SANTA CRUZ, CA--Seabird colonies on islands are highly vulnerable to introduced rats, which find the ground-nesting birds to be easy prey. But the ecological impacts of rats on islands extend far beyond seabird nesting colonies, according to a new study by researchers at the University of California, Santa Cruz.
The study, which will be published the week of February 25, 2008, in the Proceedings of the National Academy of Sciences, has already helped make the case for the first major rat eradication effort in the Aleutian Islands. Planned to begin this summer, the project will target rats on the appropriately named Rat Island.
The UCSC researchers found that the presence of rats on islands in the Aleutian Archipelago dramatically alters the intertidal zone, reducing the amount of seaweed and increasing the numbers of snails, barnacles, and other invertebrates. These changes result from the decimation of seabird populations by the rats, according to graduate student Carolyn Kurle, who led the study.
"When you're on an island with rats, there are so few birds it's silent, in contrast to the cacophony on the islands without rats," Kurle said.
Some of the affected birds--sea gulls and oystercatchers, in particular--are major predators of invertebrates in the intertidal zone. In their absence, the snails, limpets, and other grazers increase in abundance, eat more algae, and clear more space for other invertebrates to settle and grow. The result is a shoreline practically stripped bare of the usual cover of fleshy algae (i.e., seaweed).
"Where there are no rats, we found plenty of birds, fewer invertebrates, and a lot more algal cover," Kurle said.
Kurle's coauthors are associate professor Donald Croll and assistant adjunct professor Bernie Tershy of UCSC's Department of Ecology and Evolutionary Biology. Croll and Tershy are also the cofounders of Island Conservation, a nonprofit organization dedicated to the
|Contact: Tim Stephens|
University of California - Santa Cruz