Strachan and others 



Chapter 23 



At-Sea and Foraging Behavior 



about the need for foraging in groups. McAllister (unpubl. 

 data) found in Alaska, between mid- July and mid-August, 

 that more than 80 percent of the young were observed without 

 adults present. By contrast, in California, Ralph and Long 

 (this volume) observed that half of the juveniles observed 

 were accompanied by one or more adults, while the remaining 

 juveniles occurred alone. 



By mid-August, it becomes difficult to differentiate 

 juvenal plumage from molting adults. In our observations of 

 juveniles on the water, we found that juveniles foraged 

 without the assistance of the adults. They were seen as single 

 birds, in pairs, and in small flocks. The largest flock was one 

 of 12 young seen together in Peril Strait (McAllister, unpubl. 

 data). Juveniles were most common within 100 m of 

 shorelines, particularly where bull kelp (Nereocystis spp.) is 

 present (McAllister, unpubl. data). At this time of year, 

 adults were generally farther from shore in this area, at the 

 sharp tidal interfaces, e.g. rips. However, in a 1993 study, 

 Ralph and Long (this volume) found no difference between 

 the distribution of adults versus juveniles in California. 



Behaviorally, the fledglings are generally less wary, 

 more curious, and much more approachable by boat. In 

 flight, they are weak and slow (McAllister, unpubl. data), as 

 compared to adults. 



Interspecific Relations During Foraging 



In the southern part of the range, from Washington 

 south, murrelets rarely forage in mixed seabird flocks. Pairs 

 or small flocks will usually forage away from other species. 

 In California and Oregon, murrelets have been reported 

 foraging close to Pigeon Guillemots (Cepphus columba) and 

 Common Murres (Uria aalge), but seldom within any major 

 mixed species flocks. Murrelets have been observed by Strong 

 and others (1993) to avoid large feeding flocks of murres, 

 cormorants (Phalacrocorax spp.), and other species in Oregon. 

 He presumed that the small size of the murrelet may render 

 them vulnerable to kleptoparasitism or predation in mixed 

 species flocks. In addition, if the murrelets forage in some 

 cooperative effort, the confusion of a large flock of birds 

 might reduce foraging efficiency. 



In the northern part of the range of the murrelet, from 

 Puget Sound north, the literature has more records of the 

 bird mixing with other seabirds when foraging (e.g., Hunt, 

 this volume b). In this region, Marbled Murrelets were less 

 common than the other species in the flocks, and rarely 

 initiated the feeding flock (Porter and Sealy 1981; Chilton 

 and Sealy 1987). Porter and Sealy (1981) found in Barkley 

 Sound, British Columbia, that the murrelet had the lowest 

 flocking tendency (0.2 percent) of the birds seen participating 

 in multispecies feeding flocks, although there they did 

 appear to initiate feeding flocks. Mahon and others (1992) 

 observed that murrelets participate frequently in mixed 

 species feeding flocks in the Strait of Georgia, British 

 Columbia. They found a correlation between the number 

 of feeding flocks observed in the area and the number of 

 murrelets present. Chilton and Sealy (1987) suspected that 



murrelets enter small flocks to minimize disturbance from 

 larger, more numerous, and aggressive individuals of other 

 species that would find single birds easy to intimidate. 

 Mixed flocks would occur after murrelets drove a school 

 of sand lance to the surface. Other species participating in 

 these feeding flocks in order of relative occurrence were 

 Glaucous-winged Gulls (Larus glaucescens), Bonaparte's 

 Gulls (Larus Philadelphia), Common Mergansers (Mergus 

 merganser). Pigeon Guillemots, Mew Gulls (Larus canus), 

 and Pelagic Cormorants (Phalacrocorax pelagicus). They 

 felt that several factors encouraged a higher level of 

 interspecific flocking behavior by murrelets: (1) larger 

 and more aggressive alcids, such as Common Murres 

 were absent; (2) the area had a high density of Marbled 

 Murrelets; and (3) prey were locally concentrated, as the 

 fish balled up at the surface when attacked, likely facilitating 

 flock formation. 



In Alaska, the foraging flock of 4,000-6,000 Marbled 

 Murrelets on 3 May 1991 in Icy Strait contained an equal 

 number of Bonaparte's Gulls (McAllister, unpubl. data). 

 Both species were feeding actively on what was suspected to 

 be the hatch from a recent herring spawn. In southeast Alaska, 

 McAllister (unpubl. data) found that Marbled Murrelets were 

 rare in the areas where Common Murres and Rhinoceros 

 Auklets (Cerorhinca monocerata) from the Forrester Island 

 colony foraged around Prince of Wales Island. This area 

 contains much suitable nesting habitat for murrelets, including 

 large, contiguous stands of old-growth trees, but murrelets 

 apparently avoid the region. He has also observed this at 

 colonies near Saint Lazaria Island, in Sitka Sound, and Hazy 

 Islands group. 



In the Gulf of Alaska, where the range of the Kittlitz's 

 Murrelet (Brachyramphus brevirostris) overlaps with that of 

 the Marbled Murrelet, the two species often share common 

 foraging areas (McAllister, unpubl. data). However, the two 

 species were not found to interact as pairs or in flocks. 



Diving 



Marbled Murrelet foraging is by pursuit diving (Ashmole 

 1971). Depth and time of murrelet dives are little known. 



Dive times We have recorded dive times of birds using 

 birds with transmitters that were monitored by an observer 

 on shore. When birds are underwater, the transmitter can no 

 longer be heard. We also present some data from birds 

 observed from shore through telescopes. 



Dive times were obtained from six birds fitted with 

 transmitters in studies in 1989 and 1991 in northern 

 California. The birds were followed on 13 occasions by a 

 monitor on shore. The median dive times averaged 14 

 seconds, with the longest at 69 seconds. The mean length of 

 pauses between dives averaged 17 seconds in each year. 

 Rest times were naturally more variable, with as long as 18 

 minutes between dives. 



From-shore observations at Ano Nuevo Bay in California, 

 birds were observed with dive times ranging from 7 to 42 

 seconds. The depth of water for the 7-second dive was 1 -2 



250 



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



