Hamer and Nelson 



Chapter 4 



Nesting Chronology 



cumulative percentage change in the total number of young 

 fledged from 20 May to 18 June was low, increasing only 1- 

 6 percent between each 10-day period. A gradual accumulation 

 of fledglings on the ocean would be predicted from 19 June 

 until 27 August. During this period the cumulative percent 

 change in the number of juveniles fledging between each 10- 

 day period was very consistent, ranging from 9 to 15 percent. 

 The latter part of the nesting season from 28 August to 26 

 September was similar to the beginning of the season, with 

 the cumulative percent change in the number of young fledged 

 ranging from 1 to 5 percent. For all states and provinces 

 combined, the results show that by 27 August, only 84 

 percent of the juveniles in a given year would be expected to 

 be counted at sea using marine census techniques. For 

 California and Oregon, a census of all juveniles would not 

 occur until the third week of September (fig. 3). In Washington, 

 British Columbia, and Alaska, a full census of all juveniles 

 would not occur until the third week of August (fig. 3). 



Discussion 



The breeding season of the Marbled Murrelet appears to 

 be much longer than that of many other members of the alcid 

 family. The long breeding period indicates that the 



synchronous nesting exhibited by many colonial and semi- 

 colonial nesting seabirds is likely not a characteristic of the 

 breeding biology of the Marbled Murrelet. Few active nests 

 have been found within the same stand to verify this. In one 

 instance, two active nests were found only 100 m apart in the 

 same forest stand in Washington. The first nest fledged a 

 young murrelet on 18 July with the second nest fledging on 

 27 August, a 39-day difference (Hamer, pers. obs.). A trend 

 toward a shorter breeding season in the northern range of the 

 murrelet is apparent as one examines the fledging dates from 

 California to Alaska (table 2, fig. 3). The longest breeding 

 period was observed in California. Oregon had the next 

 longest breeding period. The breeding season in Alaska was 

 64 days shorter than California. 



For California and Oregon, a larger sample of breeding 

 records is needed to further refine the breeding period and 

 conduct statistical tests to determine whether two distinct 

 breeding seasons exist. The fact that each breeding period 

 was similar in total length supports the idea that there are 

 two periods. When examined separately, the second breeding 

 period was only 1 2 and 1 6 days shorter than the first breeding 

 period for Oregon and California, respectively. The first 

 breeding period in California (103 days) was similar to the 

 total breeding season in Alaska (106 days). 



Mar Apr May Jun Jul Aug Sep 

 1 15 31 15 30 15 31 15 30 15 31 15 31 15 



Incubation 



ALASKA 

 n=12 



BRITISH COLUMBIA 

 n=23 



WASHINGTON 

 n=13 



OREGON 

 n=13 



Nestling 



Incubation 



Nestling 



Incubation 

 H 



Nestling 



Incubation 



Nestling 



Incubation 



CALIFORNIA 

 n=25 



Nestling 



1 15 31 15 30 15 31 15 30 15 31 15 31 15 

 Mar Apr May Jun Jul Aug Sep 



Figure 3 Breeding phenology of the Marbled Murrelet in North America organized by state and 

 province. The median for each incubation and nestling period is shown. 



54 



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



