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W. H. DRURY 



community. They pointed out that even 

 though the model is deterministic (i.e., as- 

 sumes that the system will come to equilib- 

 rium) the oscillations are so complex that they 

 may appear to be random, and it may be a 

 very long time before the system returns to a 

 position near its starting point. "On the other 

 hand a truly random ecological system could 

 always be fitted by a suitably ingenious limit 

 cycle. This suggests that ecological analysis 

 which does not consider component processes 

 must be viewed with great suspicion" (Gilpin 

 1975). May and Leonard (1975) and Gilpin are 

 both making a familiar point that neither 

 the logic nor the interactions described in a 

 formula will describe biological reality unless 

 the assumptions are correct. They are also 

 making a different point that an ingenious 

 mathematician can create a formula to de- 

 scribe almost any operation (whether its 

 workings are systematic or random), and the 

 formula may seem to work. 



Gilpin's moral is that one cannot learn very 

 much that is helpful by studying fluctuations 

 as such. One must study the factors control- 

 ling populations. This is a very old idea. 



It would appear that defining carrying 

 capacity and inherent rate of increase will not 

 be very instructive in managing seabird popu- 

 lations other than in speculating upon what 

 might be ideal upper limits. It can also encour- 

 age the musty sophistry that when a popula- 

 tion increases beyond this abstract carrying 

 capacity it "needs" to be hunted to prevent 

 overcropping resources and damage to itself 

 through a population decline. But we will not 

 have the time to carry out detailed studies of 

 life histories seeking for critical population- 

 habitat interactions over several fluctuations 

 for each species involved in a disaster before 

 designing programs to help seabird popula- 

 tions to build up their numbers. 



General Characteristics of 

 Marine Birds and Waterfowl 



Because general theory does not seem to 

 work and because detailed studies take too 

 much time, I conclude that it is necessary to 

 identify certain general principles upon which 

 to base applied programs. These categories of 

 knowledge include: (1) how vulnerable certain 



categories of seabirds, waterfowl, and shore- 

 birds are to specific types of disasters, (2) how 

 quickly their numbers build up after they 

 have been reduced, and (3) at what stages we 

 can help them best (i.e., at the breeding 

 grounds, at the winter gathering grounds, or 

 on migration). I believe that we already know 

 enough to design effective programs and to 

 begin work. To this end some characteristics 

 of seabirds are identified which determine the 

 population structures and ways in which their 

 numbers respond to changes in the en- 

 vironment. 



Habitat 



Although the shallow oceans, islands, and 

 seashores are among the most permanent fea- 

 tures of the earth in general, the details of 

 their numbers and distribution change 

 rapidly. Sandy shores are obviously being re- 

 worked even in the short span of a single life- 

 time. Distribution of islands and the sediment 

 load, extent, and strengths of currents vary 

 constantly in space and change with time. 



The food that seabirds use is patchy and 

 subject to both short- and long-term fluctua- 

 tions in numbers and shifts in geography. 

 Suitable breeding habitat is scattered, and in 

 many places where oceanic conditions provide 

 a good food supply there are no nesting sites. 

 Consequently, seabirds aggregate in colonies, 

 often dense, and the colonies are clumped for 

 geographical as well as biological reasons. 



Lack (1966) discussed some general features 

 of how the breeding adaptations of seabirds 

 are adjusted to the distances the birds must 

 go to find food. The species which feed close to 

 the nest characteristically establish isolated 

 territories or nest in small groups, and they 

 accept many different kinds of nesting sub- 

 strate. Their clutch sizes are large, individuals 

 move nesting sites readily, and their young 

 grow rapidly compared to the species which 

 feed far at sea. Species which feed far at sea 

 aggregate in large colonies. These species are 

 often rigid in their requirements for suitable 

 nesting sites, their clutches are usually 

 limited to one egg per season, their young 

 grow slowly, and there seems to be strong at- 

 tachment to traditional colony sites. 



