Bird and butterfly community structure and songbird next success in montane meadows of the Greater Yellowstone Ecosystem

Abstract

<p>We performed bird and butterfly surveys from 1996 to 2004, and Yellow Warbler nest surveys in 2002 and 2004. Bird and butterfly surveys took place in two regions of the Greater Yellowstone Ecosystem. The northern region, or "Gallatins", consisted of the northwest corner of Yellowstone National Park and the western edge of Gallatin National Forest. The southern region, or "Tetons", included Grand Teton National Park extending slightly into Bridger-Teton National Forest. The bird and butterfly surveys (25 sampling sites in each region) were used to relate species composition to montane meadow types, which we classified along a hydrological gradient using remotely-sensed satellite imagery. We also related shifts in species composition to temporal changes in the Normalized Difference Vegetation Index (NDVI), which we used as a surrogate measure of climate (e.g., temperature and precipitation). NDVI measures were derived from the same satellite imagery used to construct the habitat classification. We found that Gallatin butterflies in mesic (as opposed to dry or wet) meadows exhibited concurrent shifts in species composition correlated with NDVI between the years 1997 and 2000, and between the years 1998 and 2000. Yellow Warbler nest surveys were performed only in the Tetons and were restricted to willow habitats. We hypothesized that waterway density within each nest territory would indirectly lower nest success by attracting high densities of garter snakes, which would then opportunistically prey on warbler nests. We used a recently published method of nest success analysis known as logistic-exposure, which is a logistic regression technique slightly modified via its logit link function. We found a significant negative effect of waterway density on nest success in our Pacific Creek study site, with a parameter estimate of -0.048 and a 95% confidence interval of [-0.086, -0.012]. We concluded that butterflies in the Gallatins responded at the community level to changes in vegetation within certain habitat types, which in turn reflected general climate patterns over specific time periods. We also concluded that waterway density can be used as an indirect predictor of nest success in Yellow Warblers, provided other predators are taken into account.</p>