Effects of Deepwater Horizon Crude Oil on the Flight Performance and Behavior of Avian Species: The Homing Pigeon (Columba livia) as a Model
AuthorPerez, Cristina Rene
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Avian species are among the most greatly impacted following oil spill events. The acute effects on birds heavily covered in oil are well documented. Less understood are the sub-lethal effects of oil contamination. Particularly, the sub-acute effects of oil exposure on feather function. Feather functions such as insulation, buoyancy and flight are made possible by the precise microstructure of feathers and application of oils from the uropygial gland through preening. Crude oil transfer to bird feathers disrupts their microstructure by causing the barbs and barbules to clump together. The compromised feather structure affects feather functions such as flight. It is obvious that heavily oiled birds cannot fly. However, the presumption that lightly oiled birds are uninjured warrants investigation. The Deepwater Horizon (DWH) oil spill in 2010 was unique in that many oiled birds survived the oil spill with light or trace amounts of oiling. Consequently, studies designed as part of the DWH Natural Resource Damage Assessment focused on the effects of low-level oil exposure. Particularly, a suite of studies was designed to investigate the effects low-level oil exposure has on avian flight. Experiments on oil-induced flight effects have not been previously conducted and the results from these studies were novel. In this research, homing pigeons (Columba livia) were used as surrogate species to assess the effects external oil on the wings and tail feathers have on flight performance and behavior. One of the objectives was to determine the flight effects resulting from a single oil application of 20% surface area coverage at flight distances of 81 and 161 kilometers. Using GPS data loggers, flight duration analyses were performed and indicated a significant increase in flight duration after a single exposure in birds flying 81 and 161 kilometers. The greatest flight performance effect occurred on the day of oiling, but was maintained over experimental flights. The increase in flight duration was a result of changes in behavior during flight. Namely, oiled birds had significantly longer en route stopping times, consequently taking longer to return to the loft. Increasing the flight distance and subjecting oiled birds to different geographical landmarks had profound impacts on their flight behavior. Data from GPS data loggers showed that oiled birds changed their flight paths, notably flying closer to a mountain ridge, while increasing their actual flight distance and decreasing their homing efficiency. We believe these behaviors were employed to cope with flying with oiled feathers and to reduce flight costs. We also examined the effects of multiple oil exposures on flight and associated weight change of birds flying 137 km. The birds in this study were oiled 5 times and showed significantly increased flight duration. Additionally, these birds lost more weight during flights and did not regain the weight they lost between flights, resulting in overall weight loss and poor body condition in comparison to unoiled birds.The results from these studies provide initial understanding of how light oil exposure impacts free-flying birds. The sub-acute flight impacts from oil exposure are likely to be substantial and manifest at the exposed bird population level through reduced survival and reproduction. Thus, the presumption that lightly oiled birds that leave the site of contamination are unharmed is incorrect and should be considered when quantifying avian injury after oil spill events. The results from these studies have important implications for the fate of migratory birds that were lightly oiled during the DWH oil spill.