Strachan and others 



Chapter 23 



At-Sea and Foraging Behavior 



night. Certainly murrelets must be able to locate prey species 

 where or when there is little ambient light. 



Many observations of fish holding occur at dusk. At 

 nests, observations of nestlings being fed whole fish have 

 almost always been during first light at dawn (Nelson and 

 Hamer, this volume a). Foraging for nestlings therefore 

 would probably occur during the early morning periods 

 when there is enough light for the murrelets to catch prey. 

 We feel that observations of adults holding fish are strong 

 indicators of a bird about to depart inland to feed a young. 

 As such, this may be a sensitive measure of birds with 

 young on the nest, potentially a very useful measure of 

 reproductive rate in this species. 



The majority of birds on the water are in pairs. We do 

 not know what proportion of these are mated birds, or what 

 proportion are birds temporarily paired for foraging. 

 Observations of murrelets in groups of more than four are 

 rarely foraging, and appear to be largely loafing. In most 

 cases, pairs on the water dive simultaneously, strongly 

 suggesting to us an apparent benefit to foraging. We can find 

 no evidence that pairs on the water during the breeding 

 season are actually mates involved in breeding. By the same 

 token, we do not know if single birds belong to a pair of 



incubating birds. We feel that it is likely that the species has 

 evolved a yet-undescribed feeding strategy that involves 

 cooperative herding of schools of small fish. 



Flock size appears to be related to the size of the regional 

 populations, prey availability, and possibly juvenile behavior. 

 The largest flocks are in areas with the largest populations of 

 birds. There are no obvious behaviors related to flocking, 

 other than loafing, that have been reported. 



We very much need more work in several areas relating 

 to offshore behavior. Since it is possible to completely 

 census birds on the water, and much of the adult mortality 

 probably takes place here, it is vital that we have a fuller 

 understanding of the factors involving the distribution, 

 abundance, feeding behavior, juvenile behavior and 

 survivorship, at-sea social behavior, as well as many other 

 factors, of these interesting birds. 



Acknowledgments 



We thank Alan Burger, George Hunt, Sherri Miller, 

 William Sydeman, and Craig Strong for many helpful 

 comments on this manuscript. We also thank Linda Long for 

 creating the figures. 



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



253 



