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Publication Date

12-1-2011

Abstract

Tanglehead grass (Heteropogon contortus; hereafter tanglehead) has historically occurred in small, isolated patches across south Texas. During the past 10–15 years, however, tanglehead has undergone a rapid expansion in south Texas similar to the spread of other introduced exotic grasses. Tanglehead can form extensive and exceptionally dense stands of grass that may result in reduced usable habitat space for the Northern Bobwhite (Colinus virginianus; hereafter bobwhite) in south Texas. Our objectives were to assess how the presence of vast and dense areas of tanglehead influenced nesting and general habitat use by bobwhites on south Texas rangelands. We monitored bobwhite nesting and general (off-nest) habitat use with radio telemetry during the 2008 and 2009 breeding seasons (April–September) at a private ranch in Duval County, Texas. We sampled bobwhite habitat at nest locations, random locations, and organism-centered locations. We analyzed habitat data at the macrohabitat (between habitat patches) and microhabitat (within habitat patches) scales for both nest site use and general (organism-centered) habitat use when bobwhites were off the nest. Nest sites had an average of 23.4% more tanglehead cover than random locations. Bobwhites nested in tanglehead but did not use tanglehead in greater proportion than available at the macrohabitat scale. In the organism-centered habitat use comparisons with random locations, bobwhites also did not significantly use or avoid tanglehead at the macrohabitat scale. However, when off-the-nest, bobwhites typically used patches of vegetation that had 38% less tanglehead cover compared to random locations. Our conclusions are that while bobwhites nest in patches of tanglehead at the macrohabitat and microhabitat scales, they tend to avoid areas with dense tanglehead cover at the microhabitat scale during the course of their other daily habitat use patterns. This avoidance of dense tanglehead patches for off-nest daily activities may be related to decreased plant diversity and presumably lack of available food.

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