Movement Ecology


Barn Owl Movement and Rodenticide Exposure in Industrial Agriculture

Project Lead: Ryan Bourbour

Barn Owls (Tyto alba) are incredible hunters: a single nest can consume thousands of pest rodents. For this reason, they are an effective component of an Integrative Pest Management program in agriculture, open spaces, and even urban areas. However, anticoagulant rodenticides are often applied to the landscape in conjunction with recruiting Barn Owls via artificial nest boxes to control rodent pests.


Ultimately, lethal and sub-lethal secondary poisoning from rodenticides can diminish the ecosystem services provided by Barn Owls, among other negative effects. We currently have little understanding of how often living Barn Owls in California are exposed to rodenticides and what effect this exposure has on hunting behavior and reproductive success. To gain a clearer picture of the relationship between Barn Owls and rodenticide applications, we will be using GPS-technology to track hunting and movement patterns across an industrial agricultural landscape where we will identify locations that Barn Owls may be capturing prey that have fed at rodenticide bait stations.


Our main objective is to map the hunting locations of Barn Owls across multiple crop and habitat types in relation to rodenticide bait stations and rodenticide exposure of growing chicks being provisioned at the nest. This information will allow farmers to plan rodenticide applications in the future to avoid placing baits in areas Barn Owls prefer to hunt while simultaneously targeting areas where Barn Owls are not providing effective pest control services. This will be the first study to describe hunting behavior around rodenticide bait stations and relating it to rodenticide exposure in both nestlings and adults.



Reproductive and Movement Ecology of Northern Harriers

Project Lead:  Shannon Skalos

The Northern Harrier (Circus hudsonius) is a widespread raptor species that breeds and forages in marshes, associated grasslands and agricultural fields. Prey varies seasonally and geographically from rodents to passerines to waterfowl. In California, local breeding populations have experienced steady declines, and as a result, harriers are listed as a Species of Special Concern by the California Department of Fish and Wildlife. Suisun Marsh once had one of the largest breeding populations of harriers in the state, but the current breeding population is small. In collaboration with the USGS, we are studying the reproductive, foraging and movement ecology of harriers in Suisun Marsh using a variety of field and telemetry techniques to determine effects of prey and habitat selection on harrier population demographics and behavior. To better understand harrier ecology and inform their management, it is imperative that we investigate not only breeding ecology of harriers in Suisun, but also movement, habitat selection and interactions with prey species across the four major phases of their annual cycle (breeding, fall migration, wintering, spring migration), both in Suisun and across their range. As such, this research aims to address to following objectives: 1) determine how prey influences reproductive success and provisioning to nestlings, 2) examine nest site characteristics and habitat selection across different spatial scales, and 3) examine movement and site fidelity across different temporal scales and age-classes.


Additionally, because Suisun Marsh is an important breeding area for waterfowl, and harriers breed concurrently with waterfowl in upland habitats, we will study the potential impacts of harrier foraging on waterfowl reproductive success. We will also study reproductive success, foraging and movement ecology of Red-tailed Hawks (Buteo jamaicensis), Great Horned Owls (Bubo virginianus) and Common Ravens (Corvus corax), three species nesting in Suisun Marsh and identified as potential avian predators effecting waterfowl reproductive success. The results of this research will add to our understanding of avian predator behavior and population biology, as well as predator-prey interactions between avian predators and breeding waterfowl in California.

Migration Ecology of Golden-crowned Sparrows

Project Lead: Autumn Iverson

Seventy percent of temperate-zone migrating songbirds have shown widespread decline in western North America over the last few decades. Along migration routes, songbirds face many threats such as navigational challenges, a changing predator assemblage, and shifting resources. They also face human related threats such as habitat loss and land-use changes. Due to the speed of these landscape changes, it is thought that songbirds are unlikely to evolve genetic adaptations that can keep pace.  Most research on migratory birds has occurred during the breeding season and migration is the least understood life history stage. Therefore, delineating migration paths as well as habitat quality and threats along those paths are critical research needs, especially on wide landscape scales. 


For seasonal passerine migrants, understanding how important the limiting factors experienced during migration are to the full life-cycle requires knowledge on different fronts, including how populations are connected between breeding and wintering ranges, how they utilize and choose stopovers during migration, and how climate changes in disparate home ranges may be affecting population numbers.


Golden-crowned Sparrows (Zonotrichia atricapilla; GCSP) breed in northern latitudes of North America such as Alaska, British Columbia and the Yukon, and winter along the west coast from British Columbia south to Baja California. The GCSP is considered a long-distance migrant with the entire population migrating seasonally between these locations. Although GCSP populations are not currently considered at risk, there is some indication that the species may be experiencing range shifts due to climate change.

This research will investigate migration in a temperate-zone migrating songbird, the Golden-crowned Sparrow, by estimating migratory connectivity across the wintering range using stable isotope analysis, determining drivers for stopover locations using new miniaturized GPS technology, and investigating the effects of climate on annual population trends using Christmas Bird Count data.