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1 July 2000 MEASURING MARBLED MURRELET ACTIVITY IN VALLEY BOTTOM HABITAT: BIAS DUE TO STATION PLACEMENT
Michael S. Rodway, Heidi M. Regehr
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Abstract

Survey stations to measure Marbled Murrelet (Brachyramphus marmoratus) activity in low-elevation forest are often preferentially placed on stream channels because they provide wide visibility and the greatest chances of visually detecting birds and thus behaviors possibly associated with nesting. Detections of birds flying along stream channels to access nesting habitat farther inland will inflate estimates of activity associated with the adjacent forest. We compared numbers and types of murrelet detections between 12 paired stations within 100 m of each other on streambeds and in similar habitat in adjacent forest during 8 Jun–10 Jul. 1997 in Clayoquot Sound, British Columbia. Circling and below-canopy flight, thought to be indicative of nesting, were observed at all streambed survey stations and at less than half of paired forest stations. Numbers of such “occupied” detections were six times greater at streambed than forest sites. Size of opening at survey stations accounted for much of the difference in detection rates between forest and streambed stations, but numbers of total, visual, and occupied detections, specifically those of circling birds, were lower at forest than streambed stations even after the effect of opening size had been considered. Correlations between opening size and numbers of detections at streambed but not at forest locations, also indicated that differences between streambed and forest stations were not solely a function of opening size. Observations at one pair of stations where murrelets were using a flight corridor over the forest station indicated that a corridor effect may not be confined to streambed locations. Results indicated that placement of survey stations on stream channels is appropriate if the goal is to determine murrelet presence or the occurrence of occupied detections in an area. However, if a comparison of murrelet activity between habitat types is the objective, then forest stations with comparable opening sizes may be needed to provide unbiased results.

Michael S. Rodway and Heidi M. Regehr "MEASURING MARBLED MURRELET ACTIVITY IN VALLEY BOTTOM HABITAT: BIAS DUE TO STATION PLACEMENT," Journal of Field Ornithology 71(3), 415-422, (1 July 2000). https://doi.org/10.1648/0273-8570-71.3.415
Received: 27 July 1998; Accepted: 1 March 1999; Published: 1 July 2000
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