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Current Research

Breeding Biology and Population Dynamics of Yellow-billed Cuckoos

The Yellow-billed Cuckoo (Coccyzus americanus) is a neotropical migrant that historically bred in riparian habitats throughout much of North America. Since the late 1800's many of the forests that cuckoos depended upon, particularly in the West, have been destroyed or degraded by human activity. As a result, both the range and numbers of breeding cuckoos have decreased dramatically and the western subspecies is currently a candidate for Federal Endangered Species status. Our research focuses on documenting the reproductive biology of this poorly known species and developing survey techniques that reliably estimate numbers of breeding birds in an area. We conduct our cuckoo research on the Lower Colorado River and in the Kern River Valley

Breeding Biology and Population Dynamics of Southwestern Willow Flycatchers

We have monitored a population of endangered Southwestern Willow Flycatchers (Empidonax traillii extimus) on the South Fork Kern River since 1989. We have been particularly interested in understanding the consequences of Brown-headed Cowbird (Molothrus ater) parasitism for flycatcher reproductive success and population dynamics. Despite control efforts that have effectively reduced parasitism rates and increased reproductive success, the Southwestern Willow Flycatcher population in the Kern River Valley has yet to increase in size. We are currently investigating the roles that habitat quality, food abundance, and geographic isolation play in limiting population growth.

Distribution and Ecology of Wintering Willow Flycatchers

We are increasingly interested in the distribution and ecology of wintering Willow Flycatchers. We have traveled to Central America (Costa Rica, Panama, El Salvador, Guatemala, and Mexico) and parts of South America (Ecuador) to determine whether Willow Flycatchers are present in areas where, historically, they were known to winter. On these trips, we capture birds and mark them with bands to estimate survival and winter site fidelity between years. In collaboration with other researchers, we collect small samples of DNA to determine the sex and subspecies of captured individuals and pluck single feathers for stable isotope analysis that will allow us to link wintering and breeding populations of flycatchers.

Management Efforts

Removal of Non-native Vegetation

Each year we survey the South Fork Kern River for non-native plant species such as Purple Loosestrife, Salt Cedar, and Russian Olive. These invasive species can dramatically alter the hydrology of wetlands and riparian areas and destroy specialized ecological interactions among native species if left unchecked.