Date of Award

8-2012

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Committee Chair

Frank Moore

Committee Chair Department

Biological Sciences

Committee Member 3

Wylie Barrow

Abstract

Few studies have considered the impact of weather events on migratory birds during stopover, and essentially none on how hurricanes affect their stopover biology during spring passage. About two thirds of eastern North American forest breeding bird species migrate twice annually between temperate breeding areas and subtropical and tropical wintering grounds, and movement in relation to the Gulf of Mexico (GOM) is a conspicuous and important part of that migration system. During inclement weather or winds inconsistent with travel direction, migratory birds oft.en/a/lout and concentrate by the thousands in forest patches that occur along the northern coast of the GOM. Anthropogenic change, hurricanes, sea level rise, and coastal subsidence have greatly reduced the amount of coastal forest in this region, which may affect the stopover biology of migratory birds. In southwestern Louisiana, coastal cheniere forests are the first possible landfall for birds returning north in spring after a nonstop flight (18-24 hr) of greater than 1,000 km. Since chenieres serve as important stopover sites for migratory birds, disturbances that alter them may affect the ability of migrants to replenish important fuel stores to continue migration. This region was severely impacted by two recent hurricanes, Rita in 2005 and Ike in 2008. For this thesis I assess the impact of these storms on spring migrants at two levels: (1) abundance of birds with similar foraging strategies (i.e. foraging guilds) and (2) stopover biology, including fuel deposition rates, of individual migrants. To do so I utilize long-term data collected on migratory birds at a study site near Johnson Bayou, which was directly impacted by both storms. Species were classified into foraging guilds based on the vertical height (i.e. canopy/subcanopy, understory, and ground) and foraging substrate (e.g. live foliage, leaf litter) where birds were typically observed in chenieres during spring migration. Bird mist net capture data, avian transect data, and vegetation survey data collected pre- and post-hurricane were examined for changes in response to storm damage to stopover habitat. Capture data were also used to assess whether stopover duration (SD) and fuel deposition rate (FDR) differed pre- and post-storm for species representatives from different foraging guilds. Live foliage-gleaning canopy foragers decreased post-storm compared to pre-storm levels yet canopy airspace foragers increased after each storm, significantly after Hurricane Ike (p<0.01). Arthropod-foraging understory species decreased with each storm and frugivorous understory species increased after Hurricane Rita. Ground foraging species that feed in open, grassy areas increased, whereas leaflitter foraging species decreased. Although both storms had major impacts on vegetative structure, SD and FDR did not differ in line with guild-specific storm-response expectations. Migrant abundance by guild pre- and post-storm changed as expected, but in most cases the differences were not consistent across all guild members. Even in a disturbed landscape migrants appear flexible in their use of habitat and foraging behavior, which may not be surprising in light of the variety of habitats and food resources intercontinental migrants encounter during migration.

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