Chapter 7 



Breeding and Natal Dispersal, Nest Habitat Loss and 

 Implications for Marbled Murrelet Populations 



George J. Divoky 1 



Michael Morton 2 



Abstract: Evidence of breeding and natal dispersal in alcids is 

 typically provided by the resightings of banded birds, the establish- 

 ment of new colonies, and/or evidence of immigration to established 

 colonies. The difficulties in banding, observing, and censusing 

 Marbled Murrelets at nesting areas preclude using any of these 

 methods for this species. Based on the limited number of nests 

 observed in consecutive breeding seasons, breeding site fidelity 

 (birds breeding in the same nest as the previous year) may be lower 

 than most other alcids. This is likely due to low breeding success 

 associated with high levels of nest predation. By contrast, annual 

 use of nest stands suggests fidelity to a nesting area may be high. 

 Natal dispersal, the breeding at locations away from their fledging 

 site, is likely similar to that of other alcids. Loss or degradation of 

 previously occupied nesting habitat will result in the displaced 

 breeders prospecting for new nest sites. In areas with no unoccu- 

 pied available habitat, this could result ia birds being prevented 

 from breeding, attempting breeding in ..uboptimal habitat, or in- 

 creasing the distance dispersed from the previous breeding sites. 

 Each of these is likely to result in a decrease in reproductive 

 output. Dispersal patterns need to be considered when assessing 

 the importance of stands and the status of populations. The small 

 population size and fragmented nature of the remaining breeding 

 habitat could increase the time required for prospecting birds to 

 locate recently matured old-growth forest, resulting in underesti- 

 mating the importance of a stand. Additionally, birds could be 

 dispersing from regions of high production of young to areas with 

 low production but where recruitment opportunities are higher, 

 partially hiding the low reproduction of the latter population. 



The ability of Marbled Murrelets to disperse from natal 

 sites, and their fidelity to breeding sites or stands, has important 

 implications for the potential of the species to respond to 

 habitat loss and colonize or reestablish breeding areas when 

 habitat has been altered. With knowledge of these factors, 

 we could more accurately assess the effects of habitat 

 destruction on the viability of populations throughout the 

 species' range. In the discussion below, we examine what is 

 known about dispersal in other alcid species and the possible 

 implications for the Marbled Murrelet. 



Dispersal of birds can occur both by established breeders 

 changing breeding sites (breeding dispersal) and by birds 

 nesting away from their natal nesting area (natal dispersal) 

 (Greenwood and Harvey 1982). The degree of nest-site fidelity 

 by established breeders can be expected to be related to 

 previous breeding success and the frequency of change in 

 availability of suitable nest sites and prey resources. Nest 



1 Wildlife Biologist, Institute of Arctic Biology, University of Alaska, 

 Fairbanks, AK 99705 



2 Wildlife Biologist, U.S. Fish and Wildlife Service, U.S. Department 

 of Interior, 2800 Cottage Way, Room El 803, Sacramento, CA 95825 



site availability can be decreased both through the destruction 

 of nest sites and through chronic predation. An increased 

 rate of natal dispersal should be related to the potential to be 

 more successful in finding mates or nest sites away from the 

 natal nest site or colony. 



Breeding Dispersal 



Breeding site fidelity in a long-lived species, which the 

 Marbled Murrelet is presumed to be (Beissinger, this volume), 

 can provide benefits in increased breeding success and 

 lifetime fitness. Site fidelity can reduce potential reproductive 

 effort by (1) increasing the chances of breeding with the 

 previous year's mate, (2) eliminating or reducing the need 

 to locate a suitable nest site, and (3) allowing the development 

 of familiarity with the marine and terrestrial environment. 



The rate of breeding dispersal is low for most alcid 

 species that have been studied. Rates of nest-site fidelity of 

 previously breeding alcids are: 91 .5 percent Razorbills (Alca 

 torda) (Lloyd 1976); 96 percent Common Murres (Uria 

 aalge) (Birkhead 1977); 93.2 percent Atlantic Puffins 

 (Fratercuia arctica) (Ashcroft 1979), 57-95 percent Black 

 Guillemots (Cepphus grylle) (Divoky, unpubl. data; Petersen 

 1981); 86 percent Pigeon Guillemots (C. columba) (Drent 

 1965); 78 percent Ancient Murrelet (Synthliboramphus 

 antiquus) (Gaston 1992). 



The degree of breeding dispersal displayed by an alcid 

 should be related to the rate that nesting habitat is created 

 and destroyed, the level of mortality of breeding birds, and 

 the availability of nest sites. Species with a high probability 

 of returning to a nest site destroyed over the winter would 

 have fewer reasons to have evolved site tenacity. Harris and 

 Birkhead ( 1 985) suggested that the Thick-billed Murre (Uria 

 lomvia) might show less site tenacity than other Atlantic 

 alcids because rockfalls destroy or create nest sites in their 

 colonies more frequently than for other species. Burrow 

 nesting alcids could be expected to show higher rates of 

 breeding dispersal than talus nesters due to the higher 

 frequency of collapse of burrows. 



Annual overwinter mortality could be expected to 

 influence breeding site fidelity. High overwinter mortality 

 would decrease the chances of a surviving bird being able to 

 breed with the previous year's mate and, by creating more 

 vacancies at established nest sites, increase the opportunities 

 for dispersal for species that are nest site limited. 



For those alcid species in which breeding site fidelity 

 has been examined, and for birds in general (Greenwood and 

 Harvey 1982), changes in nest site are more frequent after a 

 breeding failure. For Black Guillemots, nest-site fidelity 

 was 92 percent for successful pairs and 48 percent for failed 



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



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