Avian responses to Conservation Reserve Enhancement Program grasslands in Pennsylvania

During years 2000-2005 40,000 ha of former agricultural fields in southern Pennsylvania were sown with grasses and legumes through the Conservation Reserve Enhancement Program (CREP).  The primary aims of the CREP are to reduce soil erosion and improve water quality, but it is also anticipated that the new grassland habitat will enhance farmland bird populations, which have declined greatly in the region in recent decades.  We carried out a local-scale study of bird community use of 103 CREP fields in 2002-2004, and a landscape-scale bird population monitoring study on 89 bird survey routes in 2001-2005.  Our local-scale study revealed that small numbers of grassland birds occupied the CREP fields; along with larger numbers of bird species usually associated with shrub and field edge habitats.  At the landscape-scale, we detected significant positive population responses for several bird species, especially in areas where there was a higher rate of enrollment of land into the program (>4% of farmland).  A Bayesian spatial model showed that population responses by grassland birds may have be limited by a lack of source populations in an area where these species are scarce and localized.  We conclude that CREP has provided an important new habitat for a wide range of bird species in southern Pennsylvania, but that population level responses by grassland obligate bird species will be modest in the short-term.