Winter Use of a Highly Diverse Suite of Habitats by Irruptive Snowy Owls

Therrien, Jean‐François; Weidensaul, Scott; Brinker, D.J.; Huy, Steve; Miller, Trish; Jacobs, Eugene A.; Weber, D. J.; Mcdonald, Tom; Lanzone, Mike; Smith, Norman E.; Lecomte, Nicolas

doi:10.1656/045.024.s712

Cited by 10 publications

(3 citation statements)

References 13 publications

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“…Such high-risk habitats in human-dominated areas, which also include overhead power lines, highways and roads, may not be recognized by inexperienced immature owls when they arrive on the wintering grounds. Therrien et al (2017) reported age-related differences in habitat types used by snowy owls in eastern North America, and found that juvenile owls wintered in developed areas more than adults, suggesting the potential for increased exposure to contaminants (Miller et al 2015) and human disturbance. Interestingly, other studies of migratory birds have reported that mortality rates of immatures and adults do not differ much once immatures have survived a period of high risk immediately post-fledging such as the initial migration (e.g.…”

Section: Discussionmentioning

confidence: 99%

Density-dependent winter survival of immatures in an irruptive raptor with pulsed breeding

et al. 2021

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Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption years. This could occur if subordinate individuals (mainly immatures) are forced into suboptimal habitats due to density-dependent effects in irruption years. To test whether irruptive individuals had lower survival than non-irruptive ones, we combined necropsy results (N = 365) with telemetry (N = 185) from more than 20 years to record timing and causes of mortality in snowy owls (Bubo scandiacus), which irrupt into eastern North America during winter following high breeding output caused by lemming peaks in the Arctic. Mortality was more than four times higher in irruption years than non-irruption years, but only for immatures, and occurred disproportionately in early winter for immatures, but not adults. Mortality was also higher in eastern North America, where owl abundance fluctuates considerably between years, compared to core winter regions of the Arctic and Prairies where populations are more stable. Most mortality was not due to starvation, but rather associated with human activity, especially vehicle collisions. We conclude that immature snowy owls that irrupt into eastern North America are limited by density-dependent factors, such as increased competition forcing individuals to occupy risky human-altered habitats. For highly mobile, irruptive animals, resource pulses may have a limited impact on population dynamics due to low subsequent survival of breeding output during the nonbreeding season.

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Section: Discussionmentioning

confidence: 99%

Density-dependent winter survival of immatures in an irruptive raptor with pulsed breeding

et al. 2021

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“…During the non-breeding season, individuals regularly overwinter in the Canadian Prairies and the American Great Plains (Chang & Wiebe 2018), and throughout the entire temperate regions of North America during irruption years (Kerlinger & Lein 1988, Robillard et al . 2016, Therrien et al . 2017, Holt et al .…”

Section: Introductionmentioning

confidence: 99%

Long-term population decline of a genetically homogenous continental-wide top Arctic predator

Gousy-Leblanc

Therrien

Broquet

et al. 2022

Preprint

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Genetic analysis can provide valuable information for conservation programs by unraveling the demographic trajectory of populations, by estimating effective population size, or by inferring genetic differentiation between populations. Here, we investigated the genetic differentiation within the Snowy Owl (Bubo scandiacus), a species identified as vulnerable by the IUCN, to (i) quantify connectivity among wintering areas, (ii) to evaluate current genetic diversity and effective population size and (iii) to infer changes in the historical effective population size changes from the last millennia to the recent past. The Snowy Owl, a highly mobile top predator, breeds across the Arctic tundra which is a region especially sensitive to current climate change. Using SNP-based analyses on Snowy Owls sampled across the North American nonbreeding range, we found an absence of genetic differentiation among individuals located up to 4,650 km apart. Our results suggest high genetic intermixing and effective dispersal at the continental scale despite documented philopatry to nonbreeding sites in winter. Reconstructing the population demographic indicated that North American Snowy Owls have been steadily declining since the Last Glacial Maximum ca 20,000 years ago and concurrently with global increases in temperature. Conservation programs should now consider North American Snowy Owls as a single, genetically homogenous continental-wide population which is most likely sensitive to the long-term global warming occurring since the Last Glacial Maximum.

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“…During irregular irruptive movements south, Snowy Owls use a diversity of urban, rural, coastal, and marine habitats (Therrien et al. ) whereas those that regularly winter south of their breeding range primarily use flat open prairie (Kerlinger et al. ).…”

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Habitat selection by wintering male and female Snowy Owls on the Canadian prairies in relation to prey abundance and a competitor, the Great Horned Owl

Chang

Wiebe

2018

J. Field Ornithol.

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Birds overwintering at high latitudes may find it challenging to meet their energy budgets when thermoregulatory costs are high and food availability is low. Snowy Owls (Bubo scandiacus), like most raptors, exhibit reversed sexual size dimorphism, so, if availability of high-quality (food-rich) habitats is limited, we predicted that larger and dominant females would use better-quality habitat than males. During the winters of 2014-2015 and 2015-2016 in Saskatchewan, where many Snowy Owls overwinter annually, we measured prey (small mammal) abundance in fields with four types of cover, including cut stalks (stubble) of canola, grain and legume crops, and pasture, and related this estimate of quality to habitat selection by males and females. Small mammal abundance varied annually, but not among the three types of crop stubble. However, prey were less abundant in pastures than in the three types of crop cover in one of three years. Biweekly surveys of owls conducted during the two winters along a 60-km transect revealed weak selection for legume fields, especially by males. The home ranges of nine females with transmitters included proportionally less canola stubble than those of eight males with transmitters. Within home ranges, males avoided canola stubble and tended to use legume fields more, whereas females used all four habitat types in proportion to availability. Fewer Snowy Owls than expected were observed at locations along the transect within 800 m of Great Horned Owls (Bubo virginianus) and their associated habitats, suggesting that Snowy Owls also avoided these potential competitors on the landscape. Our results suggest that larger females outcompete smaller male Snowy Owls for home ranges in preferred habitat with less canola stubble because stubble-free legume fields provide easier access to prey than canola fields with numerous rigid stalks.RESUMEN. Selecci on de h abitat durante el invierno por hembras y machos de Bubo scandiacus en las praderas canadienses en relaci on con la abundancia de presas y un competidor, Bubo virginianus A las aves que pasan el invierno en latitudes altas les puede resultar dif ıcil cumplir con sus presupuestos de energ ıa cuando los costos de termorregulaci on son altos y la disponibilidad de alimentos es baja. Bubo scandiacus, como la mayor ıa de las aves de rapiña, exhibe un dimorfismo invertido en el tamaño sexual, por lo tanto, si la disponibilidad de h abitats de alta calidad (ricos en alimentos) es limitada, predecimos que las hembras m as grandes y dominantes usar ıan el h abitat de mejor calidad en comparaci on con los machos. Durante los inviernos de 2014-2015 y 2015-2016 en Saskatchewan, donde muchos B. scandiacus pasan el invierno anualmente, medimos la abundancia de presas (mam ıferos pequeños) en campos con cuatro tipos de cobertura, incluidos tallos cortados (rastrojos) de cultivos de canola, cereales y legumbres, y pasto, y se relacion o esta estimaci on de calidad para la selecci on de h abitat por parte de machos y hembras. La abundancia de mam ıferos peq...

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Winter Use of a Highly Diverse Suite of Habitats by Irruptive Snowy Owls

Cited by 10 publications

References 13 publications

Density-dependent winter survival of immatures in an irruptive raptor with pulsed breeding

Density-dependent winter survival of immatures in an irruptive raptor with pulsed breeding

Long-term population decline of a genetically homogenous continental-wide top Arctic predator

Habitat selection by wintering male and female Snowy Owls on the Canadian prairies in relation to prey abundance and a competitor, the Great Horned Owl

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