If we are to measure population changes over the next few decades, it is of course essential to have a good base-line survey. However, I do not think it is either practicable or desirable to try to inventory the entire population of breeding seabirds with great accuracy. A more realistic and worthwhile program would be to select some sample colonies and to catalogue these sample areas in some detail, preferably with a photographic record, so that they can be resurveyed in later years to determine whether substantial population changes have taken place. Criteria for selection of sample colonies for inclusion in this base-line survey should include not only numerical size and species diversity but also ease of access, ease of observation, and the practicability of obtaining good photographic records.
Ecology and Functioning of the Resource
In the opening session of this conference, several speakers reviewed our general knowledge of the ecology of seabirds; others summarized our specific knowledge of the birds of the North Pacific, Bering, and adjacent seas, and their relation to physical and biological factors in the environment. There is no need to summarize these reviews again here except to point out that information on the relation between the birds and the marine environment is being generated very rapidly. We are beginning to understand the factors that control the breeding distribution of the individual species, their foraging strategies, and their dispersion at sea, at least in summer. However, it is clear from what has been said at this conference that we know much less about their ecology and distribution in winter. This lack of information is important because conflicting opinions have been expressed as to whether factors operating in the winter range or at the breeding colonies are more critical in limiting population size.
It is evident from what was said in the opening session that the distribution of the birds is very closely related to the distribution of marine resources. It is clearly no accident that the distribution of large numbers of many species of birds coincides with that of the major fisheries. Similarly, it is no accident that there is a relation between the distribution of birds and the extent of the continental shelf. These coincidences, which reflect the fundamental dependence of both birds and fish upon marine productivity, set the stage for existing and further conflicts between conservation of the birds and human exploitation of other resources of the area.
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 populations, the fluctuations in their breeding performance, 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 characteristics which make them difficult to manage and cause some of the problems we have in conserving 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 populations have traditionally fluctuated, as exemplified 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. Seabirds exhibit a wide range of ecological adaptations; 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" graphically 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 population—certainly 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 monitors species that can readily be aged—for example, gulls, which have a sequence of distinguishable 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 foregoing survey, I would suggest the following as priority items for further study. First, we need to know a lot more about winter distribution, 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.