Why Do Marbled Murrelets Attend Old-Growth Forest Nesting Areas Year-Round?

Abstract

The attendance of Marbled Murrelets (Brachyramphus marmoratus) in old-growth forest in central California was studied from January 1989 through July 1991. Five nesting areas were surveyed (n = 216 survey mornings) by recording the number of times murrelets were detected (by sight or sound) during a 2-h period at dawn. Presence or absence of murrelets was determined during an additional 123 morning surveys. Murrelets were active in nesting areas nearly year-round. Detection levels in fall and winter (nonbreeding season) were about one-half those in spring and summer (breeding season). Murrelets were absent, or detections were minimal and most variable, during August-October and March. These transitional periods of low murrelet activity coincided with periods of molt. Detection levels were least variable in November and December. Marbled Murrelets in central California attended nesting areas during the nonbreeding season more frequently than murrelets in other regions, and more often than most other alcids. Wintering murrelets may be year- round resident breeders and attendance during the nonbreeding season may be important for maintenance of nest sites, nesting territories, or pair bonds. Nesting areas should be managed throughout the year. Winter may be an ideal time to conduct long-term monitoringstudies, as variability in attendance is low.