For long-lived, slow-breeding birds, such as albatrosses, even apparently slow population declines means they face a high risk of extinction.
For long-lived, slow-breeding birds, even apparently slow population declines can have alarming consequences if sustained. Three such species are Wandering Albatross Diomedea exulans (total population 27,600 mature individuals), Grey-headed Albatross Thalassarche chrysostoma (250,000) and Black-browed Albatross T. melanophrys (>1 million), which all breed on islands in the southern oceans (Croxall and Gales 1994). At Bird Island (South Georgia), long-term monitoring studies have revealed steady declines of 1.8%, 2% and 4% per year respectively for these species over the last 20–30 years, caused by reduced survival of adults and, particularly in the last 1–2 decades, also of juveniles (Croxall et al. 1998, also British Antarctic Survey unpublished data, see figure). For Wandering Albatross, declines have been in the region of 4–5% since 1997.
These seemingly modest annual declines are highly significant, since albatrosses take many years to produce enough offspring to replace themselves. These albatrosses may have generation lengths of up to 30 years, so these declines equate to population reductions of 30–65% over 65 to 90 years (i.e. three generations). Incidental mortality linked to longline and trawl fishing is the greatest threat to albatrosses. Because of these high rates of mortality and population decline, all three albatrosses mentioned above are evaluated as globally threatened: despite still appearing numerous, they face a high risk of extinction if current trends continue (BirdLife International 2008).
Related Case Studies in other sections
Compiled 2004, updated 2008
BirdLife International (2008) Many albatross species are in alarming slow decline. Presented as part of the BirdLife State of the world's birds website. Available from: http://birdlife.org/datazone/sowb/casestudy/116. Checked: 01/08/2014