Restoring Bird Habitat Details

What Species: Overwintering Neotropical migrants, including Bewick's Wren (Thryomanes bewickii), Orange-crowned Warbler (Vermivora celata), Yellow-rumped Warbler (Dendroica coronata), Common Yellowthroat (Geothlypis trichas), Spotted Towhee (Papilo maculatus), Lincoln's Sparrow (Melospiza lincolnii),White-crowned Sparrow (Zonotrichia leucophrys).

Where: Yucatan Peninsula, Quintana Roo; Ayuquila River, Jalisco; Colorado River Delta, Sonora; Baja California; Sacramento Valley, California; San Joaquin Valley, California.

Who: Dr. Steven Latta (National Aviary) and locally-based partners at each site.

When: 2004 – present

Why: Populations of many once common species of songbirds are declining. At the same time, the official listing of species as threatened or endangered is becoming politically problematic and financially difficult. Thus, new habitat conservation efforts must increasingly focus on the needs of multiple species that are still common enough to be able to respond to acquisition, restoration, and land management changes.

Currently in California and elsewhere, billions of dollars are being invested in habitat enhancement activities with little knowledge of the biological needs of affected species and no evaluation of their efficacy. It is imperative that managers answer the question, “Do our projects work to improve wildlife values for multiple species?” If projects do not engage broad interests and lack scientific basis, well-intentioned conservationists may not only waste money but may also contribute to ecosystem decline.

Riparian habitat is one of the most important types of habitat for birds. In California, riparian areas have been identified as the single most important habitat for the protection and conservation of songbirds and support a disproportionately high number of migrants. However, it is estimated that at least 98 percent of riparian habitat in the Central Valley has been lost in the past century through human-induced changes, including urban development, water diversions, and conversion to agriculture.

In response to these changes, public and private organizations are investing millions of dollars in riparian conservation including restoration, enhancement, and acquisition, with thousands of acres slated for restoration along major California and western rivers and their tributaries. Measuring multiple bird species response to these conservation efforts will help guide management and provide a cost-effective evaluation of restoration activities.

Project Description and Current Status: A key element of any successful riparian restoration program is evaluation, monitoring, and adaptive management to ensure restoration goals that include positive benefits to wildlife are met. Monitoring multiple species of birds is a relatively easy and cost effective way to track changes in natural systems. While we have been successful in assessing the importance of riparian habitats and have fundamentally changed the way restoration is implemented for breeding songbirds, similar data for nonbreeding communities are severely lacking.

Because many species of wintering migrants have been shown to segregate by sex and age class, abundance data alone can be a misleading indicator of population size and habitat preference. Furthermore, abundance cannot be equated with survival, so data on site fidelity, including overwinter site persistence and annual return rate, are required to assess habitat quality. Thus, recent studies have focused on habitat-specific demographies and site fidelity of wintering warblers.

Our protocol is based on previous work on migrant winter ecology and habitat preferences. Unlike protocols which depend on capture-recapture models alone to determine site fidelity and survival, this intensive protocol allows analysis of data from a small number of related sites because of the inclusion of resight data and the ability to then track more individuals in the color-banded population.

Wintering Neotropical migrants are now being investigated at plots in 6 watersheds (2 Californian, 4 Mexican). In each watershed we have 2-4 sites of 12-20 ha each in well-conserved riparian habitat or restored riparian habitat. At 2 Mexican watersheds (Baja California and Yucatán Peninsula) we did not locate plots in restored habitats because restoration activities have not yet been undertaken.

Three rounds of point counts and constant-effort mistnetting are taking place in early-winter (November), midwinter (early-January), and late-winter (late-February to early-March). Following banding efforts, each site is being systematically searched for color-banded individuals, and their location and any territorial behavior is recorded on a map of the plot. Resighting continues until observers are confident that no colorbanded birds remain unidentified on or near the site. Resighting of color-marked birds will be used to determine site fidelity and overwinter site persistence or survival over the winter nonbreeding season.

Intensive monitoring will also provide badly needed data on life history traits and demography of species, and provide direct information on habitat conditions necessary for overwinter survival. Together these data are required to assess the winter ecology of Neotropical migratory birds and habitat conditions for land and species management.

University students from Mexico have been recruited to take lead roles in research activities at three of the Mexican field sites, and this work will be included in their theses. Other students or aspiring biologists have been integrated as interns for field work and serve at each site as trainees to master field research and avian monitoring techniques. Each intern is being mentored by a trained biologist.

Current Goals: We are relating bird use, overwinter site persistence, and survivorship to restoration design, silvicultural practices, water flow regimes, and other restoration activities. Because in this study we are able to work simultaneously in well-conserved riparian plots and restoration plots, and because these sites have been previously assessed as breeding habitat for Neotropical migrants by PRBO and partners, we are in a unique position to: (1) describe the wintering ecology of Neotropical migrants in riparian habitat in both the temperate and tropical zones; (2) evaluate the value of riparian restoration efforts for migrants during the nonbreeding period; and (3) test whether restoration conditions favorable to breeding birds translates to conditions favorable to wintering birds.

Next Steps: Field work for this four-year study has been completed.

Funding: This project has been supported by the U.S. Fish and Wildlife Service through the Neotropical Migratory Bird Conservation Act, the Sonoran Joint Venture, and by PRBO Conservation Science and their partners and donors.

Related Scientific Publications:

Latta, S. C. 2012. Use of data on avian demographics and site persistence during overwintering to assess quality of restored riparian habitat. Conservation Biology 26:482-492.

Latta, S. C., H. de la Cueva, and A. B. Harper. 2012. Abundance and site fidelity of migratory birds wintering in riparian habitat of Baja California. Western Birds 43:90-101.

Latta, S. C., C. J. Ralph, and G. R. Geupel. 2005. Strategies for the conservation monitoring of resident landbirds and wintering Neotropical migrants in the Americas. Ornitologia Neotropical 16:163-174.