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"Snow owl Behavior."
صنف حسب:
The snowy owl scientist
\"It's July on Alaska's North Slope, and scientist Denver Holt is in Utqiagvik surveying nests. Denver has been coming here since 1992, and the snowy owls he studies have been coming here much longer: thousands of years. With its mix of coastal, low-elevation tundra and a rich presence of lemmings, the North Slope is the only area in Alaska where snowy owls regularly nest. How do snowy owls decide where they will nest? How do they manage to arrive at locations where food will be abundant? What drives the success of these delicate tundra ecosystems? These are the mysteries Denver is trying to solve to help ensure a bright future for these elegant hunters.\" -- Amazon.com.
Book
Predation pressure by avian predators suggests summer limitation of small-mammal populations in the Canadian Arctic
Predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. We examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the Canadian Arctic. A dense and diverse suite of predatory birds, including the Snowy Owl (
Bubo scandiacus
), the Rough-legged Hawk (
Buteo lagopus
), and the Long-tailed Jaeger (
Stercorarius longicaudus
), inhabits the arctic tundra and prey on collared (
Dicrostonyx groenlandicus
) and brown (
Lemmus trimucronatus
) lemmings during the snow-free period. We evaluated the predation pressure exerted by these predators by combining their numerical (variation in breeding and fledgling numbers) and functional (variation in diet and daily consumption rates) responses to variations in lemming densities over the 2004-2010 period. Breeding density and number of fledglings produced by the three main avian predators increased sharply without delay in response to increasing lemming densities. The proportion of collared lemmings in the diet of those predators was high at low lemming density (both species) but decreased as lemming density increased. However, we found little evidence that their daily consumption rates vary in relation to changes in lemming density. Total consumption rate by avian predators initially increased more rapidly for collared lemming but eventually leveled off at a much higher value for brown lemmings, the most abundant species at our site. The combined daily predation rate of avian predators exceeded the maximum daily potential growth rates of both lemming species except at the highest recorded densities for brown lemmings. We thus show, for the first time, that predation pressure exerted without delay by avian predators can limit populations of coexisting lemming species during the snow-free period, and thus, that predation could play a role in the cyclic dynamic of these species in the tundra.
Journal Article
Rodent populations on the northern Great Plains respond to weather variation at a landscape scale
Extreme weather variation on the northern Great Plains of North America can potentially influence the abundance of grassland rodents across vast areas. We used the remains of 33,697 small mammals collected from owl pellets in central and western Canada over 15 years to determine the influence of weather on the annual abundance of deer mice (Peromyscus maniculatus), sagebrush voles (Lemmiscus curtatus), and meadow voles (Microtus pennsylvanicus). Weather variation affected the annual abundances of all 3 species; however, influence on deer mouse and sagebrush vole annual abundances was relatively small compared to that on meadow voles. This finding may indicate that factors other than weather (i.e., habitat availability) are more important for the abundance of deer mice and sagebrush voles at the landscape scale. In contrast, meadow voles were positively associated with the duration of snow cover above the hiemal threshold (20 cm), exhibiting up to 5-fold increases (i.e., irruptions) in abundance following winters of persistent, deep snow cover. Our study is the first to examine the effects of weather on landscape-scale abundance of rodent species on the northern Great Plains of North America, providing further insight into the role weather plays in driving rodent population fluctuations in this highly seasonal environment.
Journal Article
impact of climate and cyclic food abundance on the timing of breeding and brood size in four boreal owl species
The ongoing climate change has improved our understanding of how climate affects the reproduction of animals. However, the interaction between food availability and climate on breeding has rarely been examined. While it has been shown that breeding of boreal birds of prey is first and foremost determined by prey abundance, little information exists on how climatic conditions influence this relationship. We studied the joint effects of main prey abundance and ambient weather on timing of breeding and reproductive success of two smaller (pygmy owl Glaucidium passerinum and Tengmalm's owl Aegolius funereus) and two larger (tawny owl Strix aluco and Ural owl Strix uralensis) avian predator species using long-term nation-wide datasets during 1973-2004. We found no temporal trend either in vole abundance or in hatching date and brood size of any studied owl species. In the larger species, increasing late winter or early spring temperature advanced breeding at least as much as did high autumn abundance of prey (voles). Furthermore, increasing snow depth delayed breeding of the largest species (Ural owl), presumably by reducing the availability of voles. Brood size was strongly determined by spring vole abundance in all four owl species. These results show that climate directly affects the breeding performance of vole-eating boreal avian predators much more than previously thought. According to earlier studies, small-sized species should advance their breeding more than larger species in response to increasing temperature. However, we found an opposite pattern, with larger species being more sensitive to temperature. We argue that this pattern is caused by a difference in the breeding tactics of larger mostly capital breeding and smaller mostly income breeding owl species.
Journal Article
Demography Of Northern Flying Squirrels Informs Ecosystem Management Of Western Interior Forests
We studied northern flying squirrel (Glaucomys sabrinus) demography in the eastern Washington Cascade Range to test hypotheses about regional and local abundance patterns and to inform managers of the possible effects of fire and fuels management on flying squirrels. We quantified habitat characteristics and squirrel density, population trends, and demography in three typical forest cover types over a four-year period. We had 2034 captures of flying squirrels over 41 000 trap nights from 1997 through 2000 and marked 879 squirrels for mark-recapture population analysis. Ponderosa pine (Pinus ponderosa) forest appeared to be poorer habitat for flying squirrels than young or mature mixed-conifer forest. About 35% fewer individuals were captured in open pine forest than in dry mixed-conifer Douglas-fir (Pseudotsuga menziesii) and grand fir {Abies grandis) forests. Home ranges were 85% larger in pine forest (4.6 ha) than in mixed- conifer forests (2.5 ha). Similarly, population density (Huggins estimator) in ponderosa pine forest was half (1.1 squirrels/ha) that of mixed-conifer forest (2.2 squirrels/ha). Tree canopy cover was the single best correlate of squirrel density (r = 0.77), with an apparent threshold of 55% canopy cover separating stands with low-from high-density populations. Pradel estimates of annual recruitment were lower in open pine (0.28) than in young (0.35) and mature (0.37) forest. High recruitment was most strongly associated with high understory plant species richness and truffle biomass. Annual survival rates ranged from 45% to 59% and did not vary among cover types. Survival was most strongly associated with understory species richness and forage lichen biomass. Maximum snow depth had a strong negative effect on survival. Rate of per capita increase showed a density-dependent response. Thinning and prescribed burning in ponderosa pine and dry mixed conifer forests to restore stable fire regimes and forest structure might reduce flying squirrel densities at stand levels by reducing forest canopy, woody debris, and the diversity or biomass of understory plants, truffles, and lichens. Those impacts might be ameliorated by patchy harvesting and the retention of large trees, woody debris, and mistletoe brooms. Negative stand-level impacts would be traded for increased resistance and resilience of dry-forest landscapes to now-common, large-scale stand replacement fires.
Journal Article
Dietary Trends of Barn Owls in an Agricultural Ecosystem in Northern Utah
Barn Owl (Tyto alba) diets were studied for 15 years in Utah. Ninety-eight percent of 111,016 prey items were mammals, heavily dominated by voles (Microtus spp.). Food-niche breadth (FNB) was 3.33 for the entire sample and varied gradually but significantly among the 15 years and among seasons. Frequency of prey in the diet did not vary significantly from year to year or among seasons. Mean daily temperatures did not vary significantly among years but annual precipitation totals and days when deep snow covered the ground varied significantly among years. Irrigation for agriculture may have partially mitigated annual precipitation fluctuations. Hay, one of the most important crops on the study area, increased over the study period and other crops decreased slightly in the amount planted. Hectares of hay planted, hectares of corn planted, and hectares of barley planted were the variables that combined to best predict annual FNB.
Journal Article
The night witches
Anna: An owl kills in utter silence. I saw one beside the airfield, the great wings outspread, slowly falling and rising with a small shape dangling from its mouth. We are like those owls, stealth hunters of the night. Our prey have another name for us.
Pah! We are the Glorious Bomber Guards, and we kill Fascists!
Alex: I met Sasha via the internet, and we met for drinks, after work one night. She was taller and more slender than she looked in the photo, a cap of dark, shiny hair, wearing work clothes of different hues, but all one tone short of being black. Just like me, in fact. And so began the longest date of my life.
Journal Article
Post-Fledging Ecology of Northern Pygmy-Owls in the Rocky Mountains
We investigated the post-fledging ecology of the Northern Pygmy-Owl (Glaucidium gnoma) at two study areas in the Rocky Mountains of Montana and Idaho from 2002 to 2009. We observed 16 successful nesting attempts that fledged from two to seven young. Fledging dates ranged from 18 June to 5 August and all nests were vacated within a 2-day period. Post-fledging behavioral data were collected regularly from fledging through initiation of natal dispersal from five radiomarked family groups and opportunistically from three additional family groups. Post-fledging movement data were collected from eight family groups and two males that were suspected of nesting. Adults attended broods for 9 to 30 days (females) and 31 to 34 days (males) postfledging, after which they were not observed associating with their young. Young remained within the natal territory for 1 to 10 days following departure of adult males, after which they abruptly initiated natal dispersal. Areas used by family groups during the post-fledging dependency period ranged from 34.6 to 94.5 ha. Family groups were active throughout the day, but activity was notably more intense during crepuscular periods. Our earliest observations of young hunting occurred 9 days after fledging and 47% of all fledgling hunting attempts observed (n = 75) were successful. Adults and fledglings used vocalizations in contexts consistent with previous descriptions with the exception of an undescribed two-note vocalization that appeared to function as a contact call preceding prey deliveries.
Journal Article
ENVIRONMENTAL CONDITIONS AFFECT OFFSPRING SEX-RATIO VARIATION AND ADULT SURVIVAL IN TAWNY OWLS
We studied survival of adult Tawny Owls (Strix aluco), number of breeding pairs, breeding performance, and offspring sex ratio in relation to the number of snowy days in the preceding winter in Duna-Ipoly National Park, Hungary. A new male was more likely to be present after a winter with many snowy days, although female survival was not affected by weather. Number of breeding pairs and number of fledglings declined with increasing number of snowy days. Offspring sex ratio varied according to whether snow cover was present during the egg-laying period, with broods being male biased during adverse conditions but female biased during mild conditions. Also, female nestlings were more likely to die before fledging than male nestlings. These data suggest that female Tawny Owls are able to adjust the sex ratio of their brood according to the expected differential success of nestlings under the prevailing weather conditions. This adjustment in relation to environmental conditions has important implications for the demography of Tawny Owl breeding populations. Las Condiciones Ambientales Afectan la Variación en el Cociente de Sexos de las Crías y la Supervivencia de los Adultos en Strix aluco Resumen. Estudiamos la supervivencia de los adultos de Strix aluco, el número de parejas reproductivas, el desempeño reproductivo y el cociente de sexos de las crías con relación al número de días con nieve en el invierno precedente en el Parque Nacional Duna-Ipoly, Hungría. Un macho nuevo tuvo mayor probabilidad de estar presente luego de un invierno con muchos días con nieve, aunque la supervivencia de las hembras no estuvo afectada por el clima. El número de parejas reproductivas y el número de volantones disminuyeron con un incremento en el número de días con nieve. El cociente de sexos de las crías varió de acuerdo con la presencia de cobertura de nieve durante el período de puesta de los huevos: las nidadas estuvieron sesgadas hacia los machos durante períodos de condiciones adversas y sesgadas hacia las hembras durante períodos de condiciones moderadas. Además, los pichones hembra tuvieron mayor probabilidad de morir antes de dejar el nido que los machos. Estos datos sugieren que las hembras de S. aluco son capaces de ajustar el cociente de sexos de sus nidadas de acuerdo al éxito diferencial esperado de los pichones bajo las condiciones climáticas dominantes. Este ajuste relacionado con las condiciones ambientales tiene implicancias importantes para la demografía de las poblaciones reproductivas de S. aluco.
Journal Article
Forest PHANTOM
[...]they are known to be able to locate a mouse or vole underneath significant snow cover. When they sense a mouse or vole is available, they will silently lift off, approach the rodent, and then fold their wings and dive bomb into the snow, spreading their talons to maximum extension and bringing their feet forward at the last instant. Species Spotlight: GREAT GRAY OWL * LENGTH: 2-2'A feet * WINGSPAN: 4'Á feet * WEIGHT: 2-3 lbs. * RANGE:
Journal Article