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W. H. DRURY 



rows (Zonotrichia albicollis), hermit thrushes 

 (Catharus guttatus), and dark-eyed juncos 

 (Junco hyemalis) has resulted in new nesting 

 records of more northerly species, also in 

 southeastern New England. 



The ability (or lack of ability) of some or- 

 ganisms to expand their ranges over time has 

 been a subject of consideration for a number 

 of years by plant and animal geographers. An 

 important botanical paper on this subject in 

 the Bering Sea region was presented by 

 Hulten (1937), who analyzed the ranges of 

 plants of the area of Kamchatka, eastern Si- 

 beria, Alaska, and northwest Canada, show- 

 ing that diverse floras occur in some re- 

 stricted geographic areas. He called these 

 areas "refugia," and postulated that many 

 species had survived Pleistocene glaciations 

 in them because these refugia remained ice- 

 free. He, like Fernald (1925), was puzzled as to 

 why only certain species had been able to ex- 

 pand their ranges outward from these "areas 

 of persistence," while other apparently more 

 "conservative" species were unable to do so. 

 Similarly, there appear to be conservative en- 

 demic bird species of the Bering Sea region: 

 the extinct Commander Islands cormorant 

 (Phalacrocorax perspicillatus), Steller's eider 

 (Polysticta stelleri), spectacled eider (Lampro- 

 netta fisheri), emperor goose (Philacte cana- 

 gica), whiskered auklet (Aethia pygmaea), 

 least auklet (A. pusilla), parakeet auklet (Cyc- 

 lorrhynchus psittacula), Aleutian tern (Sterna 

 aleutica), red-legged kittiwake (Rissa brevi- 

 rostris), bristle- thighed curlew (Numenius 

 tahitiensis), long-billed dowitcher (Limno- 

 dromus scolopaceus), surfbird (Aphriza vir- 

 gata), black turnstone (Arenaria melano- 

 cephala), rock sandpiper (Calidris ptiloc- 

 nemis), and western sandpiper (C. maun). 



The ranges of horned puffins (Fratercula 

 corniculata), Kittlitz's murrelet (Brachy- 

 ramphus brevirostris) and, perhaps, crested 

 auklet (Aethia cristatella) suggest that some 

 species of "Beringian" seabirds have ex- 

 panded their ranges from Hulten's (1937) 

 "refugia." 



Dispersal and Regional Persistence 

 of Marginal Populations 



The presence of several subelements of a 

 species population and, therefore, the oppor- 



tunity for dispersion among alternative breed- 

 ing sites may be an important factor in the re- 

 gional persistence of a species on the margin 

 of its range, as illustrated by the history of 

 laughing gulls (Larus atricilla) in New 

 England. 



Between 1875 and 1900 there were fewer 

 than 50 laughing gulls in Massachusetts 

 (Mackay 1893) and about 35 in Maine (Norton 

 1924). In Massachusetts the laughing gulls all 

 settled on one large island, Muskeget, where 

 by 1940 there were about 20,000 pairs (Noble 

 and Wiirm 1943). Meanwhile, in Maine the 

 population had been disturbed by sheep and 

 men and had shifted about among seven is- 

 lands. The Maine population grew to only 

 about 350 pairs by 1940 (Palmer 1949). 



The laughing gull population in both States 

 has decreased since 1940. In Massachusetts, 

 where all pairs occupied one island, the popu- 

 lation had fallen to about 250 pairs by 1972, 

 but the Maine population, still divided into 

 five colonies, stabilized at 250 pairs (i.e., the 

 same as instead of only 1% of the Massachu- 

 setts population). 



Use of General Principles in 

 Solving Conservation Problems 



Game biologists have successfully main- 

 tained the populations of hunted animals by 

 using a number of classical principles of game 

 management. They have controlled mortality 

 by regulating kill and have increased standing 

 stock by improving habitat on a local scale. 

 This seems to have worked in species which 

 are short-lived, have large clutch sizes or 

 litters, and which occupy mosaics of highly 

 productive "successional habitat." Seabirds, 

 however, contrast with these species in a num- 

 ber of important biological characteristics. 

 They have small clutches, postpone breeding 

 until they are several years old, and are sub- 

 ject to periodic or chronic reproductive fail- 

 ures. Therefore, their populations are skewed 

 toward older animals and replacement of lost 

 individuals is slow. Many seabirds, like some 

 geese, have a high level of site tenacity and 

 thus may resist recolonization or fail in the at- 

 tempt to recolonize a breeding site once elimi- 

 nated from it. In those species studied it ap- 

 pears that the breeding birds at a small per- 



