Master of Science (MS)
Renewable Natural Resources
The Henslow’s Sparrow (Ammodramus henslowii) is the fastest declining short-distance migrant and fastest declining grassland bird in North America. Declines in longleaf pine (Pinus palustris) savannas, its primary wintering habitat, have exceeded 97%. Other than basic habitat requirements, very little is known about its wintering ecology. I examined habitat associations of wintering Henslow’s Sparrows resulting from fire in longleaf pine savannas in southeastern Louisiana during two winters. Because it is important to understand the relative importance of habitat parameters, which include structure, species composition, and food availability, I measured these to determine their relative importance to Henslow’s Sparrow densities. I aged birds to understand the effects of fire on age-specific distributions and body condition, employed a mark-recapture analysis to determine over-winter survival, and determined over-wintering home ranges starting when Henslow’s Sparrows first arrived in October until they departed in April. Bird density was higher in savannas burned during the previous growing season (“burn-year”) than in savannas burned two growing seasons before (“non-burn-year”) in a two-year fire rotation scenario. Burning caused plant species compositions to shift from a Rhychospora spp. dominated habitat to an Andropogon/Schizachyrium spp. dominated habitat, however, total seed availability was not significantly different between burn-year and non-burn-year savannas. Because habitat-mediated age distributions, body condition, and home range size were also not significantly different between fire treatments, these findings are consistent with the idea that wintering Henslow’s Sparrows are generalist foragers. Bird density was best predicted by habitat structure, specifically reduced ground-level herbaceous vegetation and fewer shrubs. A higher survival probability was detected in burn-year savannas and may be responsible for habitat selection in this species. It is not clear how Henslow’s Sparrows locate apparently high quality habitat due to unpredictable changes from one year to the next. I therefore determined the extent of post-migration movements and between-year site fidelity. There was evidence of post-migration movements, while nine of 154 birds exhibited between-year site fidelity, suggesting that a variety of spatial use strategies occur in this population. Land managers can manipulate savanna structure through frequent growing-season prescribed fires, which are critical to Henslow’s Sparrow conservation.
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Johnson, Erik Ivan, "Effects of fire on habitat associations, abundance, and survival of wintering Henslow's Sparrows (Ammodramus henslowii) in southeastern Louisiana longleaf pine savannas" (2006). LSU Master's Theses. 3339.
Philip C. Stouffer