Migration, Hibernation, and Movement Ecology
Post-breeding Movements, Migration Resource Selection, and Survival of Burrowing Owls
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Western burrowing owls (Athene cunicularia hypugaea) are declining or have disappeared from many portions of their historic breeding range. The decline of burrowing owl populations is often attributed to conversion of native grasslands to agriculture and urban development, and to declines in abundance of burrowing mammals that the owls rely on for creation of nest burrows. Burrowing owls are relatively well studied during the breeding season but relatively little is known about their ecology after breeding. Some burrowing owls move to a distinct post-breeding home range before they migrate (post-breeding movement) where they spend approximately 2.5 months of their annual cycle. We have been working with numerous cooperators to attach satellite transmitters to 280 burrowing owls in the U.S. and Canada over the past 11 years which enables us document movements and resource selection of burrowing owls after they leave the breeding grounds. The transmitters also allow us to document daily survival probabilities across the owl’s annual cycle. The objectives of this project are: 1) thoroughly describe post-breeding movements of migrating burrowing owls, 2) investigate why some burrowing owls make a post-breeding movement prior to migration while others do not, 3) document resources burrowing owls select during migration, and 4) identify factors that influence survival. The results of this project will help ensure that management efforts that target burrowing owls do not neglect to consider post-breeding and migration life stages where knowledge is currently lacking.
Anthony Locatelli
Seasonal movements, population connectivity, and survival of
light-footed Ridgway’s Rails
Light-footed Ridgway’s rails (Rallus obsoletus levipes) are federally endangered and they inhabit coastal wetlands within a restricted geographic range that spans the U.S.-Mexico border. These rare birds persist in a highly urbanized landscape where an estimated 70% of historic wetlands have been lost. The wetlands that remain are fragmented and threatened by continued habitat degradation. Despite their rarity, very little is known about their survival, habitat selection, and connectivity among occupied marshes. Moreover, captive bred light-footed Ridgway’s rails are released annually as part of species recovery efforts, but the effectiveness of the captive-breeding program to augment the wild population and the post-release survival and movement of captive-bred rails has never been assessed. We attached satellite transmitters to 48 captive-bred and 42 wild-caught rails to compare survival and habitat selection between wild and captive-bred rails. We collected >8,000 rail locations over 3 years and at 3 study sites to use in our analysis. This information can be used to identify management actions and help improve the captive breeding program and increase survival of captive-raised rails in the wild. Our research will improve our understanding of light-footed Ridgway’s rail demography and enhance the efficacy of current recovery efforts.
Kim Sawyer
Ecological Pressures Governing Hibernation Habitat Selection in Northern Idaho Ground Squirrels
Northern Idaho ground squirrel populations declined in the 20th century such that the species now occupies <1% of its historic range. Habitat loss and fragmentation due to anthropogenic fire suppression is the leading hypothesis to explain this decline, with current management actions focused on forest thinning and prescribed burning to try to recover the species. These management actions focus on creating open-canopy active-season habitat for squirrels. However, many northern Idaho ground squirrels move away from active-season ranges to hibernate, often selecting hibernaculum sites in forests. The underlying ecological pressures driving hibernation site selection are presently unknown but managers need to incorporate habitat needs during hibernation into forest management plans. Competition with the sympatric Columbian ground squirrel, predation avoidance, and selection for an optimal thermal environment are among the hypotheses we are testing to explain squirrel hibernation site selection. To test these alternative hypotheses, this project is: (1) attaching radio-collars and geolocators to squirrels to document hibernation timing and habitat selection, (2) deploying trail cameras to document badger predation of hibernating squirrels, and (3) trapping Columbian ground squirrels to estimate population size and habitat use. This research will provide a more comprehensive understanding of the full breadth of habitat these squirrels require, which can inform management and recovery efforts of this rare species.
Alice Morris
Geographic clutch size variation in squamates: a comparative approach
For many terrestrial vertebrates, clutch size is positively correlated with latitude, with animals producing more offspring per reproductive attempt at larger absolute latitudes. More than seventy years of avian and mammalian research has produced three hypotheses to explain this trend, but the highly mobile nature of most endotherms has confounded previous attempts to identify the causative mechanism. We are implementing the hypothetico-deductive method within a phylogenetic framework to test explicit predictions on more than 1,000 species of extant snake, while simultaneously conducting an intra-specific study focused on one of the west's most charismatic snakes: the western rattlesnake. We have collected clutch size data for more than 60 gravid female rattlesnakes at field sites and museums range-wide since commencing our fieldwork in 2023. This work will continue into 2024, where the project will expand to assess seasonal movement variation in prairie rattlesnakes in response to human disturbance, habitation, and roads. Our fieldwork will be combined with existing data to create a complete picture of geographic clutch size variation range-wide in these species, which will allow us to 1) quantify the role of intraspecific plasticity in latitudinal clutch size variation 2) identify the mechanisms responsible for intraspecific clutch size variation and 3) improve our understanding of the risks faced by one of North America's most widespread snakes. Overall, this project will improve our understanding of life history evolution in vertebrates and will contribute novel findings to numerous disciplines including life history evolution, herpetology, and conservation biology.
Emily Martin
Causes of differential migration in birds: test of hypotheses in the rough-legged hawk
Seasonal migration occurs in animals of all taxa, but we know surprisingly little about why individuals migrate. For example, many birds have differential migration whereby one sex migrates further than the other, and the causes of sex-specific migration behavior is a topic of debate. Recent advances in remote-tracking technologies have greatly enhanced our ability to collect large amounts of fine-scale data on long-distance avian migration behavior. The Rough-legged Hawk (Buteo lagopus) breeds throughout arctic and subarctic regions of North America and winters throughout the coterminous United States, with no spatial overlap between breeding and wintering areas. Since 2014, we have attached satellite or GPS transmitters to over 190 Rough-legged Hawks to document their migration behavior. We trapped and deployed transmitters on hawks on the wintering grounds, the breeding grounds, and during migration. Many of these transmitters are still generating data, and we continued to deploy additional units with 12 transmitters deployed throughout the United States and Canada during the 2023-24 winter. This dataset will provide a foundation allowing us to test a suite of hypotheses proposed to explain why Rough-legged Hawks exhibit differential migration.
Neil Paprocki