Productivity of waterbirds in potentially impacted areas of Louisiana in 2011 following the Deepwater Horizon oil spill

The Deepwater Horizon oil spill (2010) could have affected the behavior and productivity of birds nesting along the Gulf of Mexico. This research examined the productivity of several species of colonial waterbirds in 2011 in LA colonies that were classified according to the M252 peak SCAT shoreline map oiling designations (as of April 6 2011) within 2 km of each colony. Colonies were classified as no oil, little oil, or medium to heavy oil. Because of the uneven distribution of oil and variation in bird composition within colonies, not all species occurred in each of the three oiling classes in the LA colonies studied. I tested the following hypotheses: (1) there were no interspecific differences in nesting phenology, (2) there were no differences in the number of species per colony as a function of oiling, and (3) there were no differences in reproductive measures as a function of oiling. Nesting phenology differed among species, with brown pelicans (Pelecanus occidentalis), great egrets (Ardea alba), and tri-colored herons (Egretta tricolor) nesting earlier than the other species. There were no significant differences in the number of species nesting in colonies as a function of oiling category. Along LA's shoreline, nests in colonies with a "no oil" category within 2 km of the colony had similar or lower maximum number of chicks/nest, than those from birds in colonies designated as light or moderate/heavy oiling. Average maximum chick sizes in nests in colonies designated as no oil were either similar to or smaller than chicks in nests in colonies designated as either category of oiled. The data suggest that in the year following the oil spill, there were no differences in reproductive success. Although long-term studies are essential to determine effects on population dynamics, the continued exposure of birds nesting along the Gulf of Mexico to acute and chronic oil sources make this a nearly impossible task.