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Causes of Species Declines
Effects of Insecticides and Agricultural Practices on Migratory Shorebirds in the Prairie Pothole Region
Many shorebirds in North America use agricultural areas in the Prairie Pothole Region of the northern Great Plains to refuel during critical migratory stopovers, but rapid increases in neonicotinoid insecticide use in agricultural fields may pose risks to their ability to efficiently refuel and migrate. Neonicotinoids can suppress appetite, lower refueling rates, and cause rapid mass and fat loss. Additionally, neonicotinoids may reduce invertebrate populations, further diminishing the quality of agricultural wetlands for shorebirds. This project quantifies agricultural impacts on abundance, body condition, and prey biomass for migratory shorebirds in the Prairie Pothole Region. Goals of the project are: 1) to quantify the effects of neonicotinoid insecticides on shorebird physiology and invertebrate biomass, and 2) to assess habitat use and quality of agricultural wetlands used by migratory shorebirds. Across two spring and two fall migration seasons in 2021-2023, we collected plasma samples from shorebirds (n = 182; 11 species) and water samples from wetlands (n = 84) to better understand neonicotinoid exposure. We also conducted wetland (n = 84), macroinvertebrate (n = 48), and road transect surveys (n > 100) to better inform wetland quality and shorebird use. Our research provides a foundation for understanding how insecticides and agricultural practices impact shorebird physiology, wetland use, and prey biomass. Our findings will provide managers with results to potentially invoke changes in management practices (e.g., flooding fields) and farming policies.
Shelby McCahon
Effect of Selenium Accumulation on Yuma Ridgway’s Rails at the Salton Sea, California
Emergent marshes around the Salton Sea, California support one of the largest populations of the federally endangered Yuma Ridgway’s rails in the United States. Much of the rail habitat in the region is managed by state and federal agencies, but non-planned marshes have appeared recently at agricultural drainage outlets around the Salton Sea. These unplanned marshes originate from agricultural drainage water with varying concentrations of selenium, whereas the marshes managed by state and federal agencies receive Colorado River water with relatively low concentrations of selenium. Elevated selenium causes embryo malformations, and, hence, these unplanned marshes may be ecological traps for these endangered rails. We documented selenium burdens in breeding rails and selenium concentrations in rail prey items within marshes fed by different water sources to assess whether high selenium in unplanned marshes pose risks to Yuma Ridgway’s rails. During 2020-2023, we captured 218 rails in 12 marshes around the Salton Sea. We attached GPS transmitters to 96 adult rails and located 78 nests. We collected blood, feathers, egg samples from nests, and samples of common rail prey species. Selenium concentration in rail blood was higher in unplanned marshes than in state/federal managed marshes, whereas selenium concentration in rail feathers did not differ between the two marsh types. We collected 71 eggshell samples and 12 whole eggs from 56 of the 78 nests across the 4 years. We collected 713 rail prey samples (i.e., crayfish, mosquitofish) from 181 rail home ranges, 205 irrigation inflows and outflows, and 81 other sampling locations in 12 marshes. Selenium concentration of rail prey was higher in unplanned marshes compared to those managed by state/federal agencies.
Cydney Yost
Nesting success and recruitment of western grebes in Idaho
We compiled data summarizing the status of current and historical grebe populations on 770 breeding lakes across North America. The largest concentrations of adult grebes (>1000) during the breeding season were concentrated in only 5% of the breeding lakes used by grebes and most (73%) of the 770 breeding lakes supported only small numbers of breeding adults (<100). We developed this breeding lake inventory into an interactive website in partnership with the Center for Digital inquiry and Learning (CDIL) at the University of Idaho and that website will launch in early 2024. Cascade Reservoir supports the largest grebe breeding colony in Idaho. At Cascade Reservoir, we used drones to document the cause of early nest abandonment that we had observed in 2020 and 2021. We reconstructed nest histories and estimated nest fate for >3800 nests based on repeated flights and drone imagery. We estimated nest survival and examined the effects of environmental variables on nest fate. Our results indicate that daily peak wind direction, daily peak wind speed, daily precipitation, daily water level, and date influence nest fate. Daily nest survival decreased as the nesting season progressed and was also low on days when precipitation combined with winds blew into the colony. Our interactive website and research on the factors that affect nest survival will help managers implement actions that can potentially increase grebe recruitment in Idaho and elsewhere. Anne Yen defended her thesis in Dec 2023 and is graduating Spring 2024.
Anne Yen
Grouse & Grazing: effects of cattle grazing on greater sage-grouse
Despite many studies of greater sage-grouse (Centrocercus urophasianus) habitat requirements, we know surprisingly little about the effects of livestock grazing on sage-grouse populations. As a result, various groups make claims about the presumed effects of livestock grazing on sage-grouse, and litigation over this issue is common. We brought together a multi-partner team to develop and implement a 10-year study with replicated experimental grazing treatments to evaluate the effects of grazing on demographic traits and habitat characteristics of sage-grouse. The results will help guide management actions (and inform policy and litigation decisions) throughout southern Idaho and throughout the species’ range. In 2023, we completed our 10th and final year of data collection for the study. Over the course of the project, we attached transmitters to 1,343 sage-grouse hens and located and monitored 1,216 nests of those radio-marked hens. We have also measured vegetation characteristics at those nests and 3,196 random plots within 21 grazing treatment pastures. In addition, we have also collected 12,446 insect pitfall samples, 6,334 insect sweep net samples, and measured grazing intensity within those same 21 treatment pastures.
Effects of climate, population density, body condition, and competitors on survival and foraging behavior of northern Idaho ground squirrels
The northern Idaho ground squirrel is a federally threatened species endemic to a 1600-km2 area in Idaho. Fewer than 3,000 squirrels persist in a fragmented metapopulation such that the species now occupies 0.5% of its historic range. Hence, it is imperative that we understand the selection pressures influencing foraging habits and survival of these rare squirrels so that managers can recover the species. We captured and marked 1689 northern Idaho ground squirrels from 2013-2021 for survival analyses and attached 92 geolocators to adult northern Idaho ground squirrels from 2017-2020 to document above-ground foraging activity. We then used statistical models to assess the effects of hibernation, endogenous state, density, and weather on above-ground foraging activity and seasonal survival of northern Idaho ground squirrels. Females had higher survival than males and adults had higher survival than juveniles. Daily survival was greater during hibernation than during the active season. Survival was also density-dependent and negatively associated with Columbian ground squirrel density and total winter snowfall. Foraging activity increased throughout the active season, more so for lean squirrels compared to heavy squirrels. Foraging activity was positively associated with conspecific density and negatively associated with extreme (hot and cold) temperatures. These results suggest management actions that improve forage are likely to promote northern Idaho ground squirrel survival and so populations, though only in areas where Columbian ground squirrels don’t exclude threatened species.
Austin Allison
Effectiveness of habitat restoration as a recovery tool for northern Idaho ground squirrels
The northern Idaho ground squirrel is a federally threatened species endemic to west-central Idaho. Squirrel populations are fragmented such that the species currently occupies <1% of its historic range. Habitat loss resulting from anthropogenic fire suppression is the leading hypothesis to explain past population declines and fragmentation. We are using a before-after-control-impact design to experimentally evaluate the effectiveness of habitat restoration treatments – forest thinning and prescribed burning adjacent to patches occupied by squirrels and prescribed burning within patches occupied by squirrels – as potential tools to recover the species. This project was initiated in 2014 and assessment of experimental restoration treatments are ongoing. Over the past 10 years, we have marked 2087 individual squirrels for survival analyses and attached 349 radio-collars and 263 geolocators to squirrels to document foraging, habitat selection, and hibernation behavior at 13 study sites. We also collected ~1900 fecal pellet samples from captured squirrels for diet analysis and collected detailed vegetation structure and composition data to assess forage availability and habitat quality. Amanda Goldberg completed her dissertation in 2018, Austin Allison completed his thesis in 2022, and Alice Morris began her thesis work in 2021. To date, we have published 14 papers in peer-reviewed journals from this project.
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
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
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