O'Donnell and others 



Chapter 1 1 



Patterns of Seasonal Variation of Activity 



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LOST MAN CREEK 



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MAR MAY JUL SEP NOV JAN 



APR JUN AU6 OCT DEC FEB 



ONE-THIRD MONTH PERIODS 



Figure 1 Mean numbers of detections of Marbled Murrelets per survey (s.e.) for one-third- 

 month periods at three sites in northwestern California, 1989-1991 . Data from all years was 

 combined for calculations. Asterisks (*) denotes periods in which no birds were detected during 

 surveys; bars without standard error (vertical line segments) indicates only one survey was 

 conducted during the period; all other blank columns represent weeks in which no data was 

 collected. From O'Donnell 1993. 



(1988, 1990) felt the summer peak was likely the result of 

 increased activity by breeding birds in the stand, perhaps in 

 association with the fledging period, as opposed to an influx 

 of non-breeding birds. However, many investigators have found 

 that it is common among long-lived seabirds that defer sexual 

 maturity for immatures to visit breeding sites later in the 

 season in years prior to their first breeding attempt (Lack 

 1968, Sealy 1976, Gaston 1990). Sealy (1976) found increasing 

 numbers of subadult Ancient Murrelets (Synthliboramphus 

 antiquus) visiting nesting colonies later in the breeding season. 

 He found that attendance by subadults peaked by about one 

 month after 90 percent of adults and newly-hatched young 



had departed to sea. Increased activity at breeding stands in 

 July by Marbled Murrelets may indeed involve non-breeders 

 investigating potential breeding sites. An increased presence 

 by non-breeding birds later in the breeding season might also 

 contribute to the increase in flock size noted by both O'Donnell 

 (1993) and Rodway and others (1993b). 



In California, regular visitation at forest stands outside 

 of the breeding season has been established. Fall and winter 

 attendance has also been documented at several alcid colonies 

 (e.g., Common Murre, Uria aalge, Razorbill, Alca torda, 

 Black Guillemot, Cepphus grylle, Atlantic Puffin, Fratercula 

 arctica, and Cassin's Auklet, Ptychoramphus aleuticus), 



124 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



