Sublethal Effects of Crude Oil Exposure Alter Population-Level Responses in an Individual Based Model of a Passerine Bird.

Although large oil spills cause intense ecological damage and receive heavy media and research attention, small spills occur much more frequently and have ecological consequences. Currently, assessment of damage to wildlife after oil spills of any magnitude primarily involves carcass counts and observation of individuals with visible oiling. Such methods do not account for sublethal or non-visible oil exposures that accompany the consumption of contaminated prey or soils. Recent research demonstrates that mild oil exposure can affect time-energy budgeting in birds, as they alter foraging and preening time, and metabolic rates. There is a need to understand how both frequency and length of exposure (duration) to oil spills interact with mechanisms of lethality and sublethality to affect population declines and recoveries. We developed a dynamic energy budget individual-based model to represent a generalized altricial bird and simulate the outcomes of various oiling scenarios. The models revealed that sublethal effects of oil exposure are important to population decline and recovery because they altered trajectories of population recovery through reduced fecundity and embryo survival. Our models also indicate that small oil spills can have significant effects on populations, particularly when spills occur frequently or persist in the environment. Our findings agree with empirical studies showing that sublethal effects of oil exposure in birds are important to population dynamics and indicate that frequent or long-lasting small spills can have significant effects on populations. Minimizing frequency and prioritizing expeditious clean-up of all, including small, spills could result in better conservation outcomes.