Effects of the Iron Baron oil spill on little penguins (Eudyptula minor). III. Breeding success of rehabilitated oiled birds

The long-term effects of oiling on the breeding success of rehabilitated oi led little penguins (Eudyptula minor) were examined over two consecutive br eeding seasons following the Iron Baron oil spill in 1995. The commencement of egg laying was delayed among rehabilitated oiled penguins compared with non-oiled birds during the 1995/96 breeding season. During that season, ha tching success (number of eggs hatched from those laid) was no different in nests containing rehabilitated oiled penguins than in those containing non -oiled birds, but overall egg success (number of pre-fledging chicks from t he number of eggs laid) was significantly lower among rehabilitated oiled b irds. This effect was predominant in nests containing a rehabilitated oiled female, where the probability of successfully fledging any chicks was 22% lower than in nests containing a non-oiled female. During the 1996/97 breed ing season, there was no significant difference between either the hatching or egg success of rehabilitated oiled penguins and non-oiled birds. In bot h seasons, the pre-fledging masses of chicks from rehabilitated oiled pengu ins were significantly lower than those from non-oiled birds. The chicks of rehabilitated oiled penguins were therefore expected to have lower surviva l than chicks raised by non-oiled parents. Results indicate that oiling not only reduced the number of chicks raised by rehabilitated oiled penguins i n the short term, but also decreased the quality of young produced for at l east two seasons following the spill.