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Seasonal Effects of Habitat on Sources and Rates of Snowshoe Hare Predation in Alaskan Boreal Forests.

Feierabend D, Kielland K - PLoS ONE (2015)

Bottom Line: We compared the models using Akaike's information criterion with correction for small sample size.Because hares rely on vegetative cover for concealment from predators, we measured cover in predation sites and habitats that the hares occupied and concluded that habitat type had a greater influence on the sources of predation than the amount of cover in any given location within a habitat.Our observations illustrate the vulnerability of hares to predators in even the densest coniferous habitat available in the boreal forest, and indicate strong seasonal changes in the rates and sources of predation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.

ABSTRACT
Survival and predation of snowshoe hares (Lepus americanus) has been widely studied, yet there has been little quantification of the changes in vulnerability of hares to specific predators that may result from seasonal changes in vegetation and cover. We investigated survival and causes of mortalities of snowshoe hares during the late increase, peak, and decline of a population in interior Alaska. From June 2008 to May 2012, we radio-tagged 288 adult and older juvenile hares in early successional and black spruce (Picea mariana) forests and, using known-fate methods in program MARK, evaluated 85 survival models that included variables for sex, age, and body condition of hares, as well as trapping site, month, season, year, snowfall, snow depth, and air temperature. We compared the models using Akaike's information criterion with correction for small sample size. Model results indicated that month, capture site, and body condition were the most important variables in explaining survival rates. Survival was highest in July, and more generally during summer, when alternative prey was available to predators of hares. Low survival rates coincided with molting periods, breeding activity in the spring, and the introduction of juveniles to the sample population in the fall. We identified predation as the cause of mortality in 86% of hare deaths. When the source of predation could be determined, hares were killed more often by goshawks (Accipiter gentilis) than other predators in early successional forest (30%), and more often by lynx (Lynx canadensis) than other predators in black spruce forest (31%). Great horned owls (Bubo virginianus) and coyotes (Canis latrans) represented smaller proportions of hare predation, and non-predatory causes were a minor source (3%) of mortality. Because hares rely on vegetative cover for concealment from predators, we measured cover in predation sites and habitats that the hares occupied and concluded that habitat type had a greater influence on the sources of predation than the amount of cover in any given location within a habitat. Our observations illustrate the vulnerability of hares to predators in even the densest coniferous habitat available in the boreal forest, and indicate strong seasonal changes in the rates and sources of predation.

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Trapping sites and VHF collar recovery locations for snowshoe hares.Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Figure includes data previously published in Feierabend and Kielland [16].
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pone.0143543.g001: Trapping sites and VHF collar recovery locations for snowshoe hares.Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Figure includes data previously published in Feierabend and Kielland [16].

Mentions: This study took place in the Bonanza Creek Experimental Forest (64° N, 148° W), located approximately 20 km southwest of Fairbanks, Alaska (Fig 1). This area consists of a mosaic of floodplain, lowland, and upland vegetation types that include early successional forest, balsam poplar (Populus balsamifera), white spruce (Picea glauca), black spruce, muskeg, wetland, mixed forest, shrub birch (Betula spp.), Alaska birch (Betula neoalaskana), aspen (Populus tremuloides), and recently burned communities. Snowshoe hare population dynamics have been monitored here since 1998 [32]. We used established trapping grids in two representative snowshoe hare habitats (hereafter referred to as “Deciduous” and “Conifer”) with populations sufficiently large for estimating hare densities and survival. The Deciduous grid was in an early successional community dominated by willow (Salix spp.), thin-leaf alder (Alnus tenuifolia), and balsam poplar, located adjacent to the Tanana River. Understory species included Epilobium angustifolium, Cornus canadensis, Calamagrostis canadensis, and Equisetum spp. The Conifer grid was in a mature black spruce community with an understory composed of Ledum spp., Rosa acicularis, Vaccinium vitis-idaea, Salix spp., Chamaedaphne calyculata, mosses, and lichens. Each trapping grid was 9 ha in size with 50 traps arranged on 10 transects (5 traps/transect) in a rectangular pattern with 50 m between traps. The two trapping grids were separated by 1.5 km of poor hare habitat (e.g., open muskeg, wetland). No hares were observed moving between grids during 12 years of population monitoring. However, it was not uncommon for study hares to move up to 1 km from the trapping grids and we observed 5 hares moving more than 5 km from their respective capture sites [16].


Seasonal Effects of Habitat on Sources and Rates of Snowshoe Hare Predation in Alaskan Boreal Forests.

Feierabend D, Kielland K - PLoS ONE (2015)

Trapping sites and VHF collar recovery locations for snowshoe hares.Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Figure includes data previously published in Feierabend and Kielland [16].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696674&req=5

pone.0143543.g001: Trapping sites and VHF collar recovery locations for snowshoe hares.Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Figure includes data previously published in Feierabend and Kielland [16].
Mentions: This study took place in the Bonanza Creek Experimental Forest (64° N, 148° W), located approximately 20 km southwest of Fairbanks, Alaska (Fig 1). This area consists of a mosaic of floodplain, lowland, and upland vegetation types that include early successional forest, balsam poplar (Populus balsamifera), white spruce (Picea glauca), black spruce, muskeg, wetland, mixed forest, shrub birch (Betula spp.), Alaska birch (Betula neoalaskana), aspen (Populus tremuloides), and recently burned communities. Snowshoe hare population dynamics have been monitored here since 1998 [32]. We used established trapping grids in two representative snowshoe hare habitats (hereafter referred to as “Deciduous” and “Conifer”) with populations sufficiently large for estimating hare densities and survival. The Deciduous grid was in an early successional community dominated by willow (Salix spp.), thin-leaf alder (Alnus tenuifolia), and balsam poplar, located adjacent to the Tanana River. Understory species included Epilobium angustifolium, Cornus canadensis, Calamagrostis canadensis, and Equisetum spp. The Conifer grid was in a mature black spruce community with an understory composed of Ledum spp., Rosa acicularis, Vaccinium vitis-idaea, Salix spp., Chamaedaphne calyculata, mosses, and lichens. Each trapping grid was 9 ha in size with 50 traps arranged on 10 transects (5 traps/transect) in a rectangular pattern with 50 m between traps. The two trapping grids were separated by 1.5 km of poor hare habitat (e.g., open muskeg, wetland). No hares were observed moving between grids during 12 years of population monitoring. However, it was not uncommon for study hares to move up to 1 km from the trapping grids and we observed 5 hares moving more than 5 km from their respective capture sites [16].

Bottom Line: We compared the models using Akaike's information criterion with correction for small sample size.Because hares rely on vegetative cover for concealment from predators, we measured cover in predation sites and habitats that the hares occupied and concluded that habitat type had a greater influence on the sources of predation than the amount of cover in any given location within a habitat.Our observations illustrate the vulnerability of hares to predators in even the densest coniferous habitat available in the boreal forest, and indicate strong seasonal changes in the rates and sources of predation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.

ABSTRACT
Survival and predation of snowshoe hares (Lepus americanus) has been widely studied, yet there has been little quantification of the changes in vulnerability of hares to specific predators that may result from seasonal changes in vegetation and cover. We investigated survival and causes of mortalities of snowshoe hares during the late increase, peak, and decline of a population in interior Alaska. From June 2008 to May 2012, we radio-tagged 288 adult and older juvenile hares in early successional and black spruce (Picea mariana) forests and, using known-fate methods in program MARK, evaluated 85 survival models that included variables for sex, age, and body condition of hares, as well as trapping site, month, season, year, snowfall, snow depth, and air temperature. We compared the models using Akaike's information criterion with correction for small sample size. Model results indicated that month, capture site, and body condition were the most important variables in explaining survival rates. Survival was highest in July, and more generally during summer, when alternative prey was available to predators of hares. Low survival rates coincided with molting periods, breeding activity in the spring, and the introduction of juveniles to the sample population in the fall. We identified predation as the cause of mortality in 86% of hare deaths. When the source of predation could be determined, hares were killed more often by goshawks (Accipiter gentilis) than other predators in early successional forest (30%), and more often by lynx (Lynx canadensis) than other predators in black spruce forest (31%). Great horned owls (Bubo virginianus) and coyotes (Canis latrans) represented smaller proportions of hare predation, and non-predatory causes were a minor source (3%) of mortality. Because hares rely on vegetative cover for concealment from predators, we measured cover in predation sites and habitats that the hares occupied and concluded that habitat type had a greater influence on the sources of predation than the amount of cover in any given location within a habitat. Our observations illustrate the vulnerability of hares to predators in even the densest coniferous habitat available in the boreal forest, and indicate strong seasonal changes in the rates and sources of predation.

Show MeSH
Related in: MedlinePlus