Relative Abundance of Adult and Juvenile Marbled Murrelets in Prince William211 Sound, Alaska: Developing a Productivity Index. Restoration Project 95031. EXXON 211 VALDEZ Oil Spill Restoration Project Final Report

摘要

To monitor the reproductive success of marbled murrelets (Brachyamphus211u001emarmoratus), the authors investigated a productivity index that uses at-sea 211u001ecounts of hatching-year (HY) birds and after-hatch-year (AHY) birds. The authors' 211u001eobjectives were to define seasonal patterns of abundance by age class and develop 211u001ea protocol for estimating productivity. The authors integrated a 1994 pilot study 211u001ewith replicate surveys of 6 sites in Prince William Sound in summer 1995. At all 211u001esites, numbers of AHY birds peaked in late July and declined throughout August, 211u001ewhereas HY birds increased after 28 July and peaked by 9 August. As a result, the 211u001epercentage of juveniles increased; thus, HY density may be a better index than 211u001ejuvenile: adult ratios because of migration by post-breeding adults. HY densities 211u001ewere highly correlated with June AHY densities, suggesting that the June 211u001ePopulation reflects the number of locally breeding birds. The regression of June 211u001eAHY vs. July-August HY counts may also index regional murrelet reproductive 211u001esuccess.