Antibacterial and anatomical defences in an oil contaminated, vulnerable seaduck

Oil-spills have killed thousands of birds during the last 100 years, but
non-lethal effects of oil-spills on birds remain poorly studied. We
measured phenotype characters in 279 eiders Somateria mollissima of which
13.6% were oiled. We tested the hypotheses that (1) the morphology of
eiders does not change due to oil contamination; (2) the anatomy of organs
reflects the physiological reaction to contamination e.g. increase in
metabolic demand, increase in food intake and counteracting toxic effects
of oil; (3) large locomotion apparatus that facilitates locomotion
increase the risk of getting oiled; and (4) individual eiders with a
higher production of secretions from the uropygial grand were more likely
to have oil on their plumage. We tested whether 19 characters differed
between oiled and non-oiled individuals, showing a consistent pattern. The
final model retained seven predictor variables showing relationships
between eiders contaminated with oil and food consumption, flight and
diving abilities. We tested whether these effects were due to differences
in body condition, liver mass, empty gizzard mass or other characters that
could have been affected by impaired flight and diving ability. There was
no evidence of such negative impact of oiling on eiders. We found that
significant exposure to oil was associated with increased diversity of
antibacterial defence. Oiled eiders did not constitute a random sample,
and superior diving ability as reflected by large foot area were at a
selective disadvantage during oil spills. Thus, specific characteristics
predispose eiders to oiling, with an adaptation to swimming, diving and
flying being traded against the costs of oiling. In contrast, individuals
with a high degree of physiological plasticity may experience an advantage
because their uropygial secretions counteract the effects of oil
contamination. --