Top down versus bottom up: What affects common murres the most?

Julia Parrish
University of Washington

Wednesday, August 12, 1998
3:30 p.m.—Pacific Forum

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Seabirds are a long- lived, low-fecundity species which usually display a high degree of natal philopatry. From a population point of view, this means that agents increasing adult mortality are much more likely to have a noticeable affect on the population than agents affecting reproductive success. However, the real world is often far more complicated than theory would suggest.

For the past nine years, I have studied the factors affecting the size and success of a population of common murres (Uria algae), nesting on the last remaining breeding colony in Washington State—Tatoosh Island. On this colony, success or failure is a fascinating mixture of ecology (as in the availability of food and the degree of predatory pressure), and conservation (as in the chance of an oil spill or the fate of murres foraging in areas frequented by gillnetters). Further complications arise when the indirect as well as direct effects of various mortality and reproductive factors are considered. For instance, although the dominant predator in the system, bald eagles, (Haliaeetus leucocephalus), do exert a measurable direct effect (they eat murres), their indirect effect (they scare murres) can result in near total breeding failure. And of course, one can never forget the long shadow of El Niņo.

In this seminar, I will review what we think we know about murres, hint strongly that studying behavior is crucial to any sort of understanding of population and community-level patterns, and suggest ways we might marry behavior and conservation to the benefit of populations affected by a myriad of natural and human-induced factors.

Next: A closer look at U.S. marine science and policy programs

 Last updated: December 19, 2000