The coastline of the northern Gulf of Mexico (NGOM) represents important non-breeding habitats for 28 species of migratory shorebirds. As processes of climate change accelerate, these habitats are expected to experience dramatic land loss. In addition, the NGOM has experienced several natural and human mediated disasters over the last decade, including Hurricane Katrina and the Deepwater Horizon Oil spill (DWH). Predicting the impacts of these events requires an understanding of the interactions between shorebirds and their habitats. However, the migration ecology of shorebirds on the NGOM has not been well studied. To better understand the effects of the DWH and the importance of NGOM habitats to the migration ecology of shorebirds I carried out two related studies. First, I investigated the potential for long term, large-scale effects of oil exposure to migratory shorebirds through both a literature review, and by investigating the exposure to DWH oil in seven species of shorebirds that winter or stopover along the NGOM. I found that through migratory carry-over effects, oil spills and other environmental disasters, have the potential to impact ecosystems far from the event. Exposure results suggest as many as 1 million shorebirds were impacted by direct exposure to oil, and many more may have been negatively affected by disturbance from cleanup activities in oiled habitats. Second, I investigated the migration ecology of three near-arctic breeding species of shorebirds (Semipalmated sandpipers (Calidris semipalmatus), Western Sandpiper (C. mauri) and Dunlin (C. alpina), by measuring within- and among-species variation in habitat use, stopover duration, and refueling rates, as measured by plasma metabolites, across 3 habitat types. I found that among species, shorebirds vary in their migration ecology according to the distance to the next stopover site, suggesting NGOM habitats may be particularly important to longer-distance â"u20acœjumpâ"u20acù migrants (Dunlin). I also found that while shorebirds are found across all habitat types sampled, the back bay habitats of barrier islands provided a higher quality habitat (as evidenced by higher prey biomass, and a higher refueling rate) than traditional coastal mudflats or remnant wetlands, highlighting the importance of considering shorebird ecology in barrier island restoration plans. / 1 / Jessica Renee Henkel

Distributional and ecological dynamics of Neotropical migratory birds at stopover sites where they maintain critical fat reserves during migration remain poorly understood in North American aridlands. I examined spatiotemporal abundance and timing of migrants relative to 1) upland and riparian habitats, 2) post-fire landscape mosaics, and 3) phenological synchrony and overlap of migration with tree flowering in southeastern Arizona's Madrean Archipelago (2009-2011), and 4) abundance, habitat breadth, and foraging substrates relative to tree flowering along the Colorado River in southwestern Arizona and northwestern Sonora, Mexico (2000-2003). I explored these dynamics relative to local weather conditions and El Niño Southern Oscillation (ENSO) climate phenomena. In Madrean habitats, migrants showed three non-exclusive responses to high precipitation, snowfall, and low minimum temperatures associated with El Niño in 2010; migration timing adjustments, habitat shifts, and reduced abundances suggesting migration route shifts. Foliage-gleaning insectivores were most abundant in high severity burns, disproportionate to their availability, and decreased with time since fire (TSF); flycatchers were most abundant in low-moderate severity and increased with TSF. Migrant abundance increased with tree flowering. Phenological overlap declined with increasing difference in timing of these events. Overlap was lowest in 2011 in riparian habitat due to low willow (Salix goodinggii) flowering, despite high migrant abundance, but lowest in 2010 in montane conifer, despite high pollen cone production by Douglas-fir (Pseudotsuga meziesii), suggesting temperature limitation of insect abundance at high elevations, but water limitation of plant phenology at lower elevations. Along the Colorado River, migrant abundance and habitat breadth had inverse positive and negative quadratic relationships, respectively. Abundance increased with tree flowering, but only in 2003 during severe drought. Habitat breadth increased with monsoon precipitation. Foraging substrate use tracked flowering, shifting from willow to mesquite (Prosopis sp.); the overlap coincided with peak abundance and narrowest habitat breadth. Maintenance of diverse vegetation and post-fire landscape mosaics in the Madrean Archipelago should benefit migratory bird diversity. Flowering phenology likely provides large-scale cues of local-scale stopover habitat condition associated with interannual climatic variation. Management and restoration of upland habitats and large riparian woody perennials will be critical for migratory bird conservation in aridlands.

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