Multiscale Habitat Selection by Burrowing Owls in Black-Tailed Prairie Dog Colonies

ABSTRACT Some populations of western burrowing owls (Athene cunicularia hypugaea) have declined in recent decades. To design and implement effective recovery efforts, we need a better understanding of how distribution and demographic traits are influenced by habitat quality. To this end, we measured spatial patterns of burrowing owl breeding habitat selection within black-tailed prairie dog (Cynomys ludovicianus) colonies in northeastern Wyoming, USA. We compared burrow-, site-, colony-, and landscape-scale habitat parameters between burrowing owl nest burrows (n = 105) and unoccupied burrows (n = 85). We sampled 4 types of prairie dog colonies: 1) owl-occupied, active with prairie dogs (n = 16); 2) owl-occupied, inactive (n = 13); 3) owl-unoccupied, active (n = 14); and 4) owl-unoccupied, inactive (n = 14). We used an information-theoretic approach to examine a set of candidate models of burrowing owl nest-site selection. The model with the most support included variables at all 4 spatial scales, and results were consistent among the 4 types of prairie dog colonies. Nest burrows had longer tunnels, more available burrows within 30 m, and less shrub cover within 30 m, more prairie dog activity within 100 m, and were closer to water than unoccupied burrows. The model correctly classified 76% of cases, all model coefficients were stable, and the model had high predictive ability. Based on our results, we recommend actions to ensure persistence of the remaining prairie dog colonies as an important management strategy for burrowing owl conservation in the Great Plains of North America.     

The importance of visual cues for nocturnal species: eagle owls signal by badge brightness

Nocturnal species may communicate by visual signals more frequentlythan previously thought. In fact, such species are habituallyactive around sunset and sunrise, when light conditions arestill suitable for visual communication. We investigated thecommunication function of a visual cue in the eagle owl Bubobubo, a nocturnal predator. In this species, territorial andcourtship displays peak during the sunset and sunrise periodsand involve the display of a white badge located on the throatwhose reflectance properties are sex and period dependent. Experimentalintrusions were conducted at 30 eagle owl territories in orderto understand the function of the white badge during contests.We analyzed the reactions of both male and female owners towarda taxidermic mount with a normal brightness and a brightness-reducedwhite badge, with both male and female territorial calls. Ourresults indicate that the white badge of eagle owls plays animportant role in visual communication during contests. Malesdisplayed more frequently toward male low-brightness mounts,which were also approached more closely or attacked. Femalebehavior did not differ between experimental groups. Furthermore,a positive relationship between male badge brightness and breedingoutput suggested a potential role of the white badge as an honestsignal of male quality. The need to convey information by visualcommunication in a nocturnal species may have promoted the evolutionof visual signals employed at crepuscule.     

Review of the effects of barred owls on spotted owls

Barred owls (Strix varia) are forest-dwelling owls, native to eastern North America, with populations that expanded westward into the range of the spotted owl (Strix occidentalis). Barred owls exert an overwhelmingly negative influence on spotted owls, thereby threatening spotted owl population viability where the species co-occur. In this review, we provide an overview of the barred owl's range expansion and detail and synthesize previously published literature on spotted and barred owls within the range of the spotted owl as related to potential future outcomes for the northern spotted owl (S. o. caurina). We include research on diet, habitat use and selection, effects of barred owls on spotted owl demography and behavior, hybridization with spotted owls, parasites, contemporary management, and future research needs for spotted owl populations given continued barred owl expansion throughout western North America. Our literature review and synthesis should provide managers with the information necessary to develop strategies that mitigate deleterious effects of barred owls at local and landscape scales. © 2019 The Wildlife Society.     

Urban to forest gradients: Suitability for hollow bearing trees and implications for obligate hollow nesters

Resource availability is a limiting factor influencing the distribution and composition of faunal communities. Globally, hollow bearing trees are a resource required by wildlife at all trophic levels, and are used for a diverse range of ecological functions. In the northern hemisphere avian species act as primary hollow excavators, whereas the southern hemisphere must rely on complex interactions between stochastic events, and eventual decay. Hollow formation is therefore a slow process in the southern hemisphere. In contrast, hollow loss is quite rapid and influenced greatly by anthropogenic impacts. To identify the ecological characteristics driving hollows over an urban to forest gradient as a resource for the powerful owl (Ninox strenua) and its prey we used presence‐only modelling. The potential for an area to support tree hollows suitable for powerful owls and their prey was linked to the density of ephemeral rivers, land cover, tree cover and distance from riparian vegetation. The potential for large hollows throughout the landscape, suitable for the powerful owl, was also influenced by density of permanent rivers. Potential habitat for tree hollows, capable of supporting powerful owls and their prey was greatest in forested environments, declining with increased urbanization. However the urban region still supported some smaller tree hollows suitable for arboreal marsupials. Managing for urban dwelling species, is not as simple as retaining old hollow producing trees or providing alternate nesting structures. We also need to mitigate increased mortality associated with built environments (e.g. electrocution, collisions).     

Surgical bone marrow aspiration in Aotus lemurinus griseimembra

Aotus lemurinus griseimembra are highly susceptible to infection by human malaria parasites and reproduce some of its clinical manifestations, including anemia. We developed a new surgical technique to obtain bone marrow samples from Aotus by surgical aspiration of the femur. First, we determined that the femur offered advantages over other bones, primarily due to lower fracture vulnerability. We tested a surgical technique using 20 G IV catheters in formaldehyde-preserved animals, then conducted the procedure on 27 live animals. This technique provided easy, quick surgical access to adequate volumes of bone marrow and was safe for almost all animals: only one died; another developed nervous impairment of the lower limb. Adequate cell samples were obtained in all animals and allowed cytological studies. This procedure offers a useful tool for bone marrow research in Aotus and helps overcome current limitations of such research in human where these studies are limited by ethical and technical issues.     

Thermoregulatory use of heat increment of feeding in the tawny owl (Strix aluco)

The heat increment of feeding (HIF) was investigated in the tawny owl (Strix aluco) in central Norway (63°N, 10°E), close to the northern limit of its distribution. HIF was measured as the increase in heat production (measured as oxygen consumption) after force-feeding the owls with laboratory mice at thermoneutral conditions (20 °C) and during cold-exposure (5 °C and −5 °C). The basal metabolic rate of the owls (mean mass 419 g) was 4.39 kJ h⁻¹ and the lower critical temperature was approximately 16 °C. During cold conditions, HIF substituted for thermogenesis, and at an ambient temperature of −5 °C the substitution was complete. Calculations indicate that the substitution by HIF may save the owls as much as 60% of their daily thermoregulatory costs. This corresponds to about 10% of their total daily energy budget.     

Isolation and characterization of 21 microsatellite markers in the barn owl (Tyto alba)

We report 21 new polymorphic microsatellite markers in the European barn owl (Tyto alba). The polymorphism of the reported markers was evaluated in a population situated in western Switzerland and in another from Tenerife, Canary Islands. The number of alleles per locus varies between two and 31, and expected heterozygosity per population ranges from 0.16 to 0.95. All loci are in Hardy-Weinberg equilibrium and no linkage disequilibrium was detected. Two loci exhibit a null allele in the Tenerife population.