308 



I.C.T.NISBET 



Perhaps the most significant gap in our 

 knowledge of North Pacific seabirds is in the 

 area of productivity and demography. As far 

 as I can judge, we know almost nothing about 

 the breeding success of these birds, their post- 

 fledging survival, their longevity, their age at 

 first breeding, the age structure of their popu- 

 lations, the fluctuations in their breeding per- 

 formance, or their survival from year to year. 

 For most species, we lack even the most basic 

 life history and life table information. 



If we can argue by analogy from studies 

 made in other parts of the world, including the 

 North Atlantic, we can make some basic 

 generalizations that we would expect to apply 

 to the birds of our area. We know that as a 

 class seabirds have some peculiar characteris- 

 tics which make them difficult to manage and 

 cause some of the problems we have in con- 

 serving them. In general, they are long-lived 

 and breed slowly, most lay small clutches, and 

 the historical experience is that they take a 

 very long time to recover from depletion of 

 population. Many have an irregular breeding 

 performance; some have long series of bad 

 years interspersed with occasional years of 

 good breeding success. Many seabird popula- 

 tions have traditionally fluctuated, as exem- 

 plified by those of the North Atlantic, whose 

 fluctuations were described by W. H. Drury 

 and W. R. P. Bourne. 



Some species of seabirds are conservative, 

 staying in the same colonies for many years or 

 generations. Others are volatile, dispersing 

 freely from one site to another and forming 

 new colonies in an unpredictable way. Sea- 

 birds exhibit a wide range of ecological adap- 

 tations; some are highly specialized, others 

 are highly generalized and adaptable. These 

 differences can be very important when their 

 environment changes, as D. N. Nettleship's 

 film "Puffins, predators, and pirates" graphi- 

 cally illustrated. 



As M. T. Myres pointed out on the 1st day 

 of the conference, seabird populations exhibit 

 both short- and long-term fluctuations. Long- 

 term fluctuations are those that take place 

 over times comparable to the generation time 

 of the species, which may be many years or 

 even decades for some seabirds. By surveying 

 populations and measuring changes in them, 

 we usually obtain information only about 

 long-term population trends, reflecting long- 



term changes in the environment. Short-term 

 perturbations in the environment are usually 

 not reflected quickly by changes in total popu- 

 lationcertainly not by changes that we can 

 measure with the accuracy of our present-day 

 census techniques. Many of the man-made 

 changes we are concerned about are short- 

 term. To identify their effects we should look 

 not for changes in total population but rather 

 for changes in biological parameters, such as 

 the first-year survival rate or the number of 

 young raised. I therefore suggest that some of 

 the most critical parameters to be measured 

 are changes in age structure of populations. 

 We should therefore select as biological moni- 

 tors species that can readily be aged for 

 example, gulls, which have a sequence of dis- 

 tinguishable immature plumages. 



In specifying gaps in our knowledge of the 

 ecology of birds, we should set clear priorities 

 rather than compile a long "shopping list" of 

 research projects. On the basis of the fore- 

 going survey, I would suggest the following 

 as priority items for further study. First, we 

 need to know a lot more about winter distribu- 

 tion, not only of the marine birds, but also of 

 inshore and coastal species. Second, we need 

 to study in greater detail the relation between 

 the day-to-day distribution of birds and the 

 local patchiness of the resources on which 

 they depend. Evidence that seabirds are able 

 to locate and use fluctuating and shifting food 

 sources has been given by several speakers at 

 the conference. We need to understand how 

 birds locate these resources and what relation 

 this has to their survival and vulnerability to 

 human activities. There is a special need to 

 study the ecology of endemic species because 

 their conservation is of special importance. 

 We need to learn more about the relation of 

 the birds to the commercial fisheries, both to 

 resolve existing or alleged conflicts and to 

 avert future problems. 



However, I believe that the highest re- 

 search priority should be given to obtaining 

 basic information on reproductive success and 

 life table data for some representative species. 

 Clearly, we cannot study many species in de- 

 tail, but in selecting key species for such 

 studies we should pick a variety of ecological 

 types for example, at least one generalist 

 species and one specialist, one sedentary 

 species and one migrant, one species at a high 



