Multi‐region response to conservation buffers targeted for northern bobwhite

Abstract

We coordinated a large‐scale evaluation of northern bobwhite (Colinus virginianus) population response to establishment of 9‐m to 37‐m linear patches (buffers) of native herbaceous vegetation along row‐crop field margins as part of the Conservation Reserve Program practice Habitat Buffers for Upland Birds (CP33). We compared northern bobwhite covey densities on 1,088 paired row‐crop fields with and without native herbaceous buffers in 13 states during autumn, 2006–2008. We used a 2‐stage random effects modeling approach that incorporates the effective area as an offset in generalized linear mixed models to assess regional relationships among autumn bobwhite covey densities and covariates of field type (i.e., fields with vs. without native herbaceous buffers), ecological region, year, survey week, and contracted vegetative cover (i.e., planting native grasses and forbs vs. establishing through natural regeneration). Covey density was correlated with year and interaction effects of field type and ecological region. The year effect suggested annual variation in covey densities, whereas the field type by ecological region interaction suggested covey response to buffers was dependent on spatial location, likely reflecting differences in buffer establishment, succession, and characteristics of the surrounding landscape among regions. Mean fitted covey density on fields across all survey sites was 0.047 (±0.008 bootstrap standard error [BSE]) and 0.031 coveys/ha (±0.003 BSE) on row‐crop fields with and without herbaceous buffers, respectively. Covey density was greater on fields with buffers relative to matched, comparison fields without buffers in the Mississippi Alluvial Valley (241%; P < 0.001) and both the eastern (123%; P < 0.001) and western (60%; P = 0.01) portions of the Southeastern Coastal Plain region. Covey density was an order of magnitude greater in the central Texas region compared to other regions, but exhibited a small response to native herbaceous buffers, as did density of coveys in the Eastern Tallgrass Prairie and Central Hardwoods regions. Disproportionate response to buffers in the Mississippi Alluvial Valley and Southeastern Coastal Plain suggests native herbaceous habitats might be limiting during autumn in these regions, whereas lack of response in the Eastern Tallgrass Prairie, Central Hardwoods, and central Texas regions suggests that herbaceous habitat either was not limiting or buffers failed to provide adequate requirements for bobwhites during autumn. Selection of other habitats to meet security and thermoregulatory needs might have resulted in lack of response in these regions. Native herbaceous cover provided by buffers can provide critical habitat in row‐crop agricultural systems in some regions, and can contribute to regional population recovery objectives of the Northern Bobwhite Conservation Initiative (NBCI). However, range‐wide NBCI recovery objectives will best be met through multiple conservation practices in row‐crop agricultural systems. © 2013 The Wildlife Society.

Response of non‐grassland avian guilds to adjacent herbaceous field buffers: testing the configuration of targeted conservation practices in agricultural landscapes

“…; Evans et al . ). Buffered agricultural fields were selected randomly from a sampling frame of CP33 contracts in each participating state ( n ≥ 40 per state).…”

Edge Effects on Avian Diversity and Density of Native Grass Conservation Buffers

“…Dickcissels are grassland specialists found frequently on CRP land [27,28]. Dickcissel density in buffers adjacent to developed areas did not differ from buffers adjacent to grassland habitat.…”

Improving distance sampling: accounting for covariates and non‐independency between sampled sites

“…Evans et al . ). Conover, Burger & Lindner () showed that field buffers increased nesting activities along field margins for a range of birds, including indigo buntings.…”

“…The National CP‐33 Monitoring Program coordinated by the Mississippi State University, Department of Wildlife, Fisheries, and Aquaculture was set up to monitor beneficial effects of herbaceous buffers around agricultural fields on bird densities in several Southeastern and Midwestern states (Evans et al . ). To set up a monitoring scheme, a minimum of 40 CP‐33 contracts per state were randomly selected from all CP‐33 contracts.…”