Deepwater Horizon crude oil reduces aerobic capacity of birds

Crude oil spills can have catastrophic effects on marine and inland ecosystems, yet it is difficult to accurately quantify the extent of ecological damage caused by oil spills. For instance, avian population damage assessments conducted after large oil spills (e.g., Deepwater Horizon spill) often focus on the number of visibly oiled birds. However, birds without visible oiling can exhibit hematological damage from oil ingestion. If such hematological responses limit oxygen deliver to tissues and impair aerobic performance, then energy-mediated effects from oil ingestion may ultimately affect endpoints of demographic significance (e.g., survival and reproduction). We investigated whether oil ingestion affects aerobic performance in birds by orally dosing zebra finches (Taeniopygia guttata) with 2 or 6 mL/kg of weathered MC252 crude oil for 28 days. After 14 and 28 days of dosing, we measured hematological indices (oxidative damage, packed cell volume [PCV], hemoglobin, reticulocytes), maximum metabolic rate (MMR), resting metabolic rate (RMR), and short-distance flight performance. Finches exposed to oil exhibited lower hemoglobin and PCV, higher reticulocyte counts, and greater oxidative damage. Shifts in these hematological indices appeared to alter organismal energetics, resulting in reduced MMR, RMR, and aerobic scope. Short-distance burst-flight was not negatively impacted by oil ingestion. Collectively, these results suggest oil ingestion impairs metabolic performance, which may negatively impact a birds ability to perform sustained energetically expensive activities (e.g., migration). SignificanceThe 2010 Deepwater Horizon oil spill released an unprecedented volume of crude oil (MC252) into the northern Gulf of Mexico and contaminated 2100 km of shoreline habitat that serves as critical breeding grounds and migratory stop-over sites for birds. Here we describe the impact of oil ingestion on the aerobic capacity of zebra finches, a model songbird. Oil ingestion reduced maximum metabolic rate and aerobic scope, which may be caused in part by hematological damage. These data suggest oil ingestion limits the ability of birds to perform essential energetically demanding activities (e.g., migration, nest incubation), thus quantification of avian injury based on external oiling alone may underestimate the true impact of oil spills on avian populations.