Selection of forage-fish schools by Murrelets and Tufted Puffins in Prince William Sound, Alaska

Abstract

We collected hydroacoustic and bird-observation data simultaneously along transects in three areas in Prince William Sound, Alaska, 21 July-11 August 1995. The probability of the association of fish schools with Marbled Murrelets (Brachyramphus marmoratus) and Tufted Puffins (Fratercula cirrhata) was determined through the use of resource selection functions based on logistic regression. Mean (± SD) group sizes were small for both species, 1.7 ± 1.1 and 1.2 ± 0.7 for Marbled Murrelets and Tufted Puffins, respectively. Oceanographically, all study areas were stratified with synchronous thermo- and pycnoclines (a water layer of increasing temperature and density, respectively, with increasing depth). Our analysis indicated that Tufted Puffins selected fish schools near their colony, whereas Marbled Murrelets selected smaller, denser fish schools in shallower habitats. We suggest that murrelets selected shallower habitats in response to lower maximum diving depths than puffins. Small feeding-groups size is discussed in terms of foraging theory and as a consequence of dispersed, low density food resources.