Owl Nests Research Articles

Effects of survey methods on burrowing owl behaviors

AbstractMonitoring wildlife populations often involves intensive survey efforts to attain reliable estimates of population size. Such efforts can increase disturbance to animals, alter detection, and bias population estimates. Burrowing owls (Athene cunicularia) are declining across western North America, and information on the relative effects of potential survey methods on owl behaviors is needed. We designed a field experiment to compare burrowing owl flight distances, times displaced, and probabilities of being displaced between 4 potential population survey methods (single walking surveyor, single vehicle stop, single vehicle stop with 2 surveyors, and double vehicle stop with 2 surveyors), and an experimental control in the agricultural matrix of Imperial Valley, California. Between 25 April and 1 May 2008, we randomly applied survey methods to 395 adult male owls during daylight hours (0700 hours through 1900 hours). All survey methods increased odds of displacing owls from perches. Survey methods with observers outside the vehicle were 3 times more likely to displace an owl than a single vehicle stop where observers remained inside the vehicle. Owls were displaced farther distances by all survey methods compared to control trials, but distances and time displaced did not differ among survey methods. We recommend that surveys for counting owls during the breeding season in agroecystems like the Imperial Valley where high densities of owls nest primarily along the borders of fields be conducted using single vehicle stops with or without 2 surveyors, depending on conditions for locating owls from roads. © 2011 The Wildlife Society.

Efficient Placement of Nest Boxes for the Little Owl (Athene noctua)

The use of artificial nest boxes to bolster populations of endangered cavity-nesting birds has increased significantly, but spatial variation of nest-box occupancy rates and breeding success within a nest-box population has been little studied. In a case study with 798 Little Owl (Athene noctua) nest boxes established in central Germany, we analyzed the dependence of occupancy rate and breeding success on the characteristics of the surrounding habitat. The analysis focused on two aspects of general concern for nest-box management: (1) whether nest boxes were occupied for breeding or were left unoccupied, and (2) whether Little Owls had different reproductive rates, depending on the location of nest boxes. A high resolution (1 × 1 m) land-use map was used to analyze species-habitat relationships, and Generalized Linear Mixed Models were used to predict suitable nest-box locations. During the period from 2004 to 2006, 544 (68%) of the nest boxes were never occupied, 144 (18%) housed birds with low breeding success and only 108 (14%) housed pairs that produced more than 2.35 nestlings annually, a reproductive rate thought necessary for population stability. Nest boxes were more likely to be occupied if they were located near orchards, at lower altitude, and in areas of higher densities of fields and less forest. Higher breeding success was associated with fallow fields and field margins, and with greater distance to roads and forests. Our results suggested that the efficiency of this nest-box program could be substantially increased if unoccupied nest boxes were relocated to sites where occupancy is more likely, and if unproductive nest boxes were relocated to locations that would enhance breeding success.

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.

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.

Microhabitat Features at Mexican Spotted Owl Nest and Roost Sites in the Guadalupe Mountains

Abstract In some portions of their range, Mexican Spotted Owls (Strix occidentalis lucida) are found occupying conifer-dominated forests, whereas in other portions of their range, they occupy narrow and steep-walled canyons. Although the characteristics of this owl's nesting and roosting habitat have been studied extensively in predominately forested environments, there is far less information describing microhabitat features associated with nesting and roosting sites in canyon systems. In this report, we quantitatively describe microhabitat characteristics of nest and roost sites of Mexican Spotted Owls within the Guadalupe Mountains of southeastern New Mexico and west Texas, where Spotted Owls dwell primarily in narrow, rocky, and semiarid canyons. We measured 21 habitat features describing the geomorphology of the canyon and finer-scaled variables at accessible owl nest or roost sites (n = 10) and at nearby random sites up- (n = 10) and down-canyon (n = 10); we found that tree canopy cover (%) wa...

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...

Temporal Instability of Agricultural Habitat Reduces Reproductive Success of Barn Owls (Tyto alba)

ABSTRACT. Birds are generally unable to predict future changes in habitat condition when selecting nesting locations, and few studies have investigated the effect on birds of shifting habitat quality within nesting seasons. Anthropogenically influenced habitats such as agricultural landscapes are often associated with large shifts in quality that turn initially good habitat into poor habitat. We examined whether daily survival rates of Barn Owl (Tyto alba) nests in an agricultural landscape were influenced negatively by temporal instability in habitat conditions resulting from crop harvest. Although most nesting attempts by Barn Owls in our study area were initiated before the onset of harvest, fields adjacent to the majority of active nest boxes were harvested at some point during nesting attempts. Overall nest survivorship, as well as survivorship of individual nestlings within broods, was lower following harvest, likely because of associated declines in the abundance of rodents, the primary food source...

Using Topography to Meet Wildlife and Fuels Treatment Objectives in Fire-Suppressed Landscapes

Past forest management practices, fire suppression, and climate change are increasing the need to actively manage California Sierra Nevada forests for multiple environmental amenities. Here we present a relatively low-cost, repeatable method for spatially parsing the landscape to help the U.S. Forest Service manage for different forest and fuel conditions to meet multiple goals relating to sensitive species, fuels reduction, forest products, water, carbon storage, and ecosystem restoration. Using the Kings River area of the Sierra Nevada as a case study, we create areas of topographically-based units, Landscape Management Units (LMUs) using a three by three matrix (canyon, mid-slope, ridge-top and northerly, southerly, and neutral aspects). We describe their size, elevation, slope, aspect, and their difference in inherent wetness and solar radiation. We assess the predictive value and field applicability of LMUs by using existing data on stand conditions and two sensitive wildlife species. Stand conditions varied significantly between LMUs, with canyons consistently having the greatest stem and snag densities. Pacific fisher (Martes pennanti) activity points (from radio telemetry) and California spotted owl (Strix occidentalis occidentalis) nests, roosts, and sightings were both significantly different from uniform, with a disproportionate number of observations in canyons, and fewer than expected on ridge-tops. Given the distinct characteristics of the LMUs, these units provide a relatively simple but ecologically meaningful template for managers to spatially allocate forest treatments, thereby meeting multiple National Forest objectives. These LMUs provide a framework that can potentially be applied to other fire-dependent western forests with steep topographic relief.

Utility of Helicopters for Short-eared Owl Nest Searches and Surveys

Utility of Helicopters for Short-eared Owl Nest Searches and Surveys

Ural Owl Predation on Field Voles and Bank Voles by Size, Sex and Reproductive State

Predation on selected individuals from a population may have consequences for the prey population. We studied predation of breeding Ural owls (Strix uralensis) in southern Finland on their two main prey species, field voles (Microtus agrestis) and bank voles (Myodes glareolus), which fluctuate in abundance between years. We identified sex, body mass and reproductive state of the voles in Ural owl nests and of voles caught by snap-trapping in the study area. Our results showed that Ural owls preyed proportionally more upon reproductively active field voles than expected, whereas no such bias was found for predation on bank voles. There was no difference in sex ratio between preyed upon and trapped field voles or bank voles. Ural owls captured heavier individuals of both field voles and bank voles than expected, and in field voles, but not bank voles, reproductively active individuals were heavier than reproductively inactive individuals. We discuss how differences in social organisation, dispersal and reproductive behaviour may differently affect predation vulnerability of field voles and bank voles. In contrast to the pattern documented in other owl species, we find that Ural owls select larger and reproductively active voles, and may thereby exert a higher population-dynamical impact on vole populations than expected solely from the numbers of voles preyed upon.

From Carolyn Jackson

from Carolyn Jackson Carolyn Jackson A clerk in a Moab, Utah, bookstore suggested that I read something by Terry Tempest Williams after I exhausted its supply of Edward Abbey titles, and I’m glad she did. Born in 1955, Williams is a worthy successor to Abbey, who lived in the desert Southwest and died in 1989. A naturalist by education and vocation, Williams has the gift of seeing universality in the specific, whether she’s at the Great Salt Lake or in a Rwandan village. She is also a spiritual seeker—raised a fifth-generation Mormon, but a dissenter from some Latter Day Saints teachings. Where Abbey’s quest led to civil disobedience, Williams’s might lead to a hair-raising vision or a profound insight. Refuge: An Unnatural History of Family and Place Terry Tempest Williams Pantheon, 1991, Out of Print. 320 pages, Available in Vintage Paperback, $13.95. [End Page 171] This is Williams’s masterpiece. She wrote it in a time of impending change: a rise in water level was destroying the wildlife sanctuary in the Great Salt Lake, where she studied migratory birds; her mother, Diane, developed ovarian cancer; and a developer had big plans for the neighborhood in Salt Lake City where she and her artist husband, Brooke, lived contentedly. I think the book’s strength comes from Williams’s discipline in moving between her deep mourning for what is being lost and her ability to focus on the exquisite beauty that is immediately before her—whether it’s a rare snow bunting, or a deep navy bathrobe with tiny stars that her mother buys. Her analogies come effortlessly. “After supper, we would spread out our sleeping bags in a circle, heads pointing to the center like a covey of quail, and watch the Great Basin sky fill with stars,” she recalls of family camping trips. “Our attachment to the land was our attachment to each other.” Williams’s ancestors came to Utah pushing carts 150 years ago. She draws strength from this, but at the same time, there is a palpable tension between her independent spirit (she gives the finger to a bunch of yahoos who destroy a burrowing owl nest) and the patriarchal norms of the church. She is proudly feminist, having grown up with the example of strong women like her mother, who fought off breast cancer when her four children were young, and her grandmother Mimi, who took her on her first Audubon field trip when she was nine. Sadly, by the time the book ends, Williams is 34 years old and already the matriarch of her family. In a chapter called “The Clan of One-Breasted Women,” we learn the meaning of the title’s reference to an unnatural history. Leap Terry Tempest Williams Pantheon, 2000, Out of Print. 352 Pages, Available in Vintage Paperback, $16.95. When we catch up with Williams almost a decade later, she and Brooke have moved to the Red Rock country of southeastern Utah. But this book is set in Madrid, where she has communed intermittently for seven years with Hieronymus Bosch’s painting El jardin de las delicias in the Prado museum. This triptych from the fifteenth century is referred to in English as The Garden of Earthly Delights, but as a girl, Williams was familiar only with the outer panels—Adam and Eve with Jesus in Paradise, and Hell on the other side. They were tacked to the wall over the bed where she slept in her grandparents’ [End Page 172] home. Only as an adult did she discover the magnificent center panel. (A reproduction of the painting comes with the book.) Williams moves fluidly from the Prado to Utah, in and out of her own psyche, and inside the painting as a contained world. She obviously knows her way around an art studio, but her naturalist’s eye finds 35 species of birds in The Garden. There’s something else here: Williams is a religious mystic. In Refuge, she wrote, “I was raised to believe in a spirit world, that life exists before the earth and will continue to exist afterward, that each human being, bird and bulrush, along with all...

Habitat selection as an antipredator behaviour in a multi‐predator landscape: all enemies are not equal

1. Breeding territory choice constitutes a crucial antipredator behaviour for animals that determines reproductive success and survival during the breeding season. On arrival to breeding grounds migrant prey face a multitude of 'waiting' predators already settled within the landscape. 2. We studied territory selection and reproductive investment of migrant pied flycatcher (Ficedula hypoleuca) relative to breeding pygmy owls (POs) (Glaucidium passerinum) and Tengmalm's owls (TOs) (Aegolius funereus). Diurnal POs present a greater predation threat to adult flycatchers (up to 80% songbirds in diet) compared with nocturnal TOs (up to 36%). 3. During territory selection, pied flycatchers strongly avoided POs (occupation: 42% in presence vs. 92% in absence of owl nest) but not TOs (80% vs. 75%). This suggests that flycatchers are able to distinguish between two potential predators, avoiding dangerous POs but not obviously responding to the less risky TOs. 4. Flycatchers responded to presence of PO nests with c. 4-day delay in the start of egg-laying. A significantly prolonged nest building period contributed to this potentially costly breeding delay. Flycatchers further significantly reduced initial reproductive investment in presence of POs by laying 8.2% smaller clutch sizes, even if laying date was controlled. No breeding delay and clutch size reduction was found relative to TO presence. 5. Our results highlight flexibility in breeding territory selection and reproductive strategies as antipredator responses to perceived risk in a multi-predator environment. This supports the idea that for prey, not all predators are equal.

Experimental increase in food supply influences the outcome of within-family conflicts in Tengmalm’s owl

Within a family there are conflicts of interest between parents and offspring, and between male and female parents, over the supply of parental care. The observed pattern of parental care is the outcome of negotiations within the family, and may be influenced by environmental factors such as food abundance. We experimentally increased food supply to ten Tengmalm’s owl (Aegolius funereus) nests from hatching to fledging, mimicking natural cached prey. Ten un-supplemented nests served as controls. Parents and offspring were fitted with radio-tags. Food provisioning by parents was measured both in the (1) mid- and (2) late nestling stage and in the (3) early and (4) late post-fledging stage. In response to food supplementation, both males and females reduced food provisioning, but the effect was more pronounced in females. Females generally contributed much less to food provisioning than males, and food supplementation increased the difference between the sexes. Mass loss during the brooding stage was substantially lower for supplemented than for control females. Food supplementation did not improve offspring survival, and had no effect on body measurements of nestlings. In conclusion, parents of both sexes used the increased food supply to reduce the costs of caring for their current offspring, but females responded more strongly than males.

Formation of aggregated settlements as an expression of synanthropization of the long-eared owl (Asio otus L.)

The structure of the long-eared owl (Asio otus L.) settlements in anthropogenic landscapes has been studied in the Zhuravlinaya Rodina protected territory in the northern Moscow region in 2001–2005. The possible factors that cause the formation of such settlements have been analyzed. The differences in the breeding success between owls nesting near and away from human settlements have been estimated. Aggregated nesting of owls is assumed to be mainly related to a lower predator pressure in the vicinity of human dwellings in the incubation period. Aggregated nesting is regarded as an expression of synanthropization of the species.

Long-Term Study on Interactions between Tawny OwlsStrix aluco, JackdawsCorvus monedulaand Northern GoshawksAccipiter gentilis

We monitored the dynamics of owls, raptors and corvids within the 3400 ha of the Amsterdam Water Supply Dunes in the western Netherlands from 1961 through 2007. In the 1930s and 1950s, afforestation projects were initiated. In 1961 the first Tawny Owl nest was found, from whence the population increased steadily to stabilize in the 1970s at c. 24 pairs. Tawny Owl dynamics were affected by competition for nest sites with Jackdaws Corvus monedula and depredation by Northern Goshawks Accipiter gentilis. Jackdaws were able to take over nest boxes from egg laying and incubating Tawny Owls, reducing the letter's breeding success. Tawny Owl numbers and breeding success were negatively correlated with Jackdaw numbers (R2 = 0.556 and R2 = 0.592, respectively). After the first nest in 1993, Goshawk numbers rapidly increased to 10–11 pairs in 1999. The number of Jackdaw breeding pairs correlated negatively with the number of Goshawks (R2 = 0.661). Goshawks apparently limited Jackdaw numbers, which led to an improvement of Tawny Owl breeding success. However, post-fledging mortality of Tawny Owl from Goshawk predation was also significant, reducing local recruitment in the Tawny Owl breeding population.

Breeding and Population Density of the Eastern Screech OwlMegascops asioat the Northern Periphery of Its Range

Random-stratified spring nocturnal surveys using tape playback were conducted for Eastern Screech Owls Megascops asio from 2004 through 2007 in Winnipeg, Manitoba, Canada, at the northern periphery of its range. Surveys were stratified by (1) human density, (2) riparian vs. non-riparian habitat, and 3) the presence or absence of suburban greenspace. A total of 120 transects (each 1.75 km long) were surveyed, with 55 Eastern Screech Owls detected. Eastern Screech Owl densities peaked in moderate to high-density suburban areas (>20 persons/ha), where 36 (66%) detections occurred, and were lowest in wildlands (<1 pair/ha), where no detections occurred. Fifty-one (93%) Eastern Screech Owls were detected in riparian areas. Only 20 (36%) Eastern Screech Owls were detected in suburban greenspaces. In 4 years I located a total of 46 successful Eastern Screech Owl nests, 6 failed nests, and 37 territories with non-breeding owls. Excluding repeat cavity uses, a total of 61 nest sites and territory centres were located, of which 38 (62.3%) were in natural cavities, 21 (34.4%) in nest boxes, and 2 (3.3%) at sites where cavity choice was undetermined. Fledging dates ranged from 28 May – 3 July (mean 15 June, SE 1.4) over the 4-year period. Eastern Screech Owls were closely tied to riparian habitat, and showed larger average brood sizes and earlier average fledging dates in moderate and high-density suburban areas than in low-density suburban and rural areas.

Red-breasted goose colonies on the Taimyr Peninsula: Factors responsible for the proximity of goose nests to nests of peregrine falcons, rough-legged buzzards, and snowy owls

Red-breasted goose colonies have been studied near Medusa Bay (73 degrees 21' N, 80 degrees 32' E), on the northwestern Taimyr Peninsula, and along the Agapa River (70 degrees 11' N, 86 degrees 15' E) down to its mouth (70 degrees 26' N, 89 degrees 13' E), in the central Taimyr Peninsula. Red-breasted geese nesting near peregrine falcons are protected by the falcons from arctic foxes; however, they are sometimes attacked by the falcons themselves. In the colonies near peregrine falcon nests, the vast majority of goose nests were situated no farther than 100 m from the falcon nest. When food is abundant, falcons protect a larger area around their nest. The distance between the falcon nest and the surrounding goose nests is inversely related to the falcon's activity. In years of higher falcon activity, falcons prevent red-breasted geese from nesting as close to their nest as in years of lower falcon activity. Additional stimuli are required for red-breasted geese to form colonies near rough-legged buzzard nests. The distance between snowy owl nests and red-breasted goose nests was smaller when arctic foxes were abundant than when they were scarce.

A sample of prey remains found in great-horned owl nests in Saskatchewan in 2008

A sample of prey remains found in great-horned owl nests in Saskatchewan in 2008

Effect of cyclic and declining food supply on great grey owls in boreal Sweden

In this study of 35 years of data, we examine the short-term (cyclic) and long-term relationship between breeding success of great grey owls ( Strix nebulosa Forster, 1772) and their food supply (bank voles ( Clethrionomys glareolus (Schreber, 1780)), grey-sided voles ( Clethrionomys rufocanus (Sundevall, 1846)), and field voles ( Microtus agrestis (L., 1761))) in northern Sweden. Annual number of owl nests showed a 3 year cyclicity, which as predicted, corresponded to the length of the vole cycle in the region. Mean annual brood size also fluctuated and was positively dependent on the vole supply during the same spring. In this region, there has also been a decline in vole numbers in recent decades, from high-amplitude cycles in the 1970s to subsequent low-amplitude cycles. Correspondingly, and as predicted, mean annual brood size of the owls also declined, although only during the third years of the vole cycle when vole supply in spring and brood size of the owls is at its highest level in high-amplitude cycles. We predict that in the long run the vole decline, associated with increasingly milder winters, and the reduction of the brood size of the owls, especially in years of high owl breeding success, will have serious implications for the population of great grey owls in Scandinavia.

Does Doramectin Use on Cattle Indirectly Affect the Endangered Burrowing Owl

Doramectin is one of several endectocide compounds widely used to treat nematode and arthropod pests affecting cattle. Insecticidal residues in dung of endectocide-treated cattle can reduce numbers of dung-breeding insects. Concerns have been raised that use of endectocides may adversely affect birds that rely on dung-breeding insects as food. However, these concerns have not been specifically addressed in previous studies. We performed two studies to collectively assess whether doramectin adversely affects burrowing owls (Athene cunicularia Molina), which are listed as ‘‘Endangered’’ in Canada. In the first study, insect emergence was monitored from dung of cattle treated with a recommended topical dose of doramectin. Experiments replicated in each of 3 yr showed residues reduce the number of insects developing in dung of cattle treated up to 16 wk previously. In the second study, we identified prey items from regurgitated pellets collected at 206 burrowing owl nests in southern Alberta and Saskatchewan, Canada. A total of 50 213 prey items were identified, of which 90% were invertebrates. Beetles (Coleoptera) comprised 54% of the total prey items, followed next in abundance by grasshoppers (Acrididae, 20%) and crickets (Gryllidae, 16%). Of the beetles, 1 381 specimens were identified as breeding in dung (mainly species of Aphodius, Canthon, Onthophagus). The dung beetles comprised an estimated 2.8% of the total prey items or 0.1% of total prey biomass. Results of the first study validate initial concerns that doramectin use can reduce numbers of insects breeding in dung of treated cattle. Results of the second study show reliance of burrowing owls on dung beetles is sufficiently low that use of doramectin on cattle is unlikely to appreciably affect the food supply of co-occurring burrowing owls.