Chapter 24 



Monospecific and Mixed Species Foraging Associations of 

 Marbled Murrelets 





George L. Hunt, Jr. 1 



Abstract: Marbled Murrelets (Brachyramphus marmoratus) vary 

 in the frequency with which they are associated with mixed species 

 foraging flocks of seabirds. When foraging in the exposed waters 

 of the outer coasts, murrelets are almost invariably found in pairs 

 or small monospecific flocks. In protected waters, they are fre- 

 quently associated with other species. The reasons for these differ- 

 ences are unknown. An increase in the number of gulls foraging in 

 association with murrelets could be detrimental to the murrelets if 

 it resulted in an increased rate of kleptoparasitism. 



Marbled Murrelets (Brachyramphus marmoratus) 

 occupy a variety of foraging habitats and vary in their 

 propensity to forage in the company of other seabirds. In 

 this brief review, I contrast two types of habitats used by 

 foraging murrelets, and discuss the likelihood that murrelets 

 will be accompanied by foragers of other seabird species. 

 Because marbled murrelets may be subject to kleptoparasitism 

 in these mixed species flocks, it is possible that changes in 

 the relative abundance of the species in these flocks could 

 impact the foraging success and ability of murrelets to 

 provision young. 



Habitats Used 



Marbled Murrelets occur in nearshore (usually less than 

 2 km from shore) waters from central California to Alaska. 

 Within this range, murrelets are found in two different 

 habitats: along the open "outer" coasts, and in the protected 

 inshore waters of bays, sounds, and inlets. In California, 

 Oregon, the outer coast of Washington, and parts of the 

 west coast of Vancouver Island, murrelets use coastal waters 

 at the edge of the open ocean. These coasts are occasionally 

 intersected by rivers with their associated offshore plumes, 

 or headlands that may set up eddies or fronts in their vicinity. 

 However, for the most part, these waters are lacking in 

 obvious features that should result in predictable, small- 

 scale concentrations of prey. In contrast, in the more protected 

 bays, sounds and inlets of British Columbia, Alaska, and 

 Puget Sound, there are often strong tidal currents that interact 

 with bathymetric features to create eddies, rips and others 

 features where prey predictably concentrate. In addition, 

 these waters are often nursery areas for young schooling 

 fish that forage in quiet bays as well as in association with 

 tidal features such as rips and eddies. 



1 Professor, Department of Ecology and Evolutionary Biology, Univer- 

 sity of California, Irvine, CA 92717 



Foraging Associations 



The foraging behavior of Marbled Murrelets, particularly 

 the propensity to be associated with mixed species foraging 

 flocks, appears to differ between exposed and sheltered waters. 

 Although quantitative data are lacking, murrelets are usually 

 found in pairs, or occasionally in small monospecific flocks 

 along the exposed ocean coast (Ainley and others, this volume; 

 Strachan and others, this volume); I observed this to be also 

 true of the Xantus' Murrelet (Synthliboramphus hypoleuca) 

 in the waters near the Channel Islands of the Southern 

 California Bight. It is not known why these two species of 

 birds prefer to forage as pairs in the open ocean. Xantus' 

 Murrelets specialize on young-of-the-year northern anchovies 

 (Engraulax mordans) (Hunt, unpublished data) and marbled 

 murrelets take these as well as other species of small, schooling 

 fish (Burkett, this volume). Cooperative foraging may be 

 more efficient when hunting for these fish, but many species 

 of seabirds forage as singletons when taking the same fish 

 species. In central California, murrelets were also occasionally 

 found in small (up to 25 individuals) flocks, with some of 

 these flocks being in the vicinity of river mouths (Ralph and 

 Miller, pers. comm). None was accompanied by other species 

 of seabirds. Likewise, near Barkley Sound on the west coast 

 of Vancouver Island, Porter and Sealy (1981) reported that 

 outside the sound, murrelets did not participate in any of 

 seven mixed species foraging flocks. Sealy (1973b) found 

 marbled murrelets in about 4 percent of mixed species flocks 

 off Langara Island, British Columbia, but most birds along 

 the outside of the west coasts of Vancouver Island and the 

 Queen Charlotte Islands were thought to forage singly or in 

 monospecific pairs (Carter 1984; Carter and Sealy 1990; 

 Sealy 1973b, 1975c). Chilton and Sealy (1987) suggested 

 that the low frequency of murrelet participation in mixed 

 species foraging flocks was a means of avoiding competition 

 with larger, more aggressive species of seabirds. 



Despite the potential for competition with other species 

 of seabirds and kleptoparasitism from gulls in protected 

 waters from Washington to Alaska, Marbled Murrelets 

 frequently forage in mixed species flocks (Piatt, pers. comm.; 

 Hunt, pers. obs.; Burger, pers. comm.). For example, in the 

 protected waters within Barkley Sound, Porter and Sealy 

 (1981) found murrelets present in 7 of 27 mixed species 

 feeding flocks. Recently, Mahon and others (1992) 

 documented the role of Marbled Murrelets in foraging flocks 

 in the protected inlets of the Strait of Georgia, British 

 Columbia. They found that the number of feeding flocks 

 observed in an area was positively correlated with the 

 number of murrelets present. They observed that in 100 of 



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



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