What was done
The authors set out to test the hypothesis that survival rates of a Mediterranean waterbird - Cory's Shearwater - would be negatively affected by warmer El Niņo conditions.  To accomplish their design, the authors used a number of statistical analyses on the capture histories of a small population of breeding birds in two caves on the Italian Tremiti Islands over the period 1988 to 1998.

What was learned
The authors found there was a statistically significant difference in bird survival rates between La Niņa (cooler) years and non-La Niņa (warmer) years.  In contrast to their original hypothesis, they determined that survival rates during strong El Niņo (warmer) years were greater or "the inverse of what we expected."  As for the reason why bird mortality rates were highest during La Niņa years, the authors suggest this phenomenon results from a related La Niņa influence on Atlantic hurricanes, which tend to be more numerous in La Niņa vs. El Niņo years.  Such a relationship was confirmed by the authors in two additional statistical tests using data on bird mortality rates and the number of intense hurricane days.

What it means
The central finding of this paper is just another indication of the simple fact that - in most cases - warmer is better, even for the birds!