SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.2.2.4. Willow Flycatcher (Extimus trailii adastus and brewsterii)

This section updates and supplements the information found in FEIS, Volume 3, Chapter 3, Part 4.4, pp. 143-161.

Although the willow flycatcher population in the Sierra Nevada is known to have dramatically declined after 1940, the current direction and magnitude of the demographic trend are uncertain (Serena 1982, Stafford and Valentine 1985, Flett and Sanders 1987, Harris et al. 1987, 1988, Valentine et al. 1988, Sanders and Flett 1989, H. Bombay pers. comm.). However, if available and preliminary nesting site re-occupancy data as well as central Sierra Nevada nest success and fecundity rates are used as a metric for population trend, it appears that the willow flycatcher population in the Sierra has continued to seriously decline during the past two decades (Morrison et al. 2000).

Recent Surveys

Although there are many uncertainties regarding willow flycatcher distribution, abundance, and demographic data in the Sierra Nevada bioregion, monitoring of willow flycatcher populations and habitat conditions on National Forests in the planning area has increased significantly since the Sierra Nevada Framework Project ROD was approved in 2001. As a result of the survey requirements directed under the ROD, Forests have worked diligently to complete the necessary surveys. The Forest Service conducted willow flycatcher survey training workshops in 2001 and 2002 for biologists and technicians charged with conducting these surveys. Over 50 employees were trained during these 2 days workshops to conduct willow flycatcher surveys to protocol. The survey workshop will be held annually to train new employees and refresh the skills of previously trained employees conducting the surveys.

Surveys conducted in 2001 and 2002 resulted in all of the 82 (now 81) originally specified known willow flycatcher sites (under the SNFP ROD) being surveyed to protocol. In addition to surveying the 82 known sites, many Forests have completed the surveys for the most of the emphasis habitats as identified by the ROD. As of January 2003, 5 of the 11 National Forests in the SNFPA planning area reported that all of the willow flycatcher emphasis habitat meadows had been identified and mapped, while the other 5 Forests reported that this process was well under way (Stefani 2003). Surveys to protocol of these areas have been completed for 133 meadows of the 496 potential emphasis habitat meadows identified under the ROD. Results of these surveys have documented 11 new willow flycatcher territories. The remaining areas are currently being evaluated to determine if suitable habitat exists in order to warrant protocol surveys (Stefani 2003).

Recent data available from the demographic and monitoring study in the north central Sierra is not encouraging with regards to willow flycatcher population trends. The total number of territories at 15 monitoring sites in the north central Sierra declined from 62 in 1998 to 45 in 2001. Data from 2002 shows an even more alarming trend with the number of territories documented at these same 15 sites down to 37 territories (Bombay and Morrison 2003). Perrazo Meadows on the Tahoe National Forest has been consistently surveyed since 1997. The number of territories at Perazzo Meadows has declined from a high of 12 in 1997 to a current low of only 2 in 2002 (Bombay and Morrison 2003).

Consistent survey efforts on the Sierra and Stanislaus National Forests in the past several years show a lack of willow flycatcher occurrence at a number of well-documented breeding areas in the central and southern Sierra Nevada. In addition, three years of surveys on the Sequoia National Forest have failed to re-confirm occupancy of willow flycatchers.

Brood parasitism

The impact of brown-headed cowbirds varies within the Sierra Nevada bioregion. Long term research shows that brown-headed cowbirds impact willow flycatcher populations outside the planning area (Sedgwick and Iko 1999, Whitfield 1990, Whitfield and Enos 1996, Whitfield and Sogge 1999). Although brown-headed cowbirds have impacted less than 7 percent of observed willow flycatcher nests in the Sierra Nevada between 1997-2000, their influence could become greater if willow flycatcher populations decrease, brown-headed cowbird populations increase, or both occur (Whitfield and Sogge 1999, Smith 1999, Morrison et al. 2000, H. Bombay pers. comm.). Given that mountain communities are expanding in many areas, and brown-headed cowbirds are highly associated with human disturbance, brown-headed cowbirds are likely to increase in at least some portions of the bioregion (Verner and Ritter 1983).

In the Lake Tahoe Basin in 1998 through 2000, high cowbird abundance translated into 8 of 18 nests (44 percent) being parasitized (Morrison et al. 2000). Smith (1999 in Stefani et al. 2001) in a review of recent cowbird studies suggests that management actions to control cowbirds may not be warranted unless the parasitism rate is at least 60 percent, however he lists criteria that might suggest using a lower rate, including: restricted habitat, isolated population, and population in prolonged decline. This indicates that the few remaining breeding locations within the Tahoe Basin may benefit from cowbird management if the current parasitism rate remains consistent or increases (Whitfield and Sogge 1999, Whitfield et al. 1999). Nonetheless, high brown-headed cowbird density and high private land ownership in the area could make control difficult and limit its effectiveness (Citta and Mills 1999 in Stefani et al. 2001, Hall and Rothstein 1999, Smith 1999, Whitfield and Sogge 1999, H. Bombay pers. comm.). Brown-headed cowbird trapping programs and livestock facilities removal or relocations will need to be evaluated based on risk levels and effectiveness, prior to implementation (Verner and Rothstein 1988, Smith 1999, Whitfield and Sogge 1999, Whitfield et al. 1999).

In 13 documented cases of brown-headed cowbird brood parasitism of willow flycatcher nests for which dates are known in the central Sierra Nevada, parasitism events occurred from approximately June 17 to August 4 (mean = July 4, SD = 12 days) (Sanders and Flett 1989, H. Bombay pers comm.). These parasitism dates correspond to willow flycatcher incubation initiation dates between June 15 and August 1 (Stafford and Valentine 1985, Sanders and Flett 1989, H. Bombay pers comm.). Regional information on cowbird egg laying dates and willow flycatcher incubation initiation dates will need to be compiled as some regions and elevations of the Sierra Nevada may have different dates. In the Dinkey Creek area of Sierra National Forest, Verner and Ritter (1983) found that cowbirds seldom frequented pack stations prior to the arrival of pack animals. Thus, delaying access to livestock and pack stock facilities in relation to estimated dates of brood parasitism might eliminate or alleviate this threat in some areas of the Sierra Nevada.

Bombay and Morrison (2003) reported an increase in cowbird parasitism in 2000 (6 events) and 2001 (5 events). The reason for this increase is not completely known, however, it is suspected that it could be partially due to the slightly earlier nesting onset for willow flycatchers documented during those two years. This would have resulted in a greater overlap in timing of breeding with brown-headed cowbirds (Verner and Rothstein, 1988.)

USDA Forest Service · Pacific Southwest Region