Declines can be quick and catastrophic
 Tony Palliser/BirdLife International
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Certain bird species are showing very rapid and severe population declines. This is worrying: history tells us that even formerly abundant species can go extinct if the causes of their declines are not addressed promptly.
Widespread declines in birds are indicative of global problems
Bird populations are declining across many regions and habitats of the world. Indeed it has been estimated that, globally, bird populations have declined 20–25% since pre-agricultural times as a result of conversion of natural habitats by humans. Population declines for suites of species that depend on particular habitat types (such as waterbirds: see pdf case study, box 1), indicate that these ecosystems are deteriorating globally and require conservation attention.
Declines can be precipitous
Population declines are not always slow and gradual, in line with progressive habitat loss or exploitation — on occasions, they can be extremely rapid and dramatic. Such precipitous declines can affect even formerly abundant species (box 2). We need to detect and respond promptly to these declines if we are to address the underlying causes, prevent extinctions and avoid disruption of ecological systems. This requires regular and reliable monitoring of populations, and sufficient resources to identify and implement appropriate conservation measures to halt and, eventually, reverse declines.
Apparently slight disturbances can sometimes be catastrophic
Threats need not be direct (e.g. through hunting), nor particularly extreme, to have a profound impact on bird populations. This is particularly so for large-bodied, slow- breeding species, where even quite small increases in mortality among adults may sometimes lead to significant population declines (box 3). For these species, the underlying causes are likely to have been operating for a while by the time declines are detected, and, even if remedial action is taken immediately, recoveries may not be seen for many years.
Boxes: case studies and scientific analyses
Download SOWB pp.10–11 (PDF, 340 KB) containing the following:
1. Waterbirds are showing widespread declines
More than a third of 346 populations of Anatidae for which trends are known are in decline
2. Precipitous declines of Indian vulture populations
Number of Gyps vultures decline between 1991-1993 and 2000
3. All albatrosses species are in alarming decline
Nos. 1960s to present, 3 spp. at Bird Island, South Georgia