Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
302
result(s) for
"Snow owl."
Sort by:
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
Birdscapes
What draws us to the beauty of a peacock, the flight of an eagle, or the song of a nightingale? Why are birds so significant in our lives and our sense of the world? And what do our ways of thinking about and experiencing birds tell us about ourselves? Birdscapes is a unique meditation on the variety of human responses to birds, from antiquity to today, and from casual observers to the globe-trotting \"twitchers\" who sometimes risk life, limb, and marriages simply to add new species to their \"life lists.\"
Drawing extensively on literature, history, philosophy, and science, Jeremy Mynott puts his own experiences as a birdwatcher in a rich cultural context. His sources range from the familiar--Thoreau, Keats, Darwin, and Audubon--to the unexpected--Benjamin Franklin, Giacomo Puccini, Oscar Wilde, and Monty Python. Just as unusual are the extensive illustrations, which explore our perceptions and representations of birds through images such as national emblems, women's hats, professional sports logos, and a Christmas biscuit tin, as well as classics of bird art. Each chapter takes up a new theme--from rarity, beauty, and sound to conservation, naming, and symbolism--and is set in a new place, as Mynott travels from his \"home patch\" in Suffolk, England, to his \"away patch\" in New York City's Central Park, as well as to Russia, Australia, and Greece.
Conversational, playful, and witty, Birdscapes gently leads us to reflect on large questions about our relation to birds and the natural world. It encourages birders to see their pursuits in a broader human context--and it shows nonbirders what they may be missing.
eBook
Juvenile survival of little owls decreases with snow cover
Global environmental changes are associated with warmer average temperatures and more extreme weather events, potentially affecting wildlife population dynamics by altering demographic processes. Extreme weather events can reduce food resources and survival in all seasons of the year. Estimates of season‐specific survival probabilities are therefore crucial to understand the moderating effect of extreme events on annual mortality. Here, we analysed survival probabilities of 307 radio‐tracked juvenile little owls (Athene noctua) over two‐week periods from fledging to their first breeding attempt in the following spring to assess the contribution of extreme weather events. Survival probabilities were typically lowest during the first weeks after fledging in summer but were moderated by seasonal extremes in winter. The duration of snow cover in winter had a strong negative effect on survival probability, while being food supplemented during the nestling stage increased survival during the first weeks after fledging in summer and ultimately led to a larger proportion of birds surviving the first year. Overall annual survival probability over the first year varied by 34.3% between 0.117 (95% credible interval 0.052–0.223) and 0.178 (0.097–0.293) depending on the severity of the winter, and was as high as 0.233 (0.127–0.373) for food‐supplemented fledglings. In years with mild winters, the season with the lowest survival was the summer post‐fledging period (0.508; 0.428–0.594), but in years with extensive snow cover the winter was the season with the lowest survival (0.481; 0.337–0.626). We therefore show that extreme weather events occurring in a particular season reduced the proportion of first‐year survivors. Increasing extreme weather events can moderate seasonal survival probability through altering food supply of juvenile little owls either during the nestling period or in winter, with similarly large effects on annual survival and the viability of populations. Climatic changes can affect the survival of young birds and populations. Using high‐resolution telemetry, we show that annual juvenile survival of little owls can be reduced by 34% during harsh winters. Warmer winters with less snow may therefore improve juvenile survival.
Journal Article
Camouflage efficiency in a colour‐polymorphic predator is dependent on environmental variation and snow presence in the wild
Colour polymorphism can be maintained by colour morph‐specific benefits across environmental conditions. Currently, the amount and the duration of snow cover during winter decrease especially in northern latitudes, which can alter the potential for camouflage of animals with light and dark morphs. Tawny owls, Strix aluco, are colour‐polymorphic avian predators with dark (brown) and light (grey) colour morphs, where the grey morph is presumed to enjoy camouflage benefits under snowy conditions. We studied the camouflage potential of morphs in two tawny owls potential using passerines' probability to mob in the wild during winter with and without snow. For comparison with other seasons, we also repeated the experiment during spring and autumn. We found that grey tawny owls have a lower probability of being mobbed than the brown tawny owls only during snowy winters. The two colour morphs therefore experience differential benefits across snow conditions, which may help to maintain colour morphs in the population, although further warming of winter climate will reduce the potential for camouflage for grey tawny owls in northern latitudes. You better be a grey tawny owl, if you live in snowy conditions and want to minimize harassment. Using an experimental approach with stuffed tawny owls of the grey and brown morph, we show that grey tawny owls are less mobbed than brown tawny owls during snowy winters. In the other seasons, both morphs are equally detected.
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
Interactive influences of fluctuations of main food resources and climate change on long-term population decline of Tengmalm’s owls in the boreal forest
Recent wildlife population declines are usually attributed to multiple sources such as global climate change and habitat loss and degradation inducing decreased food supply. However, interactive effects of fluctuations in abundance of main foods and weather conditions on population densities and reproductive success have been studied rarely. We analysed long-term (1973–2018) data on Tengmalm’s owl (
Aegolius funereus
) and the influence of prey abundance and weather on breeding densities and reproductive success in western Finland. We found that fledgling production per breeding attempt declined and laying date of the owl population delayed during the period between 1973 and 2018. The breeding density of the owl population decreased with increasing temperature in winter (October–March), fledgling production increased with increasing temperature and precipitation in spring (April–June), whereas the initiation of egg-laying was delayed with increasing depth of snow cover in late winter (January–March). The decreasing trend of fledgling production, which was mainly due to starvation of offspring, was an important factor contributing to the long-term decline of the Tengmalm’s owl study population. Milder and more humid spring and early summer temperatures due to global warming were not able to compensate for lowered offspring production of owls. The main reason for low productivity is probably loss and degradation of mature and old-growth forests due to clear-felling which results in loss of coverage of prime habitat for main (bank voles) and alternative foods (small birds) of owls inducing lack of food, and refuges against predators of Tengmalm’s owls. This interpretation was also supported by the delayed start of egg-laying during the study period although ambient temperatures increased prior to and during the egg-laying period.
Journal Article
Western spotted skunk spatial ecology in the temperate rainforests of the Pacific Northwest
A major threat to small mammalian carnivore populations is human‐induced land use change, but conservation and management are inhibited by limited knowledge about their ecology and natural history. To fill a key knowledge gap of the western spotted skunk (Spilogale gracilis), we investigated their spatial ecology at the landscape and home range scale in the temperate rainforests of the Oregon Cascades during 2017–2019. For the landscape scale analysis, we used detections of western spotted skunks at 112 baited camera traps and fitted a dynamic occupancy model to investigate spatial distribution and drivers of inter‐seasonal and inter‐annual changes in occupancy. Concurrently, we radio‐collared 25 spotted skunks (9 female, 16 male) and collected 1583 relocations. Using continuous‐time movement models, we estimated large home range sizes for both male and female spotted skunks, relative to their body mass, and highly overlapping home ranges that indicated a lack of territoriality. Using these home ranges, we fitted a resource selection function using environmental covariates that we assigned to various hypotheses such as resources, predator avoidance, thermal tolerance, and disturbance. Overall, western spotted skunks were widely distributed across our study area (seasonal occupancy up to 63.7 ± 5.3%) and highly detectable (weekly detection probability = 41.2%). At both spatial scales, spotted skunks selected wetter areas and local valleys, which we attributed to areas with more food resources. At the home range scale, spotted skunks selected locations with lower predation risk and areas surrounded by more previously logged forests. In this montane environment, inter‐seasonal contractions in the spatial distributions of spotted skunks were strongly driven by their response to cold temperature and accumulated snow. This was especially evident when seasonal occupancy declined significantly following a severe heavy snow event in February 2019. Given that there is little information available on the natural history of the western spotted skunk, these results provide essential information about their ecology to focus future monitoring efforts and may help identify potential threats (e.g., forest management, severe snow events, or wildfires) to this species.
Journal Article
Residual forest structure influences behaviour of Pacific marten (Martes caurina) on post-fire landscapes
Wildfires are broad-scale disturbances in North American forests, with impacts that persist for many decades. Further disturbance from post-fire salvage logging is extensively modifying burned landscapes. The removal of habitat structure by fire and salvage logging may affect the persistence of forest-specialist wildlife such as Pacific marten (Martes caurina). However, it is unclear which resources are important to marten on burned landscapes. We used snow tracking and habitat surveys to examine marten habitat selection after three large fires in north-central Washington, USA (10–13 years post-fire), and central British Columbia, Canada (1–2 and 6–9 years post-fire). We developed site-scale habitat models to explain marten foraging and scent-marking post-fire, and assessed further structural changes from salvage logging. Foraging marten chose sites with lower burn severity, greater canopy closure, more vertical structures (trees, snags, saplings, and shrubs), and greater moss/lichen cover than what was generally available. When scent-marking, marten selected structurally-complex sites with abundant deadfall or saplings. Marten moved more quickly when canopy cover was sparse, and rarely used salvage-logged areas. Our results suggest that marten rely on residual habitat structure within large burns, and that secondary disturbance from salvage logging is substantially more harmful to marten than the original fire.
Journal Article
Diverse historical fire disturbance and successional dynamics in Douglas‐fir forests of the western Oregon Cascades, USA
We created the first annually resolved records of historical fire occurrence coupled with precise estimates of tree establishment for the northern half of the west slope of the Oregon Cascades, a region that is home to some of the most productive forests on earth. Our reconstructions at 36 randomly located sites document exceptional diversity in historical fire disturbance and successional dynamics. Most stands where we collected data appear to have initiated following stand‐replacing fire between 200 and 750 years ago, although many sites exhibited evidence of moderate‐severity fire that created multi‐aged stands. More than two‐thirds of sites experienced multiple non‐stand‐replacing fires following stand initiation. A spatial generalized linear mixed model demonstrated that historical fire occurrence was negatively associated with average snow disappearance day and time since last fire and positively associated with drought. Significant variability in the number of fires, length of fire return intervals, and sample depth across sites made calculation of informative mean fire return intervals (MFRIs) difficult. Site‐level annual probability of fire from our mixed model ranged from 0.039 to 0.003, equivalent to MFRIs of 26–389 years. We used fire and tree establishment records to infer the general location of several large historical fire events that likely burned as much or more area as the >50,000 ha fires that burned across our study region in 2020. We also identified periods of extensive burning and subsequent tree establishment that occurred across seven centuries within six large river drainages that made up our study region. Although tree establishment occurred for up to a century following stand‐replacing fire at some sites, we show that these apparent long periods of establishment were relatively short pulses of regeneration separated by reburns. This study demonstrates that many highly productive Douglas‐fir‐dominated stands in western Oregon are significantly departed from historical fire disturbance regimes. Management that emphasizes rapid re‐establishment of closed canopy forest conditions following fire and development of old‐growth forest conditions in the absence of fire may fail to provide for the unique and highly valued ecosystem services associated with these forests.
Journal Article