The threats leading to population declines in birds are many and varied: agriculture, logging, and invasive species are the most severe, respectively affecting 1,126 (77%), 763 (52%) and 473 (32%) globally threatened species. These threats create stresses on bird populations in a range of ways, the most common being habitat destruction and degradation, which affect 1,354 (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 1,126 threatened birds (77%) at risk, logging and wood harvesting impacting 763 species (52%) and invasive species which threaten 473 (32%) of threatened species (BirdLife International 2016). In addition, residential and commercial development, hunting and trapping, livestock and ranching, and climate change are having serious negative impacts (see figure). While all of these threats have additive negative effects on species, climate change in particular often exacerbates other threats. All of 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 by anthropogenic activities like logging and agricultural expansion) currently impacts 1,354 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, even stochastic, unpredictable events like natural disasters (e.g. volcanoes, cyclones, drought) or pressure from problematic native species (e.g. increased competition or hybridisation) become very difficult to combat. Within healthy populations these threats may be more benign.
Related Case Studies in other sections
Compiled: 2004 Last updated: 2017
BirdLife International (2017) A range of threats drives declines in bird populations. Downloaded from http://www.birdlife.org on 24/02/2018