Using geographic information systems to compare non-uniform marine bird surveys: Detecting the decline of kittlitz's murrelet (brachyramphus brevirostris) in Glacier Bay, Alaska

Abstract

Kittlitz's Murrelet (Brachyramphus brevirostris) is a rare seabird whose populations are concentrated in glaciated areas of Alaska. Declines in some parts of its range have led to increased concern over population viability. The remote and cryptic nesting habits of Kittlitz's Murrelets, in contrast to colonial seabirds, preclude monitoring their populations at nest sites and necessitate use of at-sea surveys to count birds. We compared surveys for seabirds in Glacier Bay, Alaska, during 1991, 1999, and 2000, to identify trends in the local Kittlitz's Murrelet population. The surveys conducted in 1999-2000 covered much of the same habitat as those conducted in 1991 but differed in aspects of survey design (i.e., start and stop points, navigation methods, and amount of offshore sampling). We developed a technique using a geographic information system to extract and recompile data from the 1999-2000 surveys that allowed spatially "matched" comparisons with the 1991 survey transects. This comparison of using "matched" transects indicated that the Kittlitz's Murrelet population in Glacier Bay had declined by 83% between 1991 and 1999-2000. Our analytical approach may be useful in similar situations in which current and historical surveys are not spatially uniform, particularly where there is a strong spatial component to the species distribution. © The American Ornithologists' Union, 2008.