Initial response of bird populations to conservation grasslands in southern Pennsylvania

Abstract

Since 2000, around 40,000 ha (99,000 ac) of conservation grasslands have been established in southern Pennsylvania through the Conservation Reserve Enhancement Program (CREP). We tested whether CREP enrollment in 2000 to 2004 provided sufficient new habitat to elicit landscape-scale population responses among nine songbird species previously shown to nest in CREP fields. We used hierarchical spatial models to examine bird population trends in 90 landscapes (mean size 1,400 ha [3,460 ac]) with respect to rates of CREP enrollment. By 2004, an estimated 2.4% of farmland in our study region was enrolled in CREP with amounts within landscapes ranging from 0% to 17%. However, CREP fields were often small (mean = 3.9 ha [9.6 ac]), which may reduce their suitability for area-sensitive grassland obligates. Nonetheless, our predictive models suggest that by 2005, numbers of three species were significantly higher than they would have been if there was no CREP enrollment: field sparrow (Spizella pusilla; 19.4% higher), song sparrow (Melospiza melodia; 8.0% higher), and eastern meadowlark (Sturnella magna; 31.6% higher). There were nonsignificant negative associations between CREP enrollment and trends of grasshopper sparrow (Ammodramus savannarum) and vesper sparrow (Pooecetes gramineus). Our study was conducted during the establishment phase of the program, and repeat surveys will be necessary to fully evaluate long-term responses. Detection of population-scale responses soon after program establishment was encouraging, but the program does not appear to be benefitting all grassland songbirds.