Habitat and landscape effects on abundance of Missouri's grassland birds

Abstract

Of 6 million ha of prairie that once covered northern and western Missouri, <36,500 ha remain, with planted, managed, and restored grasslands comprising most contemporary grasslands. Most grasslands are used as pasture or hayfields. Native grasses largely have been replaced by fescue (Festuca spp.) on most private lands (almost 7 million ha). Previously cropped fields set aside under the Conservation Reserve Program (CRP) varied from a mix of cool-season grasses and forbs, or mix of native warm-season grasses and forbs, to simple tall-grass monocultures. We used generalized linear mixed models and distance sampling to assess abundance of 8 species of breeding grassland birds on 6 grassland types commonly associated with farm practices in Missouri and located in landscapes managed for grassland-bird conservation. We selected Bird Conservation Areas (BCAs) for their high percentage of grasslands and grassland-bird species, and for <5% forest cover. We used an information-theoretic approach to assess the relationship between bird abundance and 6 grassland types, 3 measures of vegetative structure, and 2 landscape variables (% grassland and edge density within a 1-km radius). We found support for all 3 levels of model parameters, although there was less support for landscape than vegetation structure effects likely because we studied highpercentage-grassland landscapes (BCAs). Henslow's sparrow (Ammodramus henslowii) counts increased with greater percentage of grassland, vegetation height-density, litter depth, and shrub cover and lower edge density. Henslow's sparrow counts were greatest in hayed native prairie. Dickcissel (Spiza americana) counts increased with greater vegetation height-density and were greatest in planted CRP grasslands. Grasshopper sparrow (A. savannarum) counts increased with lower vegetation height, litter depth, and shrub cover. Based on distance modeling, breeding densities of Henslow's sparrow, dickcissel, and grasshopper sparrow in the 6 grassland types ranged 0.9-2.6, 1.4-3.2, and 0.1-1.5 birds/ha, respectively. We suggest different grassland types and structures (vegetation height, litter depth, shrub cover) are needed to support priority grassland-bird species in Missouri. ß 2011 The Wildlife Society.

Management factors affecting densities of common grassland birds of high elevation grasslands of eastern South Africa: Ingula as a case study

“…Overall, Azpiroz and Blake (2016) found that bird numbers were more correlated with grass cover than with grass height in contrast to observations of Henslow's Sparrow (Ammodramus henslowii) at modified Missouri grasslands (e.g. Jacobs et al 2012). But this is because the comparison of Azpiroz and Blake (2016) was made with croplands where vegetation height tends to be higher but sparse.…”

“…Depending on the intensity of fire and grazing, heterogeneity of micro niches is created across the landscape that affects bird species densities differently. The impact of fire and grazing on landscape and habitat attributes has been well documented (Jacobs et al 2012). Our study is the first in the region to examine how vegetation variables affect the density of birds in a hierarchical way that incorporates detection.…”

“…Most species of conservation concern are found on privately owned farms where application of fire and grazing is mostly variable (Howell et al 2009;Hanley et al 2012;Jacobs et al 2012;Ciuzio et al 2013). In these differently managed lands, we suggest that measurements of vegetation variables be limited to grass height and cover because these are the key habitat variables that are mostly associated with habitat use by birds (Fisher and Davis 2010;Hovick et al 2014) and doing so also allows survey efforts to cover a large area in a short space of time.…”

Quantifying avian relative abundance and ecosystem service value to identify conservation opportunities in the Midwestern U.S.

“…Core patches and their surrounding matrix can be thought of as conservation or management units, for example, when a core is a protected area. GBCAs have been identified in the Prairie Pothole Region of the U.S. (Johnson et al 2010), and in the states of Missouri and Iowa (Jacobs et al 2005(Jacobs et al , 2012. Surprisingly, bird observations are not used to identify or rank GBCAs because the identification process occurs at scales larger than available observational data.…”

Vegetation maps based on remote sensing are informative predictors of habitat selection of grassland birds across a wetness gradient

“…Yet, differences were usually described for a larger range of ecological 383 conditions (Jacobs et al, 2012). It is thus particularly interesting to observe that it is possible to 384 determine species-specific habitat selection profiles within a much narrower ecological range.…”