Academic journal article The American Midland Naturalist

A Comparison of Conservation Reserve Program Habitat Plantings with Respect to Arthropod Prey for Grassland Birds

Academic journal article The American Midland Naturalist

A Comparison of Conservation Reserve Program Habitat Plantings with Respect to Arthropod Prey for Grassland Birds

Article excerpt

ABSTRACT.-The Conservation Reserve Program (CRP) was designed to reduce soil erosion and curb agricultural overproduction by converting highly erodible agricultural land to various forms of perennial habitat. It has had an incidental benefit of providing habitat for wildlife and has been beneficial in reversing population declines of several grassland bird species. However, the mechanisms behind these reversals remain unknown. One such mechanism may be differences in food availability on CRP vs. non-CRP land or between different types of CRP. The influence of CRP habitat type on the abundance of arthropod prey used by grassland birds has not been previously explored. We compared the abundance and diversity of arthropods among four CRP habitat types in Texas [replicated plots of exotic lovegrass (Eragrosiis curvula), Old World bluestem (Bothriochloa ischaemum), mixed native grasses with buffalograss (Buchloe dactyloides) and mixed native grasses without buffalograss] and native shortgrass prairie. Attention was focused on adult and juvenile spiders (Order Arancae), beetles (Coleoptera), orthopterans (Orthroptera: grasshoppers and crickets) and lepidopterans (Lepidoptera: butterflies and moths), as these taxa are the primary prey items of grassland birds during the breeding season. Arthropod diversity and abundance were higher on indigenous prairie compared to CRP, reflecting differences in vegetative diversity and structure, but there were no differences in arthropod richness or abundance among CRP types. These results indicate that, although CRP is not equivalent to native prairie in terms of vegetation or arthropod diversity, CRP lands do support arthropod prey for grassland birds. More direct assays of the survivorship and fitness of birds on CRP compared to native shortgrass prairie are clearly warranted.

INTRODUCTION

The Food Security Act of 1985 authorized the United States Department of Agriculture (USDA) to institute the Conservation Reserve Program (CRP) to combat soil erosion and agricultural overproduction (USDA, 2000). This voluntary program is administered by the Farm Service Agency and uses financial incentives to retire private land from agricultural production. Land is leased for 10-15-y contracts, during which time it is seeded in perennial grasses and/or legumes and not plowed (Young and Osborn, 1990; Ohlenbusch et al., 1995). Grazing and haying are allowed but only temporarily for emergency provisioning of livestock. The legislation authorizing the CRP has been modified several times since 1985, and now the program focuses primarily on replacing marginal agricultural land with native habitats and protecting wetlands. Nearly 14 million ha currently are enrolled in the U.S. (USDA, 2000). As an incidental benefit, this program has provided valuable habitat for wildlife, such as grassland birds (Berthelsen and Smith, 1995).

Grassland birds have exhibited the most consistent, widespread and rapid declines of any group of North American birds (Askins, 1993; Knopf, 1994, 1996; Herkert, 1995; Peterjohn and Sauer, 1999; Vickery et al., 1999). One-third of North American endemic grassland bird species have experienced statistically significant declines in abundance in the past 30 y (Knopf, 1996). These declines can be attributed in part to the loss of over 99% of indigenous grassland in most areas of the Great Plains (Noss et al., 1995). Texas, for example, has lost approximately 90% of its original native shortgrass prairie (6,480,000 ha; Samson and Knopf, 1994), but has over 900,000 ha enrolled in the GRP (Berthelsen et al., 1989).

The availability of CRP has been linked to reversing population declines in some species, especially for field sparrow (Spizella pusilla), grasshopper sparrow (Ammodramus savannarum), LeConte's sparrow (Ammodramus leconteii), lark bunting (Calamospiza melanocorys), chestnut-collared longspur (Calcarius ornatus) and western meadowlark (Sturnella neglecta) (Johnson and Schwartz, 1993; Reynolds et al. …

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