My studies have focused on how Neotropical Migrants - birds which breed in North America and spend their winters in Central and South America - use this study site during migration. This site represents a small remnant island of riparian habitat surrounded by urban and agricultural development. I am looking at how these birds use these "ribbons of green" as resting and refueling sites during their long migrations.

Riparian systems are considered one of the most productive forms of wildlife habitat in North America, especially in the arid western United States. The term riparian forest is applied to the broad-leaved and winter deciduous tree formations that line water courses. Large numbers of birds, including Orange-crowned Warblers (Vermivora celata), Western Flycatchers (Empidonax difficilis), Wilson's Warblers (Wilsonia pusilla), and Yellow Warblers (Dendroica petechia), forage and take shelter in riparian forest habitat during their migratory journeys and during the breeding season. In the arid southwest riparian plant communities appear to be particularly important to migrating birds because they remain productive during late summer post-breeding dispersal and fall migration in contrast to the dry upland habitats.

The extensive riparian forests which historically encompassed several million acres in California have been reduced to mere remnants within the last 100 years. For example, instead of a strip measurable in miles, the forested zones along Sacramento Valley streams are now often very narrow and discontinuous. This situation has become typical of most riparian systems in California, some researchers estimate that 90-97% of these riparian areas have been lost. The creeks in the southern San Francisco Bay Region have suffered similar degradation, primarily due to heavy urban development and agriculture.

The loss of this riparian habitat has been implicated in the reduction of breeding birds. For example, the numbers of breeding pairs of Yellow Warblers in California have declined in recent decades. Although overall population size of Yellow Warblers have not been estimated, there is much cause for concern given the decline and extirpation in many areas throughout California and the Western States.

This fragmentation of habitat may be adversely affecting migratory birds during their migration as well as on the breeding grounds. Many bird species, the Neotropical migrants, annually make long distance movements from breeding grounds in the North American temperate zones to wintering grounds south of the continental United States. These long-distance migrant passerines do not, or cannot, carry enough fat reserves to allow them to migrate the full distance between their breeding and wintering areas. Therefore, the availability of suitable en rout habitats where passage migrants can safely and rapidly deposit energy reserves is critical to a successful migration. Since migratory birds must pass through a series of environments in their annual migrations, some authors believe that they are particularly vulnerable to habitat alterations. As fragmentation continues to occur, these islands of riparian habitat will become more and more critical to the survival of migrants. In fact, removal of riparian woodland in the Central Valley of California may now be limiting nesting populations to the north.

For more details on my studies, check out these links!

Sexual Differences in Wilson's Warbler Migration (look at the seventh article in the list)