Burrowing Owl Research Articles

Animal behaviour: use of dung as a tool by burrowing owls.

Reports of tool usage by birds tend to be anecdotal as only a few individuals may be involved and the behaviour observed can often be interpreted in other ways. Here we describe the widespread collection of mammalian dung by burrowing owls (Athene cunicularia) and show that they use this dung as a bait to attract dung beetles, a major item of prey. Our controlled investigation provides an unambiguous estimate of the importance of tool use in a wild animal.

Burrowing owls and burrowing mammals: are ecosystem engineers interchangeable as facilitators?

Terrestrial vertebrates exhibit dynamic, positive interactions that form and dissolve under different circumstances, usually with multiple species as participants. Ecosystem engineers are important facilitators of other species because they cause physical changes in the environment that alter resource availability. Although a species can be associated with more than one partner, facilitators may not be interchangeable if they differ in abundance, behavioral characteristics, or interactions with other factors in ways that condition the outcome of the association. We examined interactions between burrowing owls (Athene cunicularia) and two burrowing mammals, hairy armadillos (Chaetophractus villosus) and plains vizcachas (Lagostomus maximus), and determined whether these ecosystem engineers are interchangeable for owls. We examined reproductive success for owls nesting in these mammal burrows, constructed a logistic regression model to identify habitat characteristics associated with owl nests, and examined the engineering activities of the mammals. Data on reproduction and habitat indicate that armadillos and vizcachas are not interchangeable for owls. Thirty‐five percent of the nests in vizcacha burrows produced fledglings; no fledglings were produced from nests outside vizcachas colonies, even though owls nest successfully in armadillo burrows in other parts of Argentina. Vizcachas facilitate burrowing owls by construction of burrows and by producing open understory vegetation through herbivory. In contrast, armadillos do not alter vegetation, and their burrows are suitable for nest sites only when they occur in recently burned areas or areas maintained by anthropogenic disturbance. Our habitat model also suggests that fire plays a key role in maintaining owl populations because fire is the only natural process that reduces shrubs to the level required by owls. Current management practices of eradication of vizcachas and fire suppression in shrublands could have strong negative consequences for burrowing owls.

Territory defense of nesting Burrowing Owls: responses to simulated conspecific intrusion

To investigate the potential expression of territorial behavior of Burrowing Owls (Athene cunicularia) in southwestern Idaho, we used a playback protocol to determine if Burrowing Owls actively defended their nesting site from conspecifics, and if so, to determine the extent of their territorial boundaries. Eighty-eight percent of male Burrowing Owls responded to the broadcast of conspecific primary calls. All responsive males uttered primary calls, and many owls approached the broadcast speaker, exhibited white-and-tall stances, and bobbed. Females responded less frequently than males, but one female whose mate was presumably dead exhibited an intense response to the playback trial. There were no differences in number of primary calls uttered, number of white-and-tall stances performed, or number of bobs of focal males among three broadcast distances: (0 m, 50 m, and 100 m) from the active nest burrows. However, focal owls approached the broadcast speaker more closely at broadcast distances of 0 m and 50 m than at 100 m. These findings suggest that owls actively defended their nesting site from conspecifics and that they defended an area larger than that immediately surrounding the nest burrow. Although they continued to vocalize at distances of at least 100 m, they did not physically approach an intruder at this distance as frequently as at shorter distances. Therefore, Burrowing Owls appear to defend a territory that encompasses some, but not all, of the foraging area used during nesting.

Grassland bird densities in seral stages of mixed-grass prairie

Birds associated with prairie ecosystems are declining and the ecological condition (seral stage) of remaining grassland communities may be a factor. Livestock grazing intensity influences the seral stage of grassland communities and resource managers lack information to assess how grassland birds are affected by these changes. We estimated bird density, species diversity, and species richness on 37 sites in 4 seral stages of western wheatgrass [Pascopyrum smithii (Rydb.) A. Löve]-green needlegrass [Nassella viridula (Trin.) Barkworth] communities of the Fort Pierre National Grassland. Bird species richness did not differ among seral stages (P = 0.57), but bird species diversity was greater (P < 0.10) in early seral stages compared to late-intermediate seral stages. Grasshopper sparrow (Ammodramus savannarum Gmlin), bobolink (Dolichonyx oryzivorus Linnaeus), dickcissel (Spiza americana Gmlin), and brown-headed cowbird (Molothrus ater Boddaert) density increased (P < 0.10) from early to late seral stages. Burrowing owl (Athene cunicularia Molina), upland sandpiper (Bartramia longicauda Bechstein), chestnut-collared longspur (Calcarius ornatus Townsend), and horned lark (Eremophila alpestris Linnaeus) density decreased (P < 0.10) from early to late seral stages. Western meadowlarks (Sturnella neglecta Audubon) were more abundant in early (P = 0.05) and early-intermediate (P = 0.01) seral stages than late seral stages. Birds with habitat requirements including tall vegetation and residual cover were more abundant in later seral stages. Early seral stages were beneficial to birds that prefer short grass and sparse vegetative cover. Seral stage was an effective predictor of density for many bird species. A mosaic that includes all seral stages is necessary to maximize grassland bird species diversity and abundance across the landscape. Managers can assess the effects on grassland birds of management actions that alter the seral stage of the vegetation.

Nest stage, wind speed, and air temperature affect the nest defence behaviours of burrowing owls

The effect of nest stage on nest defence responses has been fairly well established but the impact of weather conditions has been largely ignored. We examined the effects of nest stage, number of previous visits, wind speed, and air temperature on burrowing owl (Athene cunicularia (Molina, 1782)) defence of nests from a human intruder. We found that burrowing owls changed nest defence tactics from retreat behaviour to more confrontational behaviour once eggs hatched. Aggressiveness was significantly reduced as wind velocity increased and when temperatures were warmer. We found no evidence for a change in owl defence behaviour with the number of previous visits to a nest. Although not statistically significant, there was a tendency for burrowing owls to allow closer approaches and to not retreat as far once eggs had hatched. Wind speed did not have an effect on retreat or approach distances, and owls allowed us to get significantly closer to the nest before retreating when air temperatures were warm. There are a multitude of factors that could affect nesting success and thus fitness of birds, but our study shows that routine climatic events such as warm weather had a measurable impact on how a bird defended its reproductive investment.

Effectiveness of voluntary habitat stewardship in conserving grassland: case of operation burrowing owl in Saskatchewan.

There have been no published performance evaluations of nongovernmental, voluntary habitat stewardship programs. The Operation Burrowing Owl (OBO) stewardship program, initiated in 1987, was evaluated for its effectiveness in conservation of grassland habitat during 1986-1993. The 108 OBO sites from 1987 to 88 and 98 randomly selected non-OBO sites that were grassland in 1986 in the Regina-Weyburn, Saskatchewan study area were classified by size and agricultural soil suitability. By 1993, 41 (38%) of the 108 OBO sites had been withdrawn from the program. The 1986 area of grassland was compared with grassland area calculated from digitized 1993 LANDSAT imagery. A correction for satellite inaccuracies was determined. Grassland retention in 1993 was significantly higher at OBO sites (66%) than at random sites (49%), demonstrating that the OBO voluntary program effectively conserved habitat. Also, grassland retention was significantly lower on sites with better agricultural soils, and for sites <12 ha in size. Site type (OBO or random), size and their interaction, followed by agricultural soil suitability, had the greatest effects on grassland retention. During an era of accelerated grassland loss, OBO strongly and positively (statistically significant) affected conservation of grassland sites most at risk: sites <12 ha in size and with good to excellent agricultural soils. This suggests that grassland conservation efforts focus on vulnerable sites (small size and/or good agricultural soils) to provide nesting habitat for burrowing owls. Our study demonstrates that a voluntary stewardship program can significantly increase conservation of habitat.

Grassland bird densities in seral stages of mixed-grass prairie

Birds associated with prairie ecosystems are declining and the ecological condition (seral stage) of remaining grassland communities may be a factor. Livestock grazing intensity influences the seral stage of grassland communities and resource managers lack information to assess how grassland birds are affected by these changes. We estimated bird density, species diversity, and species richness on 37 sites in 4 seral stages of western wheatgrass [Pascopyrum smithii (Rydb.) A. Löve]-green needlegrass [Nassella viridula (Trin.) Barkworth] communities of the Fort Pierre National Grassland. Bird species richness did not differ among seral stages (P = 0.57), but bird species diversity was greater (P &lt; 0.10) in early seral stages compared to late-intermediate seral stages. Grasshopper sparrow (Ammodramus savannarum Gmlin), bobolink (Dolichonyx oryzivorus Linnaeus), dickcissel (Spiza americana Gmlin), and brown-headed cowbird (Molothrus ater Boddaert) density increased (P &lt; 0.10) from early to late seral stages. Burrowing owl (Athene cunicularia Molina), upland sandpiper (Bartramia longicauda Bechstein), chestnut-collared longspur (Calcarius ornatus Townsend), and horned lark (Eremophila alpestris Linnaeus) density decreased (P &lt; 0.10) from early to late seral stages. Western meadowlarks (Sturnella neglecta Audubon) were more abundant in early (P = 0.05) and early-intermediate (P = 0.01) seral stages than late seral stages. Birds with habitat requirements including tall vegetation and residual cover were more abundant in later seral stages. Early seral stages were beneficial to birds that prefer short grass and sparse vegetative cover. Seral stage was an effective predictor of density for many bird species. A mosaic that includes all seral stages is necessary to maximize grassland bird species diversity and abundance across the landscape. Managers can assess the effects on grassland birds of management actions that alter the seral stage of the vegetation.

Black-tailed prairie dogs and the structure of avian communities on the shortgrass plains.

We tested the hypothesis that black-tailed prairie dogs (Cynomys ludovicianus) influence avian community structure on the shortgrass prairie. We surveyed 36 prairie dog towns and 36 paired sites without prairie dogs during summer and fall of 1997, 1998, and 1999 in the Oklahoma Panhandle. Our surveys totaled 9,040 individual observations for 73 avian species. Significantly distinct avian communities were present on prairie dog towns when compared to sites within four different macrohabitats of the surrounding landscape: open rangeland, scrub/sandsage (Artemisia filifolia) habitats, Conservation Reserve Program (CRP) plots, and fallow crop fields. Relative densities of all bird species combined was higher on prairie dog towns versus paired sites in summer and fall. Mean species richness of birds was significantly higher on prairie dog towns than paired sites during summer, but there were no significant differences in fall. Open rangeland had the highest mean species richness in fall. Assemblages of avian communities differed significantly between prairie dog towns and the four macrohabitat types during summer. Burrowing owls (Athene cunicularia), killdeer (Charadrius vociferous), horned larks (Eremophila alpestris), and meadowlarks (Sturnella spp.) were positively and significantly associated with prairie dog towns during summer, while horned larks and ferruginous hawks (Buteo regalis) were significantly associated with prairie dog towns during fall. Even in their current remnant state, black-tailed prairie dogs continue to play a significant role in the assembly of ecological communities across the Great Plains. Conservation of prairie dogs goes well beyond a single species, and is an important strategy for the preservation of the prairie ecosystem as a whole.

Factors Related to Body Condition of Nestling Burrowing Owls in Buffalo Gap National Grassland, South Dakota

We analyzed the body condition of nestling Burrowing Owls (Athene cunicularia) at Buffalo Gap National Grassland during the summers of 1999 and 2000. In 1999, which had a wet spring, body condition was negatively related to brood size and distance from nest to colony edge. There was no relationship between body condition and brood size during 2000, which had normal precipitation. In 2000, nestlings of early arriving pairs were in better body condition than those that arrived later. The variance in body condition within a brood was not related to brood size.

Estimation of Reproductive Rates of Burrowing Owls

Obtaining reliable estimates of absolute and relative reproductive rates is challenging for avian species whose nests are difficult to observe, such as the burrowing owl (Athene cunicularia). We compared methods for estimating reproductive rates of burrowing owls, defined as the number of 21- to 28-day-old young per successful nest. We compared observations using (1) the mean and (2) the maximum number of young observed during 5 30-min observation periods, and (3) the maximum number of young videotaped during 2-hr video surveillance. We evaluated the reliability of these methods with the known number of young present in nest boxes. All 3 methods performed poorly as estimators of absolute reproductive rates (absolute bias >23%, root mean square error [RMSE] >42%). Video surveillance performed most poorly of the 3, with a high incidence of failing to detect any young at successful nests. The maximum number of young observed from direct nest observations was correlated with the known number of young (r=0.82 ± 0.13, n = 21) and provided more reliable estimates of relative than absolute reproductive rates. The mean number of young observed from direct observations was correlated with the known number of young (r = 0.64 ± 0.18, n = 21), but had both higher bias and lower precision than the maximum number observed for estimation of relative reproductive rates. Our results suggest that using counts of young observed outside of the nest burrow may lead to incorrect conclusions on factors affecting reproductive rates. When counts are the basis of inference, the effort researchers use at each nest should be standardized and reported. Further work on field methods that allow estimation of detection probability, or ensuring that all young are observed, will be imperative in providing reliable estimates.

Post-Fledging Survival of Burrowing Owls in Saskatchewan

Extensive research into the decline of the endangered burrowing owl (Athene cunicularia) has focused on breeding biology, but has largely ignored the post-fledging period. To determine whether post-fledging survival was an important factor in the decline we used radiotelemetry to monitor post-fledging juveniles in a migratory population of burrowing owls in southern Saskatchewan, Canada, during 1997-2000. As part of a concurrent study, 92% of the owl pairs nested in artificial nest boxes, and 64% received supplemental food from hatch until fledging. Survival of juvenile owls during the 3-month, post-fledging period was significantly higher in 1997 (1.00, n = 12) than 1998-2000 (0.55 [95% CI: 0.44 to 0.70], n = 64; P = 0.02). Unusually high survival during 1997 may have been related to the unusually high abundance of voles (Microtus spp.) that year. From 1998 to 2000, 27 of 64 radiomarked owls died. Predators caused the majority of post-fledging mortality (15 of 27), with juveniles at greatest risk the first 14 days after fledging. Other sources of mortality were related to anthropogenic factors (5 of 27) and starvation (5 of 27). Following each of 3 years with moderate juvenile post-fledging survival, the breeding population of burrowing owls declined 11-48% and contained correspondingly few yearling recruits (x = 2.1%). However, following the year of high post-fledging survival (1997), the breeding population increased by 32%, and yearling recruitment was substantially higher (8.3%). These results suggest that post-fledging survival has a considerable influence on population size in the subsequen breeding season, and that management strategies for this species of concern should include this life stage.

Comparison of Detection Probability Associated with Burrowing Owl Survey Methods

Populations of western burrowing owls (Athene cunicularia hypugaea) appear to have declined in many portions of their range. A standardized survey and monitoring program is not available to quantify changes in abundance or distribution. Before a standardized survey method is selected for long-term, continent-wide burrowing owl monitoring, potential survey protocols should be rigorously tested. We evaluated 3 potential burrowing owl survey methods: line transect, roadside point-count, and driving surveys. We also examined the effectiveness of using call-broadcasts on point-count surveys to increase detection probability. We conducted 3 replicate borrowing owl surveys (either point-count or driving surveys) along 1,350 km of roads (114 survey routes) in eastern Wyoming, USA, between June and August 2000. Detection probability varied among observers for both point-count and driving surveys. Detection probability was higher on point-count, surveys (x = 64.3%) compared to driving surveys (x = 37.5%), and point-count surveys sampled a larger effective area away from the road. Walking line-transect surveys proved ineffective and inefficient for monitoring burrowing owls at large (statewide) scales. Nest-site detection probability was 47% during driving detection trials and 79% during point-count detection trials. We detected over twice as manly owls per unit distance on our point-count routes (0.038 owls/km) compared to our driving routes (0.016 owls/km), but detected more owls per unit time on our driving routes (0.339 owls/hr vs. 0.229 owls/hr on point-count routes). We detected 22% more owls using call-broadcast even though all of our detections on pointcount surveys were visual rather that aural. Estimates of breeding density were fairly similar based on our driving and point-count surveys (0.110 and 0.074 nest sites/km 2 , respectively). Standardized point-counts using call-broadcast along roadsides offer the best approach for monitoring population trends of burrowing owls at large (statewide) spatial scales. Based on our results, we developed a standardized survey protocol for monitoring burrowing owls at large spatial scales. Implementation of these monitoring protocols would provide more precise estimates of population trends of burrowing owls in North America.

Space Use and Pesticide Exposure Risk of Male Burrowing Owls in an Agricultural Landscape

We estimated home-range size and habitat selection in a population of burrowing owls (Athene cunicularia) living within an agricultural landscape in the Central Valley of California, USA, in 1998 and 1999. We modeled home-range size and habitat selection of breeding male owls (n = 33) as a function of biological and physical factors. Biological factors included number of young fledged and diet, and physical factors included cover-type composition around the nest. We also examined patterns of space use in conjunction with agricultural pesticide application records for evidence of secondary poisoning risk to the owls. Owl home ranges varied in size within (but not between) years, and not in conjunction with any of the biological factors we measured. Foraging versus random locations were differentiated most strongly by distance from the nest, with 80% of nocturnal foraging observations falling within 600 m of the nest burrow. No single cover type was selected when distance to nest was also included in the model. Owls did use agricultural fields recently treated with pesticides, although we did not find evidence of owls selectively foraging in these fields.

Isolation and characterization of microsatellite DNA primers in burrowing owl (Athene cunicularia)

AbstractWe developed polymerase chain reaction (PCR) primers to amplify 22 microsatellite DNA loci in burrowing owls (Strigiformes: Athene cunicularia). The seven most easily amplified and scored polymorphic loci are presented. These show 3−19 alleles per locus and expected heterozygosities of 0.067–0.712. Inheritance at all loci conformed to Mendelian expectations among six owl families, and six loci conform to Hardy–Weinberg expectations.

Large clutch size of a Burrowing Owl, Athene cunicularia, found in Saskatchewan

Large clutch size of a Burrowing Owl, Athene cunicularia, found in Saskatchewan

CONSERVATION OF GRASSLAND BIRDS IN AN URBANIZING LANDSCAPE: A HISTORICAL PERSPECTIVE

Abstract Landscape alterations resulting from urban expansion are among those factors negatively impacting Great Plains grassland birds. The City and County of Boulder, Colorado, manage one of the largest grassland open-space systems in North America, but it is embedded in an area of rapid urban growth. We compared bird count data from the 1980s and 1990s with checklist information about the Boulder grassland avifauna between 1900 and 1937, with the goal of determining what proportion and which species of the historical grassland avifauna are being sustained on Boulder open space. Of 29 native species present in 1900, 22 (76%) appeared on our counts in the 1990s. Formerly common species that disappeared or declined mostly were birds associated with shortgrass prairie, including Burrowing Owl (Athene cunicularia), Common Nighthawk (Chordeiles minor), Loggerhead Shrike (Lanius ludovicianus), and Lark Bunting (Calamospiza melanocorys). By contrast, species associated with mixed and tallgrass habitats increas...

The rattling sound of rattlesnakes (Crotalus viridis) as a communicative resource for ground squirrels (Spermophilus beecheyi) and burrowing owls (Athene cunicularia).

The rattling sound of rattlesnakes (Crotalus viridis) as a communicative resource for ground squirrels (Spermophilus beecheyi) and burrowing owls (Athene cunicularia).

A modified protocol for sex identification of in ovo avian embryos and its application as a management tool for endangered species conservation programs.

A simple, reliable, and safe protocol was developed for the collection of small amounts of blood from avian eggs of variable size and at early stages of development. Fifty eggs were used in the study; 40 were common chicken (Gallus domesticus) eggs, six were homing pigeon (Columba livia domestica) eggs, and four were burrowing owl (Athene cunicularia) eggs. Collection was attempted approximately halfway through incubation. The success rate for collection of blood or blood-tinged fluid from eggs was high, averaging 68% in the chicken eggs, 100% in the homing pigeon eggs, and 75% in the burrowing owl eggs. Collection did not affect subsequent hatchability. This blood could then be used to determine the sex of the embryo by utilizing a DNA probe or restriction fragment length polymorphism technique. Sex identification in ovo allowed the demographic management of small populations of birds within our institution.

Do land-use patterns influence nest-site selection by burrowing owls (Athene cunicularia hypugaea) in northeastern Colorado?

Populations of western burrowing owls (Athene cunicularia hypugaea) are declining. In the Great Plains this decline maybe related to a decline in black-tailed prairie dog (Cynomys ludovicianus) towns that the owls use for nest sites. One potential cause of prairie dog decline is conversion of native prairie to agriculture. We predicted that owl-occupied prairie dog towns would be in less fragmented landscapes that contain more prairie then owl-unoccupied prairie dog towns. To test this prediction, we used a geographic information system and spatial analysis metrics to examine the landscape within 1000 and 2500 m radius circles surrounding prairie dog towns in the shortgrass prairie in northeastern Colorado. We compared landscape features of irrigated cropland, non-irrigated cropland, and shortgrass patches around owl-unoccupied (N = 7) and owl-occupied (N = 15) prairie dog towns at these two spatial scales. Contrary to our predictions, at the 2500-m scale burrowing owls prefer to nest in towns surrounded by a landscape in which shortgrass patches were a smaller percentage of the total landscape, relatively far apart from other shortgrass patches, and more numerous then crop patches. At the 1000-m scale owls nested in towns in which shortgrass patches were a smaller percentage of the total surrounding landscape. In Logan County owls may select nest sites in prairie dog towns in more fragmented landscapes because prey availability maybe higher than in less fragmented landscapes and (or) prairie dog control programs may be more active on shortgrass rangelands than in croplands. In addition, the level of fragmentation in our study area (62% of the study area is occupied by native grassland) may not be high enough to have negative consequences on nest occupancy of burrowing owls. However, it is difficult to generalize about the effects of landscape fragmentation on burrowing owls because any effects are probably a complex function of local habitat structure, landscape structure, and local prey and predator availability.

Effects of Nest Dimensions on Use of Artificial Burrow Systems by Burrowing Owls

Although wildlife managers and researchers frequently use a variety of artificial burrow systems (ABS) to attract or supplement habitat for western burrowing owls (Athene cunicularia hypugaea), no previous studies have examined effects of ABS configuration on owl use. We examined choice of ABS configurations by nesting western burrowing owls in southwestern Idaho during 1997-98. To assess potential selection for chamber size, we placed clusters of 3 ABS around natural nest sites used 1995-97. Each cluster contained 3 burrows, each with a standard tunnel diameter but 3 different chamber sizes (707 cm 2 [small], 900 cm 2 [medium], and 1,750 cm 2 [large] of floor space). To assess potential choice for tunnel diameter, we placed clusters of 2 ABS in suitable burrowing owl habitat. These clusters offered 2 tunnel diameters (10 and 15 cm), each with a small chamber. Annual and combined distribution of use indicated that burrowing owls used ABS with large nest chambers and 10-cm-diameter tunnels. We detected no differences in clutch size or number of fledglings among chamber sizes, between tunnel diameters, or between cluster types (i.e., 2 or 3 ABS), although differences in number of fledglings between years exist ed for both types of clusters. Burrowing owls may use ABS with Iarge chambers and small tunnel diameters to reduce negative effects of overcrowding, to gain the most favorable microclimate for developing juveniles, or to help deter larger ground-dwelling predators. Our results indicate that researchers and resource managers interested in managing burrowing owl habitat should consider ABS composed of (1) chambers with >900 cm 2 of floor space, and (2) 10-cm-diameter tunnels.