When is a species extinct?

January 12, 2009

Many thousands of hours have been spent over the past four field seasons combing hardwood forests and swamps for the Ivory-billed Woodpecker. But how long and how hard must you search before you can declare with near-certainty that a creature is truly gone forever? Authors from the University of Idaho, Oregon State University, the Cornell Lab of Ornithology, Point Reyes Bird Observatory and Tufts University approach this dilemma in mathematical terms. Their finding are published in the December 2008 issue of Avian Conservation and Ecology.

The authors use the ivory-bill search in Arkansas and searches for eight species of endangered Hawaiian forest birds to formulate their conclusions. Factors that must be considered in both cases are the probable size of the population, availability of habitat, type of habitat, weather, observer skills, and much more.

The authors conclude the probability of finding an ivory-bill in the primary study area in eastern Arkansas is just 12% if there is only one bird, 49% if there are five birds, and 74% if there are 10 birds, based on the amount of territory searched during the 2004-05 and 2005-06 field seasons. Likewise, they say efforts made to date to locate endangered Hawaiian forest birds have not been sufficient to declare with certainly that certain species no longer exist.

“Declaring a species as extinct or delisting a species where legal protection exists is a poor idea unless statistically sufficient survey efforts have been made,” they conclude.


Read the entire paper here