Activity patterns of Marbled Murrelets in Douglas-Fir old-growth forests of the Oregon Coast Range

Abstract

We monitored activity patterns of Marbled Murrelets (Brachyramphus marmoratus) on a near-daily basis using audio-visual surveys during three breeding seasons at five forest stands in the Oregon Coast Range. Three measures of activity were recorded: number of daily detections, number of daily vocalizations, and duration of daily activity. Each measure was highly variable within and among stands and years, and we recorded greater variability than has been previously reported for this species. The three measures of activity were strongly correlated within a day at each survey station, but correlative relationships at temporal and spatial scales greater than this were inconsistent. Activity varied greatly from one day to the next during all portions of the breeding season, and we did not identify any month when variability in activity was consistently higher or lower than any other month. Multivariate analyses revealed that weather and date variates explained little of the variability in daily activity. Given the extreme levels of variability in Marbled Murrelet activity and our lack of understanding as to which factors drive that variability, it is critical that conclusions about activity or behavior not be drawn from data sets not specifically designed to answer the questions of interest.