Use of Treeless and Forested Habitat by Marbled Murrelets in South-Central Alaska

Abstract

--Although the Marbled Murrelet (Brachyramphus marmoratus) usually nests in mature coniferous trees throughout most of its range, in south-central Alaska Marbled Murrelet nests have been found on the ground in unforested areas as frequently as they have been found in older-aged forests. Because ground nests are typically found serendipitously, the relative occurrence of ground nesting is unknown. Further, the importance of unforested habitat to nesting murrelets is unknown. Comparing murrelet dawn activity (related to breeding activity) in forested and unforested habitats in the Kenai Fjords National Park, Alaska inJuly, 1993, we found that the number of inland murrelet was appreciably and significantly higher in forested than in unforested habitat (forested stations: x = 48.1 detections per station, SE + 7.7; unforested stations: x = 17.4, SE ? 4.0). Visual observations of murrelets flying close to the ground or trees are indicators of nesting, and were much more frequently observed in forested areas. Within unforested areas, murrelet land-use may be related to the amount of low vegetation and shrubs, as stations with more vegetation had higher dawn activity. These data suggest that, although Marbled Murrelets nest on unforested ground in south-central Alaska, forested habitat is much more heavily occupied than unforested habitat. We propose that habitat devoid of older-aged coniferous forest is suboptimal due to the shortage of nest sites that are as protected from predators and weather as those provided by the 3-dimensional structure of mature trees and older-aged forests. Received 4 May 2000, accepted 30July 2000.