oikonos

Status and Breeding Biology of an Isolated Population of Bendire's Thrashers in California: a Study Proposal

Lee Flat in Death Valley National Park, which harbors the only known Bendire's Thrasher breeding population in the northern Mojave. At 5780' it is also the highest known breeding elevation for this species. Dominant shrubs of the Lee Flat area where Bendire's were historically observed consisted primarily of Hopsage, Spiny Menodora, Blackbrush, Atriplex, and others. (Photo by authors)

Summary of preliminary surveys for Bendire's Thrasher (Toxostoma bendirei) in Lee Flat, Death Valley National Park, California.

We visited Lee Flat on three occasions (April 18-19, May 10 and May 24) during the spring of 2003 searching for presence of Bendire's Thrashers. No Bendire's Thrashers were located, although three species of mimids were detected.

Searches for thrashers were conducted both on foot and on road transects. Foot surveys were conducted in the morning by walking transects approximately a mile long through the area and habitat where previous sightings were concentrated. We listened and watched for thrashers, and in some instances played taped recordings of Bendire's thrasher songs to elicit a response. Road surveys were conducted in late mornings and early evenings by broadcasting Bendire's thrasher songs every .25 to .4 miles. Road transects consisted of 4 to 11 points.

Overview of activities by date:

April 18 - we walked transects through the appropriate habitat in the morning, and conducted two road surveys (4 and 5 points, respectively) in the late morning and evening. Several Sage thrashers were observed in the area where Bendire's thrashers had been observed in the early and mid 1990's. A few male Sage thrashers were singing, and a Sage thrasher carrying nesting material was observed.
April 19 - we walked more transects in morning, and spent the rest of the day exploring the surrounding areas and habitats, primarily the nearby Santa Rosa valley and the slopes above Lee Flat. We found that the habitat, particularly the shrub understory, of Lee Flat was unmatched by the surrounding areas we explored.

May 10 - We walked similar transects in the morning, this time broadcasting Bendire's Thrasher songs approximately every 200-300m. No Bendire's were observed, however Sage thrashers, apparently the same pairs that were observed previously with nesting material, were observed with food carries. During the road survey, a LeConte's Thrasher approached us, and seemed to follow us for several hundred meters. It did not seem tied to a particular territorial location. Northern mockingbirds were also observed and found to be fairly common throughout the areas we visited.

May 24 - Similar foot and road surveys were conducted. A pair of LeConte's Thrashers was observed near where the lone bird had been on the 10th. The male sang vociferously, the female briefly sang, and they were observed visiting a nest, apparently under construction. More Sage thrashers were observed, including another food carry in an area different from where Sage thrashers were previously observed.

In summary, no Bendire's Thrashers were detected, and based on our surveys during the three visits we feel confident none were present in 2003. The shrub density and diversity of Lee Flat seemed restricted to the area we surveyed. Shrub cover at the nearby Santa Rosa valley was relatively sparse, and the slopes above Lee Flat differed in shrub understory, primarily by sagebrush (Artemisia) becoming more dominant with increased elevation. Dominant shrubs of the Lee Flat area where Bendire's were historically observed consisted primarily of Hopsage, Spiny Menodora, Blackbrush, Atriplex, and others.
The fairly widespread presence of Northern mockingbirds in Lee Flat was interesting. Northern mockingbirds are primarily year-round residents and could be at an advantage in establishing and maintaining territories before the return of the migrant Bendire's thrasher, and possibly out-competing them Northern mockingbirds are successful in living around human habitations, and are apparently increasing in Bendire's thrasher habitat and range. Thrasher surveys conducted in the western and northern Mojave desert in 2001 which replicated England and Laudenslayers' previous thrasher surveys of 1986-87 found Northern mockingbirds nearly twice as abundant in 2001 as they had been in 1986-87 (266 NOMO in 2001 verses 159 in 1986-87), and Bendire's Thrashers were scarcely found in the recent surveys (3 BETH found in 2001 verses 31 in 1986-87) (Jones and Stokes unpublished report, 2002).
We plan to continue similar survey efforts in the spring of 2004 (see our proposal for details). The Bendire's thrasher population at Lee Flat may breed sporadically. Future survey efforts will help determine the status of the Bendire's thrasher at the northern edge of its range.

Jones and Stokes Associates, 2002.Mimid surveys in the Western Mojave Desert with special focus on the Bendire's Thrasher. Unpublished report.