The threats leading to population declines in birds are many and varied: agriculture, logging and invasive species are the most severe, respectively affecting 1,065 (87%), 668 (55%) and 625 (51%) globally threatened species. These threats create stresses on bird populations in a range of ways, the commonest being habitat destruction and degradation, which affect 1,146 (93%) threatened species.
There are a number of threatening processes driving declines in bird populations. Foremost among them are the spread of agriculture which puts 1,065 threatened birds (87%) at risk, logging and wood harvesting impacting 668 species (55%) and invasive species which threaten 625 (51%) of threatened species (BirdLife International 2008). In addition, residential and commercial development, hunting and trapping, changes to the fire regime, and pollution are having serious negative impacts (see figure). Climate change represents an emerging and increasingly serious threat to species; one that often exacerbates existing threats. All these threats are taken into account in the IUCN Red List evaluation of species and contribute to their classification as globally threatened (Critically Endangered, Endangered or Vulnerable). High-impact threats affect the majority of the population and cause rapid declines, while low-impact ones affect the minority and cause slower, albeit still significant, declines. These threatening process impact species’ populations in a number of ways (see figure). Habitat destruction and degradation (driven, for example, by logging and agricultural expansion) currently impacts 1,146 threatened birds (93%), while direct mortality and reduced reproductive success resulting from many of the processes listed above are affecting 54% and 33% of threatened species respectively (BirdLife International 2008).
Some threats can be reversed given enough resources, so targeted actions have been recommended for all threatened birds to directly address specific threats. When species populations become very small, however, incipient threats can emerge such as stochastic events (e.g.volcanoes, cyclones and drought causing mortality) or from problematic native species (e.g. increases in competition or hybridisation), that are difficult to combat; within healthy populations these threats may be more benign.
Related Case Studies in other sections
Compiled 2004, updated 2008
BirdLife International (2008) A range of threats drives declines in bird populations. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/120. Checked: 02/07/2016
|Key message: Human actions resulting in habitat destruction and degradation are the main causes of declines|