Population Dynamics in Northern Marine Birds 



by 



William H. Drury 



College of the Atlantic 

 Bar Harbor, Maine 04609 



Abstract 



It seems only reasonable to assume that populations of marine birds fluctuate 

 even when not disturbed by man; such fluctuations would result both from the 

 secondary effects of species adaptive tactics and from changes in the marine 

 environment. I briefly review some human activities and some other natural pro- 

 cesses that have resulted in changes in numbers and distribution of seabirds and 

 present a short discussion of theoretical models which emphasizes that conclu- 

 sions drawn or predictions made from models of the dynamics of populations 

 depend upon the assumptions about stability that were used in preparing the 

 models. I then review those special characteristics of seabirds which are directly 

 relevant to planning programs intended to protect seabirds or encourage their 

 increase and identify several goals for improving our understanding of the popu- 

 lation dynamics and biology of marine birds. My general conclusion is that 

 enough is already known to undertake effective conservation programs, and that 

 time is pressing. 



Seabirds have been categorized as renew- 

 able resources in only a few places, although 

 their symbolic value has been recognized for 

 centuries (for example, the medieval poem 

 "The Seafarer" and the designs on Saint 

 Cuthbert's tunic). With the exception of the 

 Russians (Belopol'skii 1961; Uspenski 1956), 

 the Australians (Serventy 1967), and the Ice- 

 landers, industrialized peoples have not con- 

 sidered seabirds to be salable and therefore 

 worth managing. Yet during many centuries 

 the seabirds of the northern seas were a major 

 food for coastal and island villages (Bent 

 1919, 1921, 1922; Fisher and Lockley 1954). 



Some biological principles that affect the 

 dynamics of seabird populations are identified 

 in this paper. I believe these principles must 

 form the basis of plans to maintain and in- 

 crease seabird numbers. 



I describe some observations of population 

 changes, review briefly the conflicting theo- 

 retical frameworks for population dynamics, 

 and identify some of the biological character- 

 istics of marine birds that affect the way in 

 which population changes occur. The terms 

 "seabirds" and "marine birds" are used inter- 



changeably for those bird species which de- 

 pend upon salt water for some part of their an- 

 nual cycle (c.f., the Pacific Seabird Group). 



Population Fluctuations 



Broadly stated, the populations of northern 

 seabirds have shown marked short- and long- 

 term fluctuations. Most authors have as- 

 sumed that all such fluctuations reflect 

 human disturbance of the natural system, be- 

 cause of the obvious effects of human preda- 

 tion during the last 200 years. 



Human Impact 



In the centuries before people traveled ex- 

 tensively between islands, seabirds were 

 taken in ways that we judge must have 

 allowed the survival of the colonies (e.g., those 

 at the Faroes or Saint Kilda, those in Iceland 

 and Greenland, or those in the Aleutian Is- 

 lands and the Bering Strait). We presume 

 either that the populations of island peoples 

 were regulated by shortage of resources other 



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