Hamer and Nelson 



Chapter 4 



Nesting Chronology 



recorded on video tape fledging from a nest on 27 August 

 1990 (Hamer, pers. obs.). 



In British Columbia, incubation was estimated to 

 commence on 2 May and ended by 4 July (fig. 3). The nestling 

 period began 1 June and ended by 30 August. The total breeding 

 season was approximately 1 18 days. The earliest fledging date 

 recorded was for a juvenile collected by Drent and Guiguet 

 (1961) on 28 June 1961. The next five earliest records are of 

 all juveniles observed or collected at sea. The first grounded 

 fledging was not recorded until 7 July 1987 (Rodway and 

 others 1992). The latest two fledging dates occurred on 30 

 August. One was of a chick that was discovered after a tree 

 was felled (Harris 1971), and the second was a description of 

 the follicle development of a female (Sealy 1974). 



The length of the Alaska nesting season was greatly 

 restricted and was estimated to be only 106 days. Incubation 

 was estimated to begin on 14 May and end by 30 July. The 

 nestling period ranged from 13 June to 27 August. The 

 earliest fledging record was a juvenile observed at sea on 10 

 July 1 993. The next earliest was a grounded fledging observed 

 on 18 July 1987 (Mendenhall 1992). The latest estimated 

 fledging date of 27 August 1978 was from an active ground- 

 nest observed by Simons (1980). 



Sealy (1974) discovered that murrelets laid eggs in 

 British Columbia over a 6- to 7-week period beginning 15 

 May and ending in late June or early July. Adults with fish in 

 their bills were first observed on 16 June. Young birds were 

 first observed on the water on 6 July 1970 and on 7 July 

 1971. Sealy concluded that the period of egg laying and 

 incubation began around 15 May and lasted until 31 July. He 

 estimated that the period of hatching and chick rearing started 

 15 June and ended around 15 August. Fledging began in the 

 first week of July and continued to some time after 15 

 August (Sealy 1974). Sealy 's study took place in the most 

 northern portion of coastal British Columbia and thus may 

 be more representative of Alaska than British Columbia. His 

 breeding dates closely resemble the breeding chronology we 

 report for Alaska (fig. 3). Rodway and others (1992) reached 

 similar conclusions. 



For North America, Carter and Sealy (1987b) calculated 

 that egg-laying dates began between 15 and 22 April. The 

 latest fledging dates reported were 8 and 9 September. 

 Additional breeding records that we collected extend these 

 dates by several weeks in California and Oregon. However, 

 observations by Carter and Sealy of adults holding fish at 

 sea as late as 17 September and records of several young still 

 in downy plumage on 4 and 13 September led them to 

 believe that the nestling period of the murrelet may extend 

 into late September. Carter and Sealy concluded that murrelets 

 may nest earlier and have a longer breeding season south of 

 British Columbia. Carter (1984) speculated that the breeding 

 season was protracted in southern British Columbia as 

 compared to northern British Columbia. 



Carter and Erickson (1992) estimated that egg-laying 

 dates ranged from 15 April to 12 July in California, and 

 hatching from 15 May to 10 August. New records that we 

 examined extend these dates (fig. 3). Carter and Erickson 



found that fledging dates fell into two periods, 1 2 June to 4 

 July, and 1 1 August to 9 September. They believed the two 

 different fledging periods in California were due either to 

 low sample size, unknown factors affecting the grounding of 

 fledglings, or variation between years in the timing of 

 breeding. They concluded that egg laying begins earlier in 

 California than farther north. An earlier breeding chronology 

 was further supported by an examination of 45 museum 

 specimens which showed an earlier timing of prealternate 

 body molt for birds in California. 



Juvenile/Adult Ratios 



Adults molting into winter plumage can make it difficult 

 to discriminate between adults and juveniles after 15 August 

 (Carter and Stein, this volume). Because of this, for all 

 provinces and states combined, 29 percent of the juvenile 

 population produced in a given year may go uncounted if 

 surveys after 15 August cannot accurately census young 

 birds (fig. 2). It is impossible, at this time, with the small 

 sample sizes to calculate the percent of young expected to be 

 counted at sea during the breeding season for each state or 

 province. When collected, this information would be valuable 

 to researchers attempting to calculate juvenile/adult ratios or 

 model population trends. A full census of juveniles would 

 not be possible until after 16 September for California and 

 Oregon, and after late August in Washington, British 

 Columbia, and California. Sealy (1974) collected an adult 

 female in British Columbia on 9 July 1971 that had already 

 undergone a nearly complete body molt and was nearly in 

 winter plumage. He suggested that this female may have 

 undergone a premature body molt after an unsuccessful 

 breeding effort. A complete census of juveniles may not be 

 necessary for year-to-year comparisons of reproductive 

 success. But, if complete censusing is not done, researchers 

 should be careful of variations in the timing of breeding 

 between years when conducting any annual comparisons. In 

 addition, ratios of juveniles to adults observed at sea can be 

 adjusted for birds that have not yet fledged (Beissinger, this 

 volume) which may aid population modelling efforts and 

 annual comparisons of reproductive success. 



Acknowledgments 



We are grateful for the unpublished accounts of nest 

 observations, grounded chicks, and grounded fledglings 

 provided to us by Nancy Naslund of the U.S. Fish and 

 Wildlife Service, U.S. Department of Interior, Steve Singer 

 of the Santa Cruz Mountains Murrelet Group, Bill Ritchie of 

 the Washington Department of Wildlife, Paul Jones, Phyllis 

 Reed, and Brenda Craig of the USDA Forest Service. Ray 

 Miller and Sal Chinnici of the Pacific Lumber Company 

 provided information from a nest in northern California. We 

 thank Craig Strong, C.J. Ralph, Kathy Kuletz, and Susan 

 Speckman for providing records of juveniles first observed 

 at sea during marine survey efforts. Joanna Burger, Anthony 

 Gaston, and Frank Pitelka provided helpful comments on 

 early drafts of this manuscript. 



56 



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



