Bird Populations (Collins New Naturalist Library, Book 124)
Ian Newton
Language: English
Pages: 608
ISBN: 0007527985
Format: PDF / Kindle (mobi) / ePub
Earlier naturalists formed the impression that bird numbers remained more or less stable through time. In the years since these words were written, however, changes have occurred in the landscapes of the British Isles and in the seas around our coasts, causing bird populations to fluctuate in an unprecedented way.
In Ian Newton’s latest New Naturalist volume, he explores bird populations and why their numbers vary in the way they do, from year to year or from place to place. He addresses the various factors that we know limit bird numbers – food supplies and other resources, competitors, predators, parasites and pathogens, and various human impacts.
The combination of a rapidly expanding human population, a predominantly utilitarian attitude to land, central government policy on land use, and increasing mechanisation have combined to promote more massive changes in land use – and hence in bird habitats – in recent decades than at any comparable period previously. These developments have in turn brought huge changes in bird populations, as some species dependent on the old landscapes declined, and others benefiting from the changes increased. Over the same period, changing public attitudes to wildlife, protective legislation and a growing network of nature reserves allowed previously scarce bird species to recover from past onslaughts, while climate warming has promoted further changes.
In this seminal new work, Ian Newton sets out to explain why different bird species are distributed in the numbers that they are, and have changed over the years in the way that they have. He emphasises the factors that influence bird numbers, rather than the numbers themselves, thus providing a much-needed overview which is necessary if we are to successfully manage bird populations, whether for conservation reasons, for sustainable hunting or for crop protection. The continued monitoring of bird numbers can also alert us to impending environmental problems. In addition, the regular watching and study of birds now provides a source of recreation and pleasure for very large numbers of people, who would find a world with fewer birds a poorer place.
yet other bird populations, changes in breeding numbers from year to year were associated with changes in both breeding and mortality, which together caused an increase or decrease in numbers. They included species that ate the same type of food year-round in the same area (such as some owls dependent on voles, Chapter 4) and other species in which changes in breeding numbers were affected by conditions in both breeding and wintering areas (such as the White Stork, mentioned above). FIG 11.
before the next year by immigration of surplus birds from other areas. In effect, gamekeepers are harvesting such populations, reducing predation on bird eggs in the process, but causing no obvious overall long-term population decline. In the case of the target game species, the gamekeeper gains the advantages from repeated short-term reductions in corvid numbers, but little or no longer-lasting benefit. In contrast, the killing of raptors in the past eliminated most such species from large parts
affected a wide range of species from doves to gamebirds, but waterfowl are the main casualties. Once in the gizzard, spent gunshot is gradually eroded and absorbed, but the resulting poisoning may not become evident until 2–3 weeks after ingestion. The complete absorption of 1–3 lead pellets (depending on their size) is considered sufficient to kill any waterfowl species from duck to swan. The initial symptoms are fairly obvious. The bird may be reluctant to fly when approached, and may droop
Associations Ornithologiques, Colmar, France, pp. 166–72. Strann, K. B., Vader, W. & Barrett, R. T. (1991). Auk mortality in fishing nets in north Norway. Seabird 13, 22–9. Suddaby, D. & Ratcliffe, N. (1997). The effects of fluctuating food availability on breeding Arctic Terns Sterna paradisaea. Auk 114, 524–30. Suhonen, J., Alatalo, R. V., Carlson, A. & Höglund, J. (1992). Food resource distribution and the organisation of the Parus guild in a spruce forest. Ornis Scand. 23, 467–74.
years in two areas of similar habitat on Salisbury Plain in southern England (Tapper et al. 1996). Predator killing was undertaken in one area for three years, leaving the second area as a control, and then switched to the second area, leaving the first as the control. Predator removal was done mainly in spring and involved chiefly Foxes, Carrion Crows and Magpies, whose spring densities were thereby much reduced. These operations led to significantly improved nest success and brood sizes among