Patterns of activity and vocalizations of the marbled murrelet, Brachyramphus marmoratus, within old-growth redwood stands in northwestern California

Patterns of activity and vocalizations of marbled murrelets were studied in coastal old-growth redwood stands in northwestern California, from Spring, 1989 through the Summer, 1991. Morning surveys for murrelets were conducted at nine sites through the summer of 1989. Thereafter, due to logistical constraints, only three of the nine sites were monitored through August 1990, and then surveys were continued at two sites for the remainder of the study period. Data for each detection of a murrelet(s) were recorded on cassette tape, and included: estimated number of murrelets heard or seen during each detection; number and type of calls; compass direction at which a murrelet(s) was first detected; closest distance the murrelet(s) came to the observer; behavior of murrelet(s); and the compass bearing on which the murrelet(s) departed. I examined seasonal changes in murrelet activity and vocalizations. Activities were also compared between years and between sites. Numbers of detections of murrelets did not differ between years in any given month. Above and below canopy activity was similar between years and differed in only a few months. There were no consistent patterns of greater or lesser numbers of detections or above and below canopy activity in any year. Murrelets visited the stands in both the breeding and non-breeding seasons, and exhibited consistent, seasonal patterns of activity and vocalizations at the different sites. Detections of birds was greatest during the breeding season, falling to lesser levels during the non-breeding season, and reaching few or no detections during fall and spring molts. Murrelets were observed flying into and below the canopy almost exclusively during the breeding season. Flocks observed above the canopy were larger than those observed below the canopy, and all flocks had fewer individuals in May and June. Murrelets flying above the canopy were much more vocal than those below the canopy, but no seasonality was observed in the occurrence of different vocalizations.