The effectiveness of the conservation reserve program's native seeding requirement in providing breeding and wintering habitat for grassland birds in the southern hign plains of Texas
Thompson, Thomas R.
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To increase the value of Conservation Reserve Program (CRP) fields as wildlife habitat, the Farm Bill of 1996 required participants with existing CRP contracts in Texas to re-seed 51% of existing CRP fields with native grasses. Additionally, all new CRP contracts require 90% of the land enrolled to be m native grass species mixes. However, the direct value of native seeding for grassland birds has not been evaluated fully m the Southern High Plains of Texas. We examined bird use and productivity during the breeding season, and bird use during the whiter among 4 principle CRP cover types: (1) Old World bluestem (OWB) (Bothriochlora ischaemum), (2) weeping lovegrass (WLG) (Eragrostis curvula), (3) native grass mix (NAB) including buffalo grass (Buchloe dactyloides), and (4) native grass mix without buffalo grass (NAA). For 2001 and 2002 breeding season, 12 avian species were observed in the study fields. Species number, richness, and total abundances of birds did not differ between cover types or between years for overall avian abundances during the breeding season and May surveys. Grasshopper Sparrow (Ammodramus savannarum), Cassin's Sparrow (Aimophila cassinii). Mourning Dove (Zenaida macroura), and Western Meadowlark (Strunella neglecta) accounted for more than 95% of all observations for the two years. Grasshopper Sparrows were the most abundant species m all cover types except NAA, being hi roughly equal proportion to Cassin's Sparrows m these fields. Grasshopper Sparrow abundances were higher m NAB and OWB fields during both the overall breeding season and May survey periods. Grasshopper Sparrows were associated with fields that had low percent bare ground, high percent grass cover, low to moderate vertical densities, and low overall vegetation heights. Cassin's Sparrow abundances were higher hi NAA fields compared to NAB and OWB fields for both the overall breeding season and May surveys. Cassin's Sparrows were associated with fields with moderate shrub densities (> 2 per 50 m ) and/ or moderate to high percent bare ground (> 30%). Western Meadowlarks occurred m low abundances across all CRP cover types and did not show any consistent relationship based on vegetation characteristics within cover types. Mourning Doves occurred in low abundances across all cover types, but were more abundant in introduced grass fields compared to native grass mix fields. Nests of 7 species were found m CRP fields. Grasshopper Sparrow (29.7%), Cassin's Sparrow (23.7%), and Mourning Dove (38.1%) accounted for 91.5% of all nests located. Grasshopper Sparrow nest densities were higher hi NAB fields compared to NAA fields. Cassin's Sparrows were not found to nest hi NAB fields and were equally abundant among the other cover types. Overall more Cassin's Sparrow nests were found hi NAA and range fields compared to other cover types. Mourning Dove preferred introduced grass fields compared to native grass mixes, being higher m WLG and OWB fields. Nest success estimates for all species were similar among cover types and between CP types for the years combined. Winter avian abundance, species richness, and number of species differed among CRP cover types. Native grass mix CRPs supported more avian species and higher abundances of species during the whiter than introduced grass CRPs. Western Meadowlark (36.9%), Savannah Sparrow (24.7%), and Homed Lark (32.5%) were the most common species observed for the two years, accounting for 94.1% of all species. Western Meadowlarks were common across all cover types, while Savannah Sparrows and Homed Larks were more abundant on the native grass mix CRPs. The native seeding requirement of CRP has likely contributed to abundances of avian species within the Southern High Plains of Texas during the breeding and wintering season. The more diverse native grass mixes in term of both species composition and structure influences the use of these cover types by several different species throughout the year. Results of this study provide a clearer understanding of the applicability of CRP plantings as a conservation tool for grassland passerines.