Chapter 4 



Nesting Chronology Of The Marbled Murrelet 



Thomas E. Hamer 1 



S. Kim Nelson 2 



Abstract: We compiled 86 breeding records of eggs, downy young, 

 and fledgling Marbled Murrelets (Brochyromphus marmorotus) 

 for which the fledging date could be estimated. Records were 

 collected from California (n = 25), Oregon (n = 13), Washington 

 (n = 13), British Columbia (n = 23), and Alaska (n = 12). The 

 number of young fledging increased rapidly from 6 June to 19 July 

 and peaked by the 10-day period beginning 19 July. A second peak 

 in the number of young fledged was observed for the 1 0-day period 

 beginning 18 August, with a rapid decrease in late August and 

 early September. From these results, a gradual accumulation of 

 fledglings on the ocean would be observed from 30 May until 16 

 September. By 27 August, only 84 percent of the juveniles in a 

 given year would be expected to be counted at sea. In California 

 and Oregon, it is likely that two distinct periods of breeding 

 activity result from some proportion attempting to lay a second 

 clutch, or pairs renesting after nesting failure. The breeding season 

 appears to be much longer and less synchronous than that of many 

 other members of the alcid family. We conclude that egg-laying 

 and incubation spanned a long period, beginning 24 March and 

 ending 25 August, with the nestling period beginning 23 April and 

 ending with a fledging record on 21 September, a breeding period 

 of 182 days. 



Detailed information on the breeding chronology of the 

 Marbled Murrelet (Brachyramphus marnwratus) has been 

 limited. More recently, a large amount of unpublished 

 information has been collected from research projects being 

 conducted throughout the range of the Marbled Murrelet. In 

 this paper we review the nesting chronology of the Marbled 

 Murrelet using data from four published studies that 

 specifically addressed the topic (n = 26 records), additional 

 published breeding records (n = 26), and unpublished breeding 

 accounts (n = 35) of the Marbled Murrelet from Alaska, 

 British Columbia. Washington, Oregon, and California. This 

 information was used to estimate the fledging dates for each 

 record collected. We then summarized these fledging dates 

 and used them to construct the timing of egg laying, 

 incubation, and nestling period for each state and province 

 to more accurately document the breeding chronology of 

 the Marbled Murrelet. 



An understanding of the breeding chronology of the 

 Marbled Murrelet is important for several reasons. To learn 

 more about the nesting ecology of this species, it is important 

 to understand the timing and lengths of breeding activities 

 and what factors affect this timing. To avoid disturbance to 

 nesting colonies from land management activities, land 



1 Research Biologist, Hamer Environmental, 2001 Highway 9, Mu 

 Vemon, WA 98273 



: Research Wildlife Biologist, Oregon Cooperative Wildlife Research 

 Unit, Oregon State University, Nash 104, Corvallis, OR 97331-3803 



managers will need to know the timing of the incubation and 

 nestling periods for each geographic area. Biologists 

 conducting nest searches and gathering information on nesting 

 biology will want to know the optimum period to conduct 

 these activities. In addition, biologists conducting marine 

 surveys to collect information on the numbers of juveniles 

 observed at sea, as an indication of reproductive success, 

 will need nesting chronology data to determine the appropriate 

 timing of these surveys. 



Several studies have addressed the breeding chronology 

 of the Marbled Murrelet. In British Columbia, Sealy (1974) 

 collected female specimens at sea and examined the 

 maturation of the ovarian follicles, the size of the brood 

 patch, and the date juveniles were first observed on the 

 ocean. Carter and Sealy (1987b) used 41 records of downy 

 young and grounded fledglings to estimate the timing of 

 breeding. Carter and Erickson (1992) used additional records 

 of grounded chicks and fledglings to estimate the timing of 

 egg laying, incubation, and chick rearing for murrelets in 

 California. In addition, the breeding phenology of the murrelet 

 in British Columbia was reviewed by Rodway and others 

 (1992), adding some records to the previous work of Sealy 

 (1974) and Carter and Sealy (1987b). 



Methods 



We compiled unpublished breeding records from 

 intensive field work conducted on murrelets over the last 

 five years, and from published observations of breeding 

 records, downy young and fledgling Marbled Murrelets (table 

 1). Fledging dates were estimated using a 30-day incubation 

 period and a 28-day nestling period (Sealy 1974, Simons 

 1980, Hirsch and others 1981). For example, if a grounded 

 chick was found and, from the description, was estimated to 

 be 10 days old, we added 18 days to determine the approximate 

 fledging date. Similarly, if an egg-laying date was available, 

 but the egg was destroyed before hatching, we added 30 

 days for incubation and a 28-day nestling period to estimate 

 the fledging date. The initiation of egg laying, incubation, 

 and hatching were estimated for each record in the same 

 manner. In some cases, where the size and plumage of a 

 chick were not described completely, a subjective estimate 

 of the age of the chick was made. These records were given a 

 higher error estimate. Fledging dates were used for the analysis 

 only if the date could be estimated with an error of <8 days 

 so that the results would accurately describe the nesting 

 chronology. Records were not used when a description of 

 the plumage or size of the chick was not available. Records 

 derived from juveniles first observed at sea were used only if 

 the researcher was conducting weekly boat surveys within 



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



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