Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Wildlife and Fisheries Resources
Petra Bohall Wood.
Analysis of North American Breeding Bird Survey (BBS) data has identified the Cerulean Warbler (Dendroica cerulea) as a species of conservation concern with an annual population decline of 4.1% from 1966--2007. BBS data has shown persistent declines for Cerulean Warblers in their core breeding range of the Central Appalachians. No previous studies have examined the relationship between habitat change and Cerulean Warbler abundance at BBS stops, and/or whether BBS declines reflect changes occurring only at sampled routes or reflect regional Cerulean Warbler population declines. The objectives were to (1) quantify the effects of land cover and forest fragmentation metrics on Cerulean Warbler populations over several time periods along BBS stops, and (2) compare stop-level habitat and Cerulean Warbler detections between the BBS roadside surveys and an off-road dataset to determine if off-road habitat and population trends are being accurately assessed by roadside surveys.;We examined the effects of land cover and fragmentation change on Cerulean Warbler populations within a 300 m buffer of stops along BBS routes using aerial photos and the National Land Cover Dataset (NLCD). Aerial photos were available for 68 stops along two routes from 1967/1971 (early period) to 1982 (middle period), and from 1982/1985 (middle period) to 2000/2003 (late period) for 240 stops along six routes. Data were collected from 1,377 stops along 28 BBS routes using the 1992 and 2001 NLCD.;In aerial photo interpretation, composite land cover was replaced by deciduous/mixed forest between the early and middle time period, however deciduous/mixed forest did not change from the middle to late time period. Cerulean Warbler detections decreased between the early and middle and middle and late time periods. The lack of a change in most fragmentation variables believed to be important to Cerulean Warblers, such as interior, unfragmented deciduous forest suggests that there may be other microhabitat variables influencing the population trends of Cerulean Warblers.;From 1992 to 2001 using the NLCD, the amount of deciduous/mixed forest, amount of core forest area, and forest-forest edge density decreased. However, Cerulean Warbler detections did not change between these two time periods along the same BBS stops. When we restricted analysis to stops that had a Cerulean Warbler detected in either 1992 or 2001, we found similar responses from habitat variables over time, but Cerulean Warbler detections increased over time. The response from Cerulean Warblers along these stops may be because of the influence of microhabitat features, such as canopy gaps that we were unable to measure due to the coarse nature of the NLCD. In addition, Cerulean Warblers may be able to tolerate some degree of edge habitat, as Cerulean Warblers increased in the presence-only analysis as forest-nonforest edge density increased.;We compared land cover, fragmentation and physiographic metrics, and Cerulean Warbler abundance for 1,525 stops along 31 BBS routes and 1,375 off-road stops using the 2001 National Land Cover Dataset. All the land cover and six of the eight habitat variables differed between BBS and off-road datasets. Although the off-road dataset had greater amounts of habitat characteristics Cerulean Warblers seem to prefer, the BBS detected more birds per stop than the off-road dataset. BBS stops had greater densities of forest-forest and forest-nonforest edge habitat, suggesting Cerulean Warblers tolerate or select for a degree of edge in determining habitat suitability. Although three of the four land cover variables were different in presence-only analysis, nearly all of the habitat metrics and Cerulean Warbler detections were not different between the BBS and off-road datasets. From these results, we suggest that although habitat along BBS stops is different than off-road areas, Cerulean Warblers are able to find suitable habitat near roads. Since Cerulean Warblers were detected more frequently and at higher abundance along BBS stops, the estimated 4.1% annual decline from BBS data may be affecting a larger proportion of the population.
McElhone, Patrick Michael, "Cerulean Warbler population and habitat changes along Breeding Bird Survey routes in the Central Appalachians" (2009). Graduate Theses, Dissertations, and Problem Reports. 2776.