Vulnerability of Birds to Extinction

According to the world extinction trend, 50% of critically endangered bird species are predicted to go extinct in 5 years; 20% of endangered species in 20 years, and 10% of vulnerable species will be extinct in 100 years. As for all other birds not on the IUCN list, extinction may happen within the next 800-2800 years (Crosby et al. 1994).

Furthermore, the extinction trend was shown to be non-random and concentrated in certain genera and families. For instance, the flightless birds, the non migratory water birds, and birds with beautiful plumage (parrots) are most vulnerable.

Furthermore, certain life history traits make some species more extinction-prone than others. Extinction risk will be higher for specialised species than generalists; species with small populations, small geographic ranges, and poor dispersal ability. Species with low fecundity, and long generation times are predicted to be at most risk because they would recover slowly from a severe reduction in population size and remain threatened longer by demographic and stochastic factors. Species with high offspring production, short generation times, and small body size, are predicted to be less susceptible to extinction because they are not as prone to large stochastic population fluctuations. High levels of local bird endemism coupled with increasing rates of forest change mean that more PNG species are likely to become threatened in the near future

Life histories do not act in isolation to cause extinction; rather they are influenced by environmental stochasticity as well as human activities. Crosby (1994), upon quantification of extinction threats showed that 51.9% of threats were from the loss and alteration of habitat, 23.2% by small ranges and or small populations, and 7.6% through hunting, persecution, accidental trapping and subsistence egg collecting. Predation and displacement by introduced species made up 5.8% of threats while commercial egg collecting accounted for 2.6%, natural causes 3.3% and other threats 3.1%.

Activities such as human persecution and introduced predators are harmful for taxa that have slow rates of population growth by disturbing the balance between the fecundity and longevity of such species. In contrast, sources of extinction risk that reduce niche availability, through habitat loss, represent a threat to taxa that are ecologically specialized.

According to the threat quantification data, over half of the current threats on birds are happening because humans are interfering with the habitat of these birds.

Archaeological evidence suggests that birds have been made extinct through selective over-harvesting by humans. However, current trends show that birds are often threatened with extinction because humans are having a detrimental impacts on their ecology and the threat is exacerbated when the birds have limited adaptability and hence resilience to withstand environmental.

Furthermore, more bird extinctions (83%) have occurred on oceanic islands than on the continents. New Guinea is itself a large island positioned between Australia and Asia. Mayr and Diamond (1976) also observed that the New Guinea montane forests are like islands separated by a sea of forest and therefore suggested that the Theory of Island Biogeography and extinction risks are relevant to these “islands”. Islands of habitat can also be created by human activities.

Ref:
CROSBY, M. J., STATTEERSFIELD, A. J., COLLAR, N. J. & BIBBY, C. J. (1994) Predicting avian extinction rates. Biodiversity Letters, 2, 182-185.
MAYR, E. & DIAMOND, J. M. (1976) Birds on islands in the sky: Origin of the montane avifauna of Northern Melanesia. Proceedings of the National Academy of Sciences of the United States of America, 73, 1765-1769

%d bloggers like this: