Birds as Monitors of Environmental Change

The need for environmental monitoring has never been greater. Burgeoning human populations, the greater demands they make on resources, and technological developments all result in massive and continuing increase in the impact of people on their environments. We have passed through a period in which environmental monitoring has had little academic respectability. This has been to some extent justified, for many monitoring programmes have had poorly-defined objectives and poorly-designed methodology, producing few or no useful results. Monitoring has also suffered because it relies largely on correlative analyses rather than on the manipulative experiments that have been more fashionable among ecologists.

In one sense the term ‘environment’ represents all elements of the biosphere, but it is often of more use in the narrower sense of those parts or attributes of a habitat that are functionally significant during all or part of an organism’s life. All living organisms have a range of tolerance for each environmental factor, though the limits and the optimum may vary between individuals and populations as well as between species. They may vary according to life stage or reproductive condition and because of interaction with other environmental factors. It is to environmental factors that populations and species respond, either through evolutionary change or through phenotypic plasticity. The response persists (and the population or species succeeds) where this has led to continued, indeed often enhanced, efficiency in utilizing the environment.

Several authors of books on the monitoring of pollution have advocated the use of animals as monitors in terrestrial and aquatic environments (e.g. Phillips, 1980; Schubert, 1985). Such studies tend to emphasize the use of sedentary invertebrate animals as biomonitors. By comparison, birds suffer from several apparent drawbacks. They are mobile, so pollutants will be picked up from a wide, often ill-defined, area; they are long-lived, so pollutant burdens may be integrated in some complex way over time; and they have more complex physiology, and so may regulate pollutant levels better then invertebrates. Furthermore, birds tend to be more difficult to sample, and killing birds may be unacceptable for conservation or ethical reasons. However, some of these characteristics may at times be positively advantegeous. Integrating pollutant levels over greater areas or timescales or over food webs, may be useful, provided that species are chosen carefully. Less sampling may be necessary if birds can reflect pollutant levels in the whole ecosystem or over a broad area. In addition, since they are high in food chains, birds may reflect pollutant hazards to humans better than do most invertebrates. It is also significant that birds are extremely popular animals with the general public, so pollutant hazards to them are likely to receive greater attention than threats to invertebrates.

Of the major classes of environmental contaminants, radionuclides tend to be generally less well known and less frequently studied than heavy metals or organic compounds. This may be because in the past elevated levels of environmental contamination with radionuclides have generally only been a problem in a relatively few and limited geographical localities. Most of these localities have either prohibited or greatly restricted public access because of safety and security considerations (e.g. nuclear weapons production or testing sites). As a result, the contamination of free-living flora and fauna with radionuclides has tended to be less apparent to both the scientific community and the public than contaminations with such substances as agricultural herbicides and pesticides. The latter, for example, may often produce the spectre of sick or dying birds in areas where they are commonly encountered by the public.

Throughout the world, birds are abundant, conspicuous and diverse components of freshwater ecosystems and of the wetlands and riparian areas around them. Although less than 4–5% of the Earth’s land surface is covered by standing freshwater, as many as 11–23% of all bird species use inland waters or their margins at some time during their annual cycle (Table 5.1). In part, this diversity reflects the fundamental importance, productivity and wider ecological influences of water in all biomes. It reflects also the riparian influence of running waters: Britain alone has 80 000 km of streams and rivers, yet river drainage from the whole of Europe still represents only 8% of the world’s total (Chorley, 1969).

For millenia humans have followed birds at sea to locate fish and mammals. Seabirds are highly visible wide-ranging upper trophic level consumers that can indicate marine productivity and biotic interaction. Compared with fish, marine mammals, and other animals that live primarily or exclusively underwater, seabirds are easy to survey, census and study. This chapter reviews the types, utilities and limitations of avian indicators of the condition of fish stocks and recommends research needed to improve understanding of avian trophic relationships.

An important reason for monitoring populations of birds is that their conservation is important in its own right. It is important to have a sufficient knowledge of underlying population processes to determine the probable causes of any population decline so that steps can be taken to halt or even reverse it. The subsequent success, or otherwise, of any action taken should be monitored.