Indian vulture populations have declined precipitously
Number of individuals No. of individuals
Puzzlingly, non-Gyps vultures and other scavengers in these countries remain unaffected, and reductions in food availability, or poisoning through exposure to pesticides, cannot explain the rapid and specific nature of the decline. Findings from examination of vulture carcasses from India were consistent with the agent being an infectious, probably viral, disease3. However, research in Pakistan implicates an anti-inflammatory painkilling drug, diclofenac, used widely in veterinary medicine in India and Pakistan in recent years4. Recent results indicate that this drug is a major cause of the observed vulture declines5. Experiments show that vultures are highly susceptible to diclofenac and are killed by feeding on the carcass of an animal soon after it has been treated with the normal veterinary dose. Modelling shows that only a very small proportion of livestock carcasses need to contain a level The number of Gyps vultures recorded along a standard set of of diclofenac lethal to vultures road transects in India declined dramatically between 1991– to result in population declines 1993 and 20001 at the observed rates. Additional 1991–1993 25,000 factors may influence Gyps 20,974 2000 20,974 populations and are subject to 1991–1993 20,000 2000 ongoing study, but there is no conclusive evidence at present 15,000 for other causes being involved. Unless the use of diclofenac is 10,000 urgently controlled, the 6,546 6,546 extinction of these vulture 5,000 species, all of enormous 883 517 ecological importance, seems 883 517 imminent. Indian and Slender-billed Vultures White-rumped Vulture 0
Albatross species are declining alarmingly
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 28,000 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 oceans1. At Bird Island (South Georgia), long-term monitoring studies have revealed steady declines of 1%, 2% and 4% per year respectively for these species over the last 2530 years2 (see figure). 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 3065% over 65 to 90 years (i.e. three generations). Data from other breeding sites show similar trends, indicating that these declines are likely to be occurring throughout the species ranges3. Incidental mortality linked to longline fishing is the single greatest threat to albatrosses (see p. 43, box 4). In the southern Indian Ocean, for example, illegal, unreported and unregulated fishing for the Patagonian toothfish Dissostichus eleginoides has killed an estimated 10,00020,000 albatrosses (mainly T. chrysostoma) annually since 19964. 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 continue3. SOURCES 1. Croxall & Gales (1998) Pp. 46–65 in Robertson & Gales, eds. Albatross biology and
Albatross species breeding at Bird Island (South Georgia) have declined steadily since the 1970s (the graphs show regression lines fitted to the annual census data) Wandering Albatross
1,600 1,400 1,200 1,000
500 400 300 200 100 0
300 200 100 0
conservation. Chipping Norton, Australia: Surrey Beatty & Sons. 2. Croxall et al. (1998) Pp. 69–83 in Robertson & Gales, eds. Albatross biology and conservation. Chipping Norton, Australia: Surrey Beatty & Sons. Also British Antarctic Survey unpublished data. 3. BirdLife International (2004) Threatened birds of the world 2004. CD-ROM. Cambridge, UK: BirdLife International. 4. CCAMLR (2002) Report of the twenty-first meeting of the Scientific Committee. Hobart, Australia: Commission for the Conservation of Antarctic Marine Living Resources. ACKNOWLEDGEMENT Data kindly provided by John Croxall (British Antarctic Survey, UK).
What birds tell us about conditions and change
Griffon vultures of the genus Gyps were formerly very common throughout South and South-East Asia, with White-rumped Vulture Gyps bengalensis considered one of the most abundant large birds of prey in the world. Vulture populations declined across much of the region in the first half of the twentieth century, but they remained common on the Indian subcontinent, where populations were maintained by an abundant supply of livestock carcasses. In the late 1990s, however, the Indian populations of White-rumped Vulture, Indian Vulture G. indicus and Slender-billed Vulture G. tenuirostris crashed, with dramatic declines also observed in Nepal and Pakistan. Survey work in India indicated that populations of these birds had declined by c.95% in less than a decade, between 1993 and 2000 (see figure) 1, leading to their classification in 2001 as Critically Endangered2.
Number of breeding pairs
and, even if remedial action is taken immediately, recoveries may not be seen for many years.
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,
State of the world’s birds 2004
Apparently slight disturbances can sometimes be catastrophic
White-rumped Vulture Long-billed Vulture SOURCES 1. Prakash et al. (2003) Biol. Conserv. 109: 381–390. 2. BirdLife International (2001) Threatened birds of Asia:
the BirdLife International Red Data Book. Cambridge, UK: BirdLife International. 3. Cunningham et al. (2003) Anim. Conserv. 6: 189–197. 4. http://www.birdlife.net/news/news/2003/06/vulture_update.html (June 2003). 5. Oaks et al. (2004) Nature (published online 28 January 2004, see www.nature.com).
Published on Oct 4, 2010
State of the world’s birds provides information on how birds can be used to focus action and as indicators to monitor change. Using the most...