Ralph and Long 



Chapter 35 



Productivity in California-Observations At Sea 



basic-like plumage that we aged by missing primaries or 

 molting areas on the belly, neither of which would be seen 

 unless the bird flapped its wings. A substantial number of 

 adults were classified as birds of unknown age during this 

 period. Obviously, most of these were actually adults. By 19 

 September, 90 percent of the population was in basic or 

 near-basic plumage. 



Discussion 



Our results, using more rigorous methods than previously 

 employed, confirmed productivity estimates from California 

 over the previous five years of under 3 percent. Such a low 

 productivity may indicate a population with a very low 

 reproductive rate. However, we may also be missing some of 

 the juveniles in our surveys if they are distributed differently 

 on the ocean than the adults. In our experience, single birds 

 are usually more difficult to detect from boats. Varoujean 

 (pers. comm.) found during aerial surveys that many juveniles 

 were alone. In British Columbia, Sealy (1974) found about 

 64 percent of juveniles were seen alone, 20 percent were seen 

 with adults, 14 percent were with another juvenile, and 4 

 percent were in a group of three or more juveniles. We also 

 found as many juveniles alone as in groups, similar to that 

 found by Sealy, though none were with other known juveniles 

 as in his study. Therefore, we may have missed single juveniles. 



There may also be a difference in habitat use by each 

 age group. There is evidence that murrelets as well as other 

 seabirds tend to be distributed in clumps at sea (Harrison 

 1982, Sealy 1973b). Strong and others (1993) found adult 

 murrelets tended to switch foraging areas between July and 

 August, perhaps in response to prey resources. They also 

 found a patchy distribution of juveniles, with concentrations 

 in three areas on the Oregon coast, which may have been 

 similar to the distribution of adults. 



Another aspect of habitat selection is distance from 

 shore. Sealy (1975a) and McAllister (pers. comm.) both 

 found juveniles congregated in nearshore kelp beds in British 

 Columbia and Alaska, while more adults were offshore. 

 Kaiser and others (1991) in Malaspina Inlet and Desolation 

 Sound, British Columbia also found a similar distribution 

 between the young and adults in early August. If there is a 

 difference in distribution between ages in respect to distance 

 from shore, then the use of telescopes from land for 

 determining age ratios may skew the data towards more 

 juveniles. In our study, we did find 35 percent of the juveniles 

 seen from boats were within 400 m of the coast where they 

 would be easily seen from shore (table 3). However, we 

 found no difference in the distribution of juveniles versus 

 adults relative to distance from shore, so this would not 

 likely skew the results, at least in our data. More research on 

 the behavioral differences of adults versus juveniles will be 

 an integral part of estimating murrelet productivity. 



The highest percentages of juveniles were found in the 

 earliest periods of the study in June and July (6 percent). 

 This estimate may be the most accurate, as compared to late 



August, since juveniles were difficult to identify when some 

 adults were well into the molt (Carter and Stein, this volume). 

 By early August, about 75 percent of the birds have probably 

 fledged (Hamer and Nelson, this volume a). Unless the 

 primaries were seen, many black-and-white birds were 

 classified as unknown. Thus, the decline in the percent of 

 juveniles in late August may reflect this. The slight increase 

 in juveniles in early September may be a result of the small 

 sample, or indicate a second breeding attempt, as suggested 

 by Hamer and Nelson (this volume a). 



We found that some adults on the California coast started 

 molt at least as early as 21 June (fig. 1), and by mid- August, 

 three-fourths of the adults were in molt. This is earlier than 

 previously reported (e.g., 20 July in British Columbia [Sealy 

 1975a]). If it takes about 2-3 months for the entire molt to be 

 completed (see Carter and Stein, this volume), these birds 

 might have been in basic plumage by late August. Indeed, 

 about 10 percent of the sample of adults had a substantial 

 basic plumage in the 20-29 August period (fig. 2). The 

 remainder of the adults still retained much of their breeding 

 plumage and were distinguishable from juveniles. Therefore, 

 it appears that August 15 is a conservative date for considering 

 a black-and-white plumaged bird as a juvenile. We are thus 

 relatively confident that our identification prior to this date is 

 accurate. This date will lead to some underestimate of juveniles, 

 since approximately 15 percent of the juveniles have not 

 fledged until after mid- August (Hamer and Nelson, this volume 

 a). By late August, this has decreased to less than 5 percent. 



These estimates of production, however, do not take 

 into account the numbers of non-breeders in the population. 

 Since there are no good estimates of proportions of non- 

 breeders for this bird, we must look to other species. Other 

 small alcids do not breed until about 3 years of age. Examples 

 are Ancient Murrelets (Synthliboramphus antiquus), and 

 Crested (Aethia cristatella), Least (Aethia pusilld), and 

 Cassin's (Ptychoramphus aleuticus) auklets (De Santo and 

 Nelson, this volume; Gaston 1992) which live about 5-10 

 years. Thus, if we assume that they breed at 3 years, and the 

 average life span is 7.5 years, then 2 years out of an average 

 of 6.5 years (or 2/6.5 = 30.7 percent) of an adult's life are 

 spent as a non-breeder. So, almost one-third of the 1,061 

 adults in our sample, or 326 birds, may not be breeding, 

 leaving only 735 breeders sampled. Also, we may assume 

 that early in the season when the first fledglings are coming 

 off the nest, a breeding pair that is still feeding young may 

 sometimes not be on the water at the same time, therefore 

 only one of a breeding pair is counted. If we make a 

 conservative estimate that a fourth of the birds seen on the 

 water represent one member of a nesting pair, we would add 

 another 185 birds for a total of 920 potential adult breeding 

 adults, or 460 pairs, of the 1,061 adults. Consequently, a 

 revised estimate of production would be 26 chicks/460 pairs 

 or 5.0 percent, which is still quite low. 



There is a difference in the method of evaluation of 

 plumages between our field study and Carter and Stein's 

 (this volume) analysis of study skins. In their method, they 



376 



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



