Burrowing Owl Research Articles

Responses of Female Burrowing Owls to Alterations in Clutch Size: Are Burrowing Owls Determinate or Indeterminate Egg-Layers?

Abstract Bird species, including raptors, can often be categorized into two groups depending upon their response to alterations in clutch size while laying. For some, clutch size is predetermined prior to the start of laying (i.e., determinate species). In contrast, the clutch size of indeterminate layers can be influenced by external factors present at the time of laying. Using field experiments, our objective was to examine the egg-laying responses of female Western Burrowing Owls (Athene cunicularia hypugaea) to manipulations of clutch size. To assess whether Burrowing Owls are determinate or indeterminate egg-layers, we altered female clutch size by removing or adding one egg during the laying period. At the time of egg removal or addition, the resident female had 1–5 of her own eggs present in her clutch. We compared the size of completed clutches of both removal and addition nests to the size of completed clutches at control nests. Mean clutch size at removal nests (x = 8.3 eggs, SE = 0.44, n = 9) ...

Nest site characteristics and reproductive success of burrowing owls (Strigiformes: Strigidae) in Durango, Mexico

The burrowing owl, Athene cunicularia, is a threatened red species in most of its North American distribution. Nest-site characteristics and reproductive success were compared for two breeding seasons in the southem Chihuahuan desert, Durango, Mexico. Reproductive success is highly correlated with the presence of the ProsopisHilaria grassland association. The following factors were not associated with nesting success: burrow type, distance to the nearest adjacent nest, soil texture and number of perches.

Differential risk perception of rural and urban Burrowing Owls exposed to humans and dogs

Urban areas expose wildlife to an array of novel predators, amongst which, humans and dogs are highly frequent. Thus, wild animals living in urban areas are forced to invest more time and energy in defence behaviours, which depend on how the risk is perceived and assessed. We experimentally tested whether Burrowing owls coming from rural and urban habitats showed differences in behavioural responses when facing humans and domestic dogs. We measured flight initiation distances (FIDs), nest returning, and aggressiveness level when owls faced a human and a human with a dog walking towards them. Our results showed that urban owls recognise a human with a dog as a greater threat than a human alone, thus indicating that fear of domestic animals should be considered as affecting owls' settlement in cities and towns. On the other hand, rural owls perceived human and dogs as similar threats, but showed higher FIDs, less aggressiveness, and lower tendency to return to the nest than urban owls in both treatments. These findings emphasize the importance of modified habitats in modelling the response of urban and rural owls to predators and represent another step in the explanation of how wild animals assess and respond to threats associated with living in urbanized environments.

Body Size and Sexual Dimorphism in the Southernmost Subspecies of the Burrowing Owl (Athene cunicularia cunicularia)

Abstract 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 ...

Rapid warming and drought negatively impact population size and reproductive dynamics of an avian predator in the arid southwest.

Avian communities of arid ecosystems may be particularly vulnerable to global climate change due to the magnitude of projected change for desert regions and the inherent challenges for species residing in resource limited ecosystems. How arid-zone birds will be affected by rapid increases in air temperature and increased drought frequency and severity is poorly understood because avian responses to climate change have primarily been studied in the relatively mesic northern temperate regions. We studied the effects of increasing air temperature and aridity on a Burrowing Owl (Athene cunicularia) population in the southwestern United States from 1998 to 2013. Over 16 years, the breeding population declined 98.1%, from 52 pairs to 1 pair, and nest success and fledgling output also declined significantly. These trends were strongly associated with the combined effects of decreased precipitation and increased air temperature. Arrival on the breeding grounds, pair formation, nest initiation, and hatch dates all showed significant delays ranging from 9.4 to 25.1 days over 9 years, which have negative effects on reproduction. Adult and juvenile body mass decreased significantly over time, with a loss of 7.9% mass in adult males and 10.9% mass in adult females over 16 years, and a loss of 20.0% mass in nestlings over 8 years. Taken together, these population and reproductive trends have serious implications for local population persistence. The southwestern United States has been identified as a climate change hotspot, with projections of warmer temperatures, less winter precipitation, and an increase in frequency and severity of extreme events including drought and heat waves. An increasingly warm and dry climate may contribute to this species' decline and may already be a driving force of their apparent decline in the desert southwest.

Detecting Burrowing Owl Bloodmeals in Pulex irritans (Siphonaptera: Pulicidae).

Pulex irritans L. is a cosmopolitan flea species that infests a wide variety of hosts. In North America it generally parasitizes large wild mammals, but in the Pacific Northwest an association has emerged between P. irritans and the western burrowing owl (Athene cunicularia hypugaea). While investigators have recognized this association for decades, it has not been clear if P. irritans feeds on burrowing owls, or if the owls serve exclusively as phoretic hosts. Here we describe using a real-time assay that was originally developed to identify bloodmeals in Ugandan cat fleas (Ctenocephalides felis Bouché) to detect burrowing owl DNA in P. irritans collected from burrowing owls in southern Idaho. Of 50 fleas tested, 12 had no detectable vertebrate bloodmeal. The remaining 38 (76%) contained burrowing owl DNA. The assay did not detect vertebrate DNA in unfed fleas exposed to owl or mouse pelts and is therefore unlikely to detect DNA in fleas from vertebrates that have served exclusively as phoretic hosts. We conclude that P. irritans feeds on burrowing owls. We discuss the potential implications of this finding for burrowing owl conservation and enzootic plague dynamics.

Bee in the nose: raptors let or let not stingless bees enter their nostrils

Relationships between birds and social insects include birds following ants, birds nesting close to active colonies of wasps or bees, and nesting inside termitaria. A little known relationship between birds and colonial insects is that of stingless bees (Meliponina) entering the nostrils of hawks and owls. Herein I report on a stingless bee entering the nostrils of the Roadside Hawk ( Rupornis magnirostris ), and on avoiding behaviours displayed by the same hawk species and a Burrowing Owl ( Athene cunicularia ) in presence of stingless bees hovering in front of their faces. The bees probably were seeking mucus inside the raptors’ nostrils, as already reported for a few birds of prey. Avoiding behaviour seems a novelty in this relationship between raptors and bees. The role stingless bees play in the lives of some bird species remains little known, and merits closer attention by field ornithologists and apidolologist.

Responses of birds to planting of Lotus tenuis pasture in the Flooding Pampas, Argentina

The Flooding Pampas is the most important livestock region of Argentina, but is a region where replacement of originally natural, perennial tussock grasses by pasture species is changing the heterogeneity of the grassland system. We evaluated the response of grassland bird assemblages of the Flooding Pampas to planting of Lotus tenuis (Lotus) pasture, which mainly modifies vegetation structure by reducing vertical heterogeneity. Species richness and abundance of birds were compared between fields of Lotus pasture and semi-natural grasslands. Avian species richness and abundance were both greater in semi-natural grassland than in Lotus pasture. When grouped by nesting habits (grassland specialists, generalists), species richness and abundance of grassland specialists was greater in semi-natural grassland, whereas richness and abundance of generalist species was greater in Lotus pasture. An indicator-species analysis showed that five grassland birds were closely linked to semi-natural grassland vegetation, with two of those species—Hudson's Canastero (Asthenes hudsoni) and Bay-capped Wren-Spinetail (Spartonoica maluroides)—of conservation concern.1 In contrast, generalist species, such as Southern Lapwings (Vanellus chilensis) and Burrowing Owls (Athene cunicularia), were associated with Lotus pasture. Planting of Lotus pasture has negative effects on species that naturally occur in tussock grassland. Grassland management methods, such as intercropping and rotational grazing, could help reconcile the effects of livestock production and the conservation grassland bird conservation in the Flooding Pampas.

Burrowing Owls, Pulex irritans, and Plague.

Western Burrowing Owls (Athene cunicularia hypugaea) are small, ground-dwelling owls of western North America that frequent prairie dog (Cynomys spp.) towns and other grasslands. Because they rely on rodent prey and occupy burrows once or concurrently inhabited by fossorial mammals, the owls often harbor fleas. We examined the potential role of fleas found on burrowing owls in plague dynamics by evaluating prevalence of Yersinia pestis in fleas collected from burrowing owls and in owl blood. During 2012-2013, fleas and blood were collected from burrowing owls in portions of five states with endemic plague-Idaho, Oregon, Washington, Colorado, and South Dakota. Fleas were enumerated, taxonomically identified, pooled by nest, and assayed for Y. pestis using culturing and molecular (PCR) approaches. Owl blood underwent serological analysis for plague antibodies and nested PCR for detection of Y. pestis. Of more than 4750 fleas collected from owls, Pulex irritans, a known plague vector in portions of its range, comprised more than 99.4%. However, diagnostic tests for Y. pestis of flea pools (culturing and PCR) and owl blood (PCR and serology) were negative. Thus, even though fleas were prevalent on burrowing owls and the potential for a relationship with burrowing owls as a phoretic host of infected fleas exists, we found no evidence of Y. pestis in sampled fleas or in owls that harbored them. We suggest that studies similar to those reported here during plague epizootics will be especially useful for confirming these results.

Extreme precipitation reduces reproductive output of an endangered raptor

Summary The frequency and intensity of extreme weather has increased in North America against a backdrop of anthropogenic land change. Few studies have examined how wildlife is affected by extreme weather, and none have examined whether any resulting effects are contingent upon the degree of anthropogenic landscape change. Using an 8‐year study in Canada (2003–2010), we examined how nest survival of burrowing owls Athene cunicularia varied in relation to weather, vegetation and soil type around the nest. Using a 3‐year (1992, 1993 and 1996) feeding experiment, we examined whether food limitation also causes owlet mortality during inclement weather. Lastly, we examined how productivity (i.e. annual fledgling output) between 2003 and 2010 varied as a function of breeding season precipitation anomalies. Using this relationship, we estimated how productivity has changed in response to breeding season precipitation anomalies from 1960 to 2012. During extreme precipitation events, nest survival decreased because of flooding. When burrow flooding did not occur, the youngest owlets in broods that were not food‐supplemented had the lowest survival rates when there was precipitation, yet almost all food‐supplemented owlets survived bouts of inclement weather. Accordingly, annual productivity from 2003 to 2010 varied inversely with breeding season precipitation anomalies, and we estimated that mean annual productivity decreased by 12% from 1960 to 2012. Synthesis and applications. Extreme rainfall during the breeding season reduced reproductive success of burrowing owls. Given that many raptors experience food limitation during extreme rainfall, large‐scale habitat management to increase the abundance and availability of prey may allow these species to better withstand acute food shortages. In light of predicted increases in the frequency and intensity of extreme weather, supplemental feeding could be used in triage situations for burrowing owl management and has the potential to be an effective short‐term conservation measure for other raptors. Protecting or reclaiming pastures in uplands that are less prone to flooding would further buffer burrowing owls and other ground‐nesting species from extreme precipitation. These actions should mitigate the negative effects of extreme rainfall in the short term; however, long‐term persistence of many species will become increasingly uncertain, as climate change scenarios predict an increase in the frequency and intensity of extreme weather.

First record of the Yellowish Pipit in Acre with notes on other grassland birds in southwestern Amazônia

This paper presents the first record of the Yellowish Pipit ( Anthus lutescens ) in the Brazilian state of Acre. This record represents the westernmost record of the species in Brazil and provides evidence of its expansion into the southwestern Amazon basin. We also present information on the occurrence of other bird species, typical of grasslands and other open habitats, e.g., the Burrowing Owl ( Athene cunicularia ), the White-tailed Hawk ( Geranoaetus albicaudatus ), the Southern Lapwing ( Vanellus chilensis ) and the Southern Caracara ( Caracara plancus ). These species have encroached southwestern Amazonia following environmental changes caused by human activities, such as the construction of highways and the conversion of the rainforest into cattle pasture. Keywords: Aves, Anthus lutescens , Motacillidae, open habitats, range extension.

Removal of old nest material decreases reuse of artificial burrows by burrowing owls

ABSTRACTArtificial burrows are considered an important management and conservation tool for burrowing owls (Athene cunicularia). This species regularly adorns natural and artificial burrows with mammal dung and other materials, which remain between years so that previous use of a nest site is often obvious. Moreover, ectoparasites (fleas) potentially overwinter in accumulated material and infest subsequent occupants. How evidence of prior use affects burrowing owl nest‐site decisions is not completely understood. We examined potential effects of the presence of old nest material on reuse of nests by burrowing owls in southwestern Idaho, USA, during 2004 and 2005. We manipulated artificial burrows that owls used for nesting in the prior year by; 1) removing material from the entrance, tunnel, and nesting chamber and replacing it with fresh soil; 2) microwaving old nest material to kill ectoparasites before returning it; or 3) removing and returning material without treatment to serve as a control. Relative to removal burrows, odds of burrowing owl reuse of ‘control’ and “microwave” burrows were 3.5 and 3.8 times greater, respectively. Removing ectoparasites by microwaving did not increase odds of reuse relative to control burrows, and fleas were present on nestlings in all 3 treatment groups. Presence of old material may help owls locate specific burrows when returning from migration or may provide physiological and feeding benefits. Thus, cleaning by removal of nest material from previously used artificial burrows may be counterproductive if maximizing reuse of nest sites by burrowing owls is a management objective. © 2015 The Wildlife Society.

Behavioural and morphological strategies by small savannah rodents to avoid predation

The study focused on vulnerability of small savannah mammals in relation to hearing, locomotion and activity on full moon nights in a continuum from more bushy to more open Cerrado physiognomies in order to understand predator selection in a southeast Brazilian savannah preserve. Diet preference of three nocturnal/crepuscular predators, a canid (maned wolf – Chrysocyon brachyurus) and two raptors (barn owl – Tyto alba and burrowing owl – Athene cunicularia), were assessed, simultaneously to measurement of rodent tympanic bulla volume, calculation of a prey bipedalism index (ratio between length of fore and hind limbs) and small mammal sampling in three different Cerrado physiognomies and on different moon phases. High bulla volume, low bipedalism index (bipedal locomotion) and high abundance/activity on darker nights and in bushy habitats are assumed as less vulnerability to predation. Although the Echymyidae Clyomys bishopi was the least vulnerable prey to aerial attack, possibly due to its good hearing (highest bulla volume), its predominantly quadrupedal locomotion (high bidepalism index) seemed not to be so efficient against the maned wolf, as it was preyed upon more than expected by chance by this canid. The Cricetidae Olygoryzomys nigripes and Calomys tener were either consumed opportunistically by the two owls or they were preyed upon at a frequency lower than expected by chance by the maned wolf. However, as the dominant species in the study area, C. tener was always consumed in large proportions. Olygoryzomys nigripes was the least vulnerable prey to the analysed predators, possibly due to its efficient locomotion (low bipedalism index) and scansorial habits, even though its bulla volume suggests a low hearing capability and the level of activity is the same during both lunar phases. As a vulnerable prey relative to hearing, locomotion and predominantly terrestrial habits, Calomys tener's strategy against predators is to decrease its activity on nights with a full moon and to inhabit physiognomies with more dense vegetation cover. The Cricetidae Necromys lasiurus seems to be especially vulnerable to the barn owl as it was consumed more than expected by chance. Its bulla relative volume was low, the bipedalism index and short tail indicate poor locomotion efficiency, and body size as well as terrestrial habits suit the barn owl's size and aerial hunting strategy. Mechanisms such as inflated bullae seem to play a secondary role in a more wooded environment, such as the savannah; locomotion mode, use of refuges and the exhibition of a more secretive behaviour (such as avoidance of moonlight) seem more effective in these neotropical landscapes.

Avian Use of Black-Tailed Prairie Dog Colonies in Shortgrass Prairie

Downward trends in populations of many grassland bird species are of conservation concern. Declines in black-tailed prairie dog ( Cynomys ludovicianus ) populations result in loss of habitat for birds and other species associated with their colonies. We measured abundance, diversity, and species composition of avian communities on prairie dog colonies and noncolony sites in the Texas Panhandle. More resident species ( P < 0.001) occurred on prairie dog colonies than on noncolony areas whereas, more nearctic-neoptropical migrants ( P = 0.003) and nearctic-temperate migrants ( P < 0.001) occurred on noncolony sites. Total avian abundance was greater ( P < 0.001) on noncolony sites than at prairie dog colonies, and differed by season ( P < 0.001). Barn swallows ( Hirundo rustica ), red-winged blackbirds ( Agelaius phoeniceus ), horned larks ( Eremophila alpestris ), and chipping sparrows ( Spizella passerina ) were more abundant on noncolony sites than on prairie dog colonies. Burrowing owl ( Athene cunicularia ), Cassin’s sparrow ( Peucaea cassinnii ), and lark bunting ( Calamospiza melanocorys ) abundances were greater on prairie dog colonies. Vegetative alterations made by prairie dogs may not influence bird populations as much in these shortgrass prairies as has been reported in mixed-grass prairies.

Distributional Changes in the Western Burrowing Owl (Athene cunicularia hypugaea) in North America from 1967 to 2008

The quantification of shifts in bird distributions in response to climate change provides an opportunity to gain a deeper understanding of the processes that influence species persistence. We used data from the North American Breeding Bird Survey (BBS) to document changes in the distributional limits of the western Burrowing Owl (Athene cunicularia hypugaea) from 1967 to 2008. We used logistic regression to model presence probability (p) as a function of longitude, latitude, and year. We modeled a linear trend in logit(p) through time with slope and intercept modeled as a double Fourier series of longitude and latitude. We found that the western Burrowing Owl has experienced an intriguing southward shift in the northern half of its breeding range, contrary to what is predicted by most species niche models and what has been observed for many other species in North America. The breeding range of the Burrowing Owl has been shrinking near its northern, western, and eastern edges. Our model detected the population declines that were observed in California and eastern Washington, in locations where maps based on route-specific estimating equations had predicted significant population increases. We suggest that the northern boundary of the breeding distribution of the western Burrowing Owl has contracted southward and the southern boundary of the species' breeding distribution has expanded southward into areas of northern Mexico that were formerly used only by wintering migrants.Cuantificar los cambios en las distribuciones de las aves en respuesta al cambio climático proporciona una oportunidad para obtener una comprensión más profunda de los procesos que influyen en la persistencia de las especies. Utilizamos datos del Censo de Aves Reproductoras de América del Norte (BBS en inglés) para documentar los cambios en los límites de distribución de Athene cunicularia hypugaea desde 1967 a 2008. Utilizamos una regresión logística para modelizar la probabilidad de presencia (p) como una función de la longitud, la latitud y el año. Modelizamos una tendencia lineal para el logit de (p) a lo largo del tiempo con pendiente y ordenada en el origen introducidos como una serie doble de Fourier de longitud y latitud. Encontramos que A. c. hypugaea ha experimentado un curioso desplazamiento hacia el sur en la mitad norte de su área de reproducción, al contrario de lo que predicen la mayoría de los modelos de nicho específicos y de lo que se ha observado en muchas otras especies en América del Norte. El área de cría de A. c. hypugaea ha ido contrayéndose en sus extremos norte, oeste y este. Nuestro modelo detectó el declive poblacional observado en California y en el este de Washington, donde los mapas basados en las ecuaciones de estimación de rutas específicas habían predicho aumentos significativos de la población. Sugerimos que el límite norte de la distribución del área de cría de A. c. hypugaea se ha contraído hacia el sur y el límite sur de la distribución del área de cría de la especie se ha expandido hacia el sur en zonas del norte de México que antes eran utilizadas sólo por migrantes invernales.

Estructuras artificiales para la anidación y su relación con el éxito reproductivo del gavilán pescador y del tecolote llanero durante ocho temporadas reproductivas en el estero La Pinta, Puerto Peñasco, Sonora, México

La reproducción en aves puede estar limitada por la ausencia de sitios de anidación. En el estero La Pinta, Puerto Peñasco, Sonora, no existían registros de reproducción del gavilán pescador (Pandion haliaetus) ni del tecolote llanero (Athene cunicularia). Construimos siete nidos artificiales con cuatro estructuras metálicas en forma de sahuaro para el gavilán pescador y tres cajones de concreto de 60x60x60 cm para el tecolote; esto con el fin de promover su reproducción. Durante ocho temporadas, entre 2006 y 2013, realizamos observaciones desde puntos a 100 m de las estructuras artificiales. El gavilán pescador anidó en al menos una estructura artificial en siete de las ocho temporadas. Durante el estudio registramos 17 nidos con 55 huevos, de los cuales 53 llegaron a volantones en sahuaros artificiales y postes de tendido eléctrico. Una pareja de tecolote llanero anidó en 2006 en una estructura artificial con una nidada de seis huevos, y otra lo hizo en una oquedad natural con una nidada de siete huevos; cinco y seis pollos eclosionaron, respectivamente. Durante las cinco temporadas siguientes estuvieron ausentes en el área; regresaron en 2012 y registramos una pareja con cuatro huevos, todos eclosionaron. En 2013, observamos cinco parejas de tecolotes, cuatro anidando en oquedades naturales y una en una estructura artificial; tuvieron una nidada total de 24 huevos: eclosionaron 19 pollos. El promedio de huevos por pareja fue de 4.8 para esta especie. Las alternativas de los gavilanes pescadores para anidar en el área de estudio fueron los postes de tendido eléctrico y los sahuaros artificiales; en este estudio, anidaron preferentemente en los sahuaros artificiales. Los tecolotes llaneros tuvieron como alternativas las oquedades naturales y las artificiales; cinco de las ocho parejas registradas seleccionaron las naturales.

Spatial patterns in hydrogen isotope ratios in feathers of Burrowing Owls from western North America

ABSTRACT Deuterium (2H) has been used to track movements of land birds, under the assumption that δ2H in precipitation (δ2Hp) and δ2H in bird feathers (δ2Hf) are correlated across broad geographic gradients. The nature of this correlation has been evaluated only in a small percentage of the birds that breed in North America. We sampled Western Burrowing Owl (Athene cunicularia hypugaea) feathers of known origin (nestling feathers) at 36 locations throughout North America (from southern Canada to central Mexico). We used a modification of the “comparative equilibrium” technique of Wassenaar and Hobson (2003) to measure the δ2H of nonexchangeable hydrogen in feather samples. We characterized the strength of the relationship between δ2Hf and amount-weighted mean annual δ2Hp in a raptor that breeds in arid grasslands and deserts throughout western North America. We used a Bayesian hierarchical approach to model the δ2Hf–δ2Hp relationship, accounting for levels of intrinsic and extrinsic variation in δ2Hf. We ...

Burrowing Owl (Athene cunicularia) Habitat Associations in Agriculture Fields and along Canal Trails in Phoenix, Arizona

Burrowing Owls (Athene cunicularia) have experienced significant population declines over the last 100 years in parts of the United States and Canada. This decline may be associated with increasing urbanization and land-cover change; however, owls can occupy urbanized environments. To determine habitat selection in the southeast valley of Phoenix, Arizona, we conducted visual surveys for owls during summer 2011 and measured microhabitat and landscape characteristics in 23 agricultural fields (fields) and along 15 canal right-of-ways (trails). We estimated occupancy rate and detectability using Program MARK. We identified microhabitat selection to relate owl occurrence to landscape variables. Occupancy rate was 32% in both fields and trails and owls had greater detectability along trails. Burrowing Owl occurrence was similar in fields with varying agricultural stages (from undisturbed to harvested) and moisture conditions. Owl occupancy was positively associated with soil type and canal water presence, and occupancy decreased when developed landscape cover (e.g., roads and buildings) increased. These findings suggest that Burrowing Owls are able to live in urbanized environments below 40% developed land cover provided that water and suitable soils are available.

Apparent survival of adult Burrowing Owls that breed in Canada is influenced by weather during migration and on their wintering grounds

Understanding factors that influence the survival of endangered migratory species is critical for making informed management decisions, yet this understanding relies on long-term recapture datasets for species that are, by definition, rare. Using 3 geographically widespread (Saskatchewan, Alberta, and Manitoba, Canada) and long-term (6–15 yr) mark–recapture datasets, we quantified spatial and temporal variation in apparent annual survival and recapture probabilities of Burrowing Owl (Athene cunicularia), an endangered species that breeds in Canada. We then examined how large-scale weather patterns during migration (storms) and on the wintering and breeding grounds (precipitation), in addition to prey irruptions on the breeding grounds, influenced apparent survival of Burrowing Owls. Female Burrowing Owls had lower apparent survival than males in all 3 study areas. Storms during fall migration and above-average precipitation on the wintering grounds were associated with reduced apparent survival of Burrowing Owls in the longest-running study area, Saskatchewan; in Alberta and Manitoba, there were few correlations between apparent survival of Burrowing Owls and weather or prey irruptions. Increases in stochastic events such as storms during migration or precipitation on the wintering grounds could have adverse consequences on the already small Burrowing Owl population in Canada. Local management actions that focus solely on improving adult apparent survival within Canada are likely insufficient for mitigating susceptibility of adults to inclement weather or other factors outside the breeding season, underscoring the need for management of this species across multiple jurisdictions within North America.

Response of burrowing owls to experimental removal of satellite burrows

Studies of habitat relationships indicate that burrowing owls (Athene cunicularia) often select nest sites with multiple burrows. This behavior may increase survival of post-emergent nestlings. We experimentally blocked access to burrows within 20m of nests (satellite burrows) within a large grassland in central California to evaluate the response by year-round resident burrowing owls to removal of satellite burrows. We compared reproductive performance and nest fidelity between owls whose access to potential satellite burrows was blocked and owls whose nests had similar numbers of naturally occurring burrows within 20m of the nest prior to manipulation. Adult owls and their young moved away from treatment nests, but reproductive rates between owls from treatment and control nests did not differ. Movements involved the entire family, occurred before young had fledged, and owls did not return to the natal nest burrow. Movements ranged from 25m to 120m and occurred at 5 of the 7 treatment nests with young. No such movement occurred at any of the control nests. Our findings support results from correlational studies that multiple nearby burrows influence nest site selection. 2014 The Wildlife Society