicularia hypugaea) are ground-dwelling owls distributed through- out western North America. Because of population declines, this species is considered endangered in Canada, and burrowing owls are listed as a species of conservation concern in states of the western USA. Korfanta et al. (2002) previously presented primers for seven microsatel- lite loci in burrowing owls. Parentage and relatedness studies require a larger number of markers for accuracy and precision. Here, we developed and characterized 18 addi- tional microsatellite DNA loci, and we tested these loci in 23 individuals. The number of alleles per locus ranged from 2 to 11; two loci deviated from Hardy-Weinberg equilibrium following Bonferroni correction; we did not detect linkage disequilibrium following Bonferroni cor- rection; and the probability of exclusion for parent pairs using all loci was (0.9999. We envision these loci will facilitate detailed analyses of the genetic mating system of burrowing owls, which is poorly understood.

Estimates of Density, Detection Probability, and Factors Influencing Detection of Burrowing Owls in the Mojave Desert

We estimated relative abundance and density of Western Burrowing Owls (Athene cunicularia hypugaea) at two sites in the Mojave Desert (2003–04). We made modifications to previously established Burrowing Owl survey techniques for use in desert shrublands and evaluated several factors that might influence the detection of owls. We tested the effectiveness of the call-broadcast technique for surveying this species, the efficiency of this technique at early and late breeding stages, and the effectiveness of various numbers of vocalization intervals during broadcasting sessions. Only 1 (3%) of 31 initial (new) owl responses was detected during passive-listening sessions. We found that surveying early in the nesting season was more likely to produce new owl detections compared to surveying later in the nesting season. New owls detected during each of the three vocalization intervals (each consisting of 30 sec of vocalizations followed by 30 sec of silence) of our broadcasting session were similar (37%, 40%, and 23%; n = 30). We used a combination of detection trials (sighting probability) and double-observer method to estimate the components of detection probability, i.e., availability and perception. Availability for all sites and years, as determined by detection trials, ranged from 46.1%–58.2%. Relative abundance, measured as frequency of occurrence and defined as the proportion of surveys with at least one owl, ranged from 19.2%–32.0% for both sites and years. Density at our eastern Mojave Desert site was estimated at 0.09 ± 0.01 (SE) owl territories/km2 and 0.16 ± 0.02 (SE) owl territories/km2 during 2003 and 2004, respectively. In our southern Mojave Desert site, density estimates were 0.09 ± 0.02 (SE) owl territories/km2 and 0.08 ± 0.02 (SE) owl territories/km2 during 2004 and 2005, respectively.

OCCURRENCE OF WEST NILE VIRUS INFECTION IN RAPTORS AT THE SALTON SEA, CALIFORNIA

We investigated the prevalence of West Nile virus (WNV)-neutralizing antibodies and infectious virus, and the occurrence of overwinter transmission in two raptor species during January and March 2006 at the Salton Sea, Imperial County, California. We captured 208 American Kestrels (Falco sparverius) (January, n=100; March, n=108) and 116 Burrowing Owls (Athene cunicularia) (January, n=52; March, n=64). Laboratory analysis revealed that 83% of American Kestrels and 31% of Burrowing Owls were positive for WNV-neutralizing antibodies. Additionally, two seroconversions were detected in Burrowing Owls between January and March. Infectious WNV, consistent with acute infection, was not detected in any bird.

Population Dynamics, Dispersal and Conservation of the ‘Canadian’ Burrowing OwlAthene cunicularia

Population Dynamics, Dispersal and Conservation of the ‘Canadian’ Burrowing Owl<i>Athene cunicularia</i>

Weather Conditions and Moon Phase Influence on Tropical Screech Owl and Burrowing Owl Detection by Playback in Southeast Brazil

Sampling owls in a reliable and standardized way is not easy given their nocturnal habits. Playback is a widely employed technique to survey owls. We assessed the influence of wind speed, temperature, air humidity, and moon phase on the response rate of the Tropical Screech Owl Megascops choliba and the Burrowing Owl Athene cunicularia in southeast Brazil. Tropical Screech Owl occurs in scrubland and wooded habitats, whereas the Burrowing Owl inhabits open grasslands to grassland savannah. Sixteen survey points were systematically distributed in four different landscape types, ranging from open grassland to woodland savannah. Field work was conducted in 2004 from June to December, the reproductive season of the two owl species. Our study design consisted of eight field expeditions of five nights each; four expeditions occurred under full moon and four under new moon conditions. At each survey station, we performed a broadcast/listening sequence involving several calls and vocalizations from each species, starting with Tropical Screech Owl (the smaller species). From 112 sample periods for each species within their respective preferred habitats, we obtained 54 responses from Tropical Screech Owl (48% response rate) and 30 responses (27% response rate) from Burrowing Owl. We found that the response rate of Tropical Screech Owl increased under conditions of higher temperature and air humidity, while the response rate of Burrowing Owl was higher during full moon nights.

Birds of Clarion Island, Revillagigedo Archipelago, Mexico

Abstract We recorded 62 bird species on Clarion Island, Mexico (Revillagigedo Archipelago, Pacific Ocean) during 1998–2006, eight of which breed there, 52 are considered non-breeders, and breeding is likely but unconfirmed for the Red-billed Tropicbird (Phaethon aethereus), Nazca Booby (Sula granti), and an unidentified shearwater. Thirty species are new for the island. A census of the Clarion Burrowing Owl (Athene cunicularia rostrata) in 2002/03 suggested a maximum total population of ∼850 pairs. At least 46 pairs of Laysan Albatrosses (Phoebastria immutabilis) bred in 2002/03, but the species experienced total breeding failure during our study. This result was unexpected because feral pigs (Sus scrofa) were successfully eradicated from Clarion by 2002; endemic Clarion Ravens (Corvus corax clarionensis), an endemic snake (Clarion Racer, Masticophis anthonyi), and an unidentified ant were associated with egg and hatchling failures. A small colony of an unidentified shearwater could be a recolonization by...