Factors affecting habitat use and abundance patterns of birds in a grassland-savanna-woodland habitat mosaic.

摘要

Since European settlement, land-use practices have altered the structure and composition of grassland, savanna, and woodland habitats in southwest Wisconsin. Many species of birds use these habitats, including species of conservation concern. However, it is unclear how historic and current changes in land cover affect avian biodiversity patterns. Using remotely sensed, ground-collected, and historic Public Land Survey System data, and univariate and multivariate statistical methods, I explored the utility of image texture for characterizing avian habitat, tested the relationship between avian abundance and remotely sensed metrics, examined how habitat management for an endangered butterfly affects the avian community, and shed light on how shifting tree composition may affect habitat quality for neotropical migrants during spring migration stop-over. Remotely sensed image texture can be used to characterize avian habitat, as described by the vegetation structure indices foliage-height diversity and horizontal vegetation structure, in a grassland-savanna-woodland mosaic. Additionally, image texture does predict density of Grasshopper Sparrow (Ammodramus savannarum) within grassland and Ovenbird ( Seiurus aurocapillus) within woodland, as well as avian species richness among habitats. Oak savanna habitat management for the Federally endangered Karner blue butterfly (Lycaeides melissa samuelis) positively influenced avian community composition and benefited several avian species of conservation concern. I found that an important management consideration for maximizing benefits to both Karner blue butterflies and savanna birds is landscape placement of the management activities. Songbird species that use tree foraging substrates during spring migration stop-over at Kickapoo Valley Reserve woodlands use red oak (Quercus rubra), white oak (Q. alba), American elm (Ulmus americana) and slippery elm (U. rubra) more frequently than they would if using these species in proportion to their availability. The proportional use of shade-tolerant tree species such as sugar maple (Acer saccharum ), red maple (A. rubrum) and basswood ( Tilia americana) was much lower than would be the case if these species were used in proportion to their availability. Forest composition has changed markedly between the 1850s and 2010, but is still dominated by maple and oak. The sapling composition was overwhelmingly sugar maple.