Treesearch

Information on food habits of the Marbled Murrelet (Brachyramphus marmoratus) was compiled from systematic studies and anecdotal reports from Alaska to California. Major differences between the winter and summer diets were apparent, with euphausiids and mysids becoming more dominant during winter and spring. The primary invertebrate prey items were euphausiids, mysids, and amphipods. Small schooling fishes included sand lance, anchovy, herring, osmerids, and seaperch. The fish portion of the diet was most important in the summer and coincided with the nestling and fledgling period....

Marbled Murrelets (Brachyramphus marmoratus) occupy nearshore waters in the eastern North Pacific Ocean from central California to the Aleutian Islands. The offshore marine ecology of these waters is dominated by a series of currents roughly parallel to the coast that determine marine productivity of shelf waters by influencing the rate of nutrient flux to the euphotic zone. Immediately adjacent to the exposed outer coasts, wind driven Ekman transport and upwelling in the vicinity of promontories and other features create zones of enhanced primary production in which primary and secondary...

Mortality of Marbled Murrelets (Brachyramphus marmoratus) due to oil pollution is one of the major threats to murrelet populations. Mortality from large spills and chronic oil pollution has been occurring for several decades but has been documented poorly throughout their range; it probably has contributed to declines in populations, in conjunction with loss of nesting habitat and mortality in gill nets. The 1989 Exxon Valdez oil spill in Alaska caused the largest single mortality of murrelets (about 8,400 birds) in the world and contributed to decline in murrelet populations in Prince...

We examined the range and the relationships of Marbled Murrelet (Brachyramphus marmoratus) behavior with habitat and landscape characteristics in isolated old-growth and residual forest stands from 2 to 400 ha in California. In large contiguous stands of old-growth forest in parks, we examined relationships of murrelet detections with elevation and topography. In isolated stands we found higher murrelet detection levels in stands with higher dominant and codominant crown cover and >50 percent coast redwood (Sequoia sempervirens). Surveys also were more likely to detect occupied behaviors...

The principal pollutant threats to Marbled Murrelets are chlorinated organic effluent discharges from chlorine bleach pulp mills located in California, Washington, and British Columbia. The distribution of murrelets away from riverine input of agricultural chemicals reduces the threat from these pollutants. Plastic ingestion does not appear to pose a serious threat to murrelets, as it does for other species of small alcids. Significant threats from oil pollution are present because of heavy oil tanker, commercial shipping, and barge traffic along the Pacific coast. Commercial fishing...

Marbled Murrelets have distinct basic, alternate and juvenal plumages. In after-hatching-year (adult) birds, the incomplete pre-alternate molt occurs rapidly over a period of about one month per individual between late February and mid-May. The complete pre-basic molt occurs between mid-July and December. At this time, individuals are flightless for about two months. In late summer, it is difficult to distinguish adult birds undergoing prebasic molt from juveniles at sea. Field methods for separating these age categories at sea at this time of the year are presented. By early fall, older...

Little research has been done to quantify and describe the structural characteristics of forest stands that are associated with Marbled Murrelet (Brachyramphus marmoratus) nesting in the Pacific Northwest. Vegetation measurements and murrelet surveys to determine occupancy were conducted in stands located throughout western Washington. I used logistic regression to contrast stand attributes between occupied (n = 64) and unoccupied (n = 87) stands. The probability of occupancy of an old-growth stand increased with increasing total number of potential nest platforms, percent moss coverage on...

The behavior of Marbled Murrelets (Brachyramphus marmoratus) at sea while foraging for small fish and invertebrates is poorly known. This murrelet forages by pursuit diving in relatively shallow waters, usually between 20 and 80 meters in depth. We have also observed it diving in waters less than 1 meter and more than 100 meters deep. The majority of birds are found as pairs or as singles in a band about 300 to 2000 meters from shore. Pairs tend to dive simultaneously when foraging, and we suggest that pairing has some benefit to foraging efficiency. At times they are in small flocks and...

Relationships between landscape-level patterns of forest cover and occupancy by Marbled Murrelets in the state of Washington where state-wide forest-cover information was available were investigated. Using a geographic information system, a 203-hectare circular area surrounding each of 261 previously surveyed locations was delineated. Within each area, we calculated the amount, distribution, and pattern of various classes of late-seral forest. Proportions of old-growth forest and large sawtimber were greater at sites that were occupied by murrelets than at sites where they were not...

Marbled Murrelets (Brachyramphus marmoratus) vary in the frequency with which they are associated with mixed species foraging flocks of seabirds. When foraging in the exposed waters of the outer coasts, murrelets are almost invariably found in pairs or small monospecific flocks. In protected waters, they are frequently associated with other species. The reasons for these differences are unknown. An increase in the number of gulls foraging in association with murrelets could be detrimental to the murrelets if it resulted in an increased rate of kleptoparasitism.