Long-term Changes in Breeding Bird Populations and Habitat, Laidlaw Park, Craters of the Moon National Monument, ID

Rich, Terry

This report documents a revisit to 10 line transects that were established in 1980 for the purpose of assessing the occurrence and density of breeding firds. Transects were located to examine the differences in communities dominated by big sagebrush (Artemisia tridentada tridentada), three-tip sagebrush (A. tripartida), and cheatgrass (Bromus tectorum). Changes in populations are analyzed and discussed. In 1980, I established line transects in the Monument Resource Area of the Bureau of Land Management’s Shoshone District to assess the occurrence and density of breeding birds in three different vegetation types - big sagebrush, three-tip sagebrush, and cheatgrass. In 2002, 2003, and 2004 I resampled the birds and vegetation on seven of the original transects. The main objective of this study was to assess population trends in breeding birds of the area. Measurements of vegetation showed that little had changed between the early 1980s and early 2000s. In fact, there were no significant changes in the vegetation variables measured over all sites combined. It is most noteworthy that cheatgrass had not expanded its coverage in general in the area, despite its increase across the Columbia Plateau and Intermountain West in general. A total of 1084 detections of 23 bird species were made over all years and transects. The most common species were Brewer's Sparrow, Western Meadowlark, Horned Lark, Vesper Sparrow, and Sage Thrasher. There was no trend in detections over time for the 15 most common species combined or for the five most common species combined. However, Brewer’s Sparrow declined significantly over the study period, particularly on three-tip sagebrush sites. Sage Thrashers also declined significantly while Western Meadowlarks and Horned Larks increased significantly. There was no significant trend for Vesper Sparrows, Brown-headed Cowbirds, or Common Ravens. Thus, there were significant increases in two widespread, generalist grassland species – Western Meadowlark and Horned Lark – and significant declines of two sagebrush obligates – Brewer’s Sparrow and Sage Thrasher. We do not know if their decline is due to factors on the study area during the breeding season or to those occurring elsewhere. A productivity study of Brewer’s Sparrow and Sage Thrasher in the study area would be valuable in helping to determine whether the limiting factor is operating during the breeding or non-breeding periods. On the other hand, trends for all five of the most common species are better than those on the Carey Breeding Bird Survey route, the state of Idaho, or the Columbia Plateau. This may be the result of two factors. First, the study area is part of a large region of sagebrush that is relatively unfragmented and undisturbed by human activity. Second, the three-tip sagebrush ecosystem may be particularly resilient. We know that this species sprouts following fire so that it recovers relatively quickly. But it also appears to be resistant to invasion by cheatgrass. If so, Laidlaw Park and similar three-tip regions may be extremely important to the future of sagebrush conservation. Although this sagebrush does not support Sage Sparrows, at least in this area, it does support the other sagebrush obligate birds. I recommend an assessment of the extent of the three-tip sagebrush ecosystem in the western U.S. and the degree to which other high priority sagebrush species find this sagebrush to be source habitat. In conclusion, the Laidlaw Park area may be much more valuable to the long-term persistence of the sagebrush avifauna than most people realize.