Ralph and others 



Chapter 1 



Overview of Ecology and Conservation 



Washington, Oregon, and California. The observations that 

 murrelets redistribute themselves after young have fledged 

 indicate that food may be more abundant or accessible 

 elsewhere. We thus conclude that the large-scale at-sea 

 distribution and abundance of murrelets during the breeding 

 season is not primarily related to the distribution and 

 abundance of prey. It is possible, however, that the amount 

 of prey offshore of old-growth influences the number of 

 murrelets that breed there. Additionally, prey abundance 

 may be influenced by oceanographic events that cause 

 widespread, as well as local, reduction of productivity and 

 prey availability. 



(b) Winter visitation of nesting sites Some murrelet 

 populations continue to visit breeding areas during the winter 

 (Naslund 1993), indicating that nest sites need to be defended 

 year round. This is a behavior seen in other alcids when 

 there is competition for nest sites (Ainley and Boekelheide 

 1990), and site retention may require sustained occupancy 

 through the winter. Winter visitation by murrelets, however, 

 was not apparent in British Columbia because the birds 

 leave offshore areas near nesting sites in many parts of the 

 Province (southwest Vancouver Island, and the Queen 

 Charlotte Islands) (Burger, this volume b). 



(c) Limitation of nest sites and habitat saturation 

 Spacing of nesting pairs might lead to unused nest sites in 

 some areas, but in others, high quality nest sites might be 

 relatively infrequent, even in old-growth forest (Naslund, 

 pers. comm.). The short stature of most Alaskan old-growth 

 and the forms of some old-growth tree species at lower 

 latitudes (for instance, redwoods have few large or deformed 

 limbs) result in a potential scarcity of usable nest sites. 



In areas where large amounts of habitat have been 

 removed, it is likely that there is significant saturation of 

 the habitat by murrelets. In Washington, Oregon, and 

 California, approximately 85 percent of the historic 

 old-growth has been removed. If the Marbled Murrelet was 

 not limited by nesting habitat previously, certainly the 

 chances of limitation have greatly increased today. If habitat 

 is saturated, then the remaining stands in these three states 

 should have maximum densities of murrelets. Data from 

 Alaska suggest that murrelet density may be higher when 

 the availability of suitable nesting habitat is restricted. For 

 example, Kuletz and others (this volume) compared onshore 

 dawn activity with offshore populations in the Kenai Fjords 

 and in Prince William Sound. They found generally higher 

 onshore populations in the Kenai than in the Sound, although 

 the at-sea population in the Sound was much higher. They 

 suggested the difference in numbers at sea was due to the 

 relative abundance of good nesting habitat in the Sound, 

 whereas the Kenai had relatively disjunct, smaller patches 

 of large trees. We interpret the apparently higher number of 

 detections on shore in the Kenai Fjords as a result of 

 crowding into the limited number of sites available, rather 

 than in a difference of the quality of the available nesting 

 areas. More indirectly, evidence for packing into a habitat 

 is found in an area of northwestern California, in the largest 



area of coastal old-growth forest that remains south of 

 Puget Sound. That area, in the vicinity of Redwood National 

 Park and Prairie Creek State Park, has the highest rate of 

 murrelet detections of any area within the species' range, 

 with detections often exceeding 200 per morning (Miller 

 and Ralph, this volume). This may reflect packing into the 

 remaining habitat, or it may reflect superior habitat that has 

 always supported large numbers of birds, although we do 

 not think the latter is the case. Even if nesting habitat is in 

 general saturated, it is also probable that there will be years 

 when suitable nest stands are unoccupied by murrelets. 

 Absences could result from the temporary disappearance of 

 inhabitants from the stand due to death or to irregular 

 breeding, perhaps because of a temporary decline in prey 

 resources. Under either of these circumstances, unoccupied 

 stands would not necessarily indicate that, over a longer 

 time scale, habitat was not limiting or that these stands 

 were not part of the murrelet' s habitat. 



Behaviors The behaviors that influence site fidelity 

 and use, as well as the degree of coloniality, will affect the 

 likelihood of occupying of new habitat, and both may 

 influence the rate that birds displaced by habitat destruction 

 will acquire new nesting grounds. Site fidelity is the 

 propensity of breeding birds to return to the same nesting 

 location year after year, whereas philopatry is the tendency 

 of young birds to recruit to the area where they were raised. 

 Coloniality, the clumping of nests in time and space, is a 

 function of the number of nests likely to occur in a stand. 

 Most seabirds show considerable site fidelity, and many 

 individuals return to the same nest site annually (Divoky 

 and Horton, this volume). The young of many alcid species 

 recruit to their natal colonies, although the degree of 

 philopatry can be as low as 50 percent. Previously unoccupied 

 habitats are occupied and new colonies grow faster than can 

 be accounted for by recruitment. As Divoky and Horton 

 (this volume) discuss, from what we know of other seabirds, 

 we can assume that Marbled Murrelets return to a stand 

 once they have bred there and continue to use that stand at 

 least as long as they breed successfully. Upon nest failure, 

 they may change nest sites or mates, but they would be 

 expected to remain in the stand. Thus, once a stand is 

 occupied by murrelets, one would expect it to be used on a 

 regular, if not annual, basis, so long as it is not modified. 



Marbled Murrelets do not form dense colonies as is 

 typical of most seabirds. However, limited evidence suggests 

 that they may form loose colonies or clusters of nests in 

 some cases. We would expect to find that the species 

 maintains low nest densities, commensurate with available 

 habitat. Coloniality evolves either as a means of protection 

 against predation, or as an adaptation to exploit shared 

 resources (nesting or foraging). We have no evidence that 

 murrelets engage in group defense against predators, and 

 their reliance upon cryptic coloration to avoid detection 

 would argue for a wide spacing of nests to prevent predators 

 from using area-restricted search, or from forming search 

 images for murrelet nests. Marbled Murrelets have a number 



14 



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



