Conceding extinction: a look at rare birds

When do you throw in the towel and concede that a rare species has gone extinct? A new study in the journal Biological Conservation presents a methodology for helping conservationists answer this difficult question.

Chris Elphick and fellow researchers tested the method on 38 rare species and subspecies of birds from North America and Hawaii. Based on their analysis they concluded that all 38 have likely gone extinct. This includes a number of species, which have not officially been declared extinct such as the Bachman's warbler (Vermivora bachmanii)

The method uses sighting records - i.e. the years in which a species has been observed - to infer whether species have gone extinct and when the extinctions occurred. For each species, they looked at the average gaps in time between sightings and the date of the last recorded observation, and based on statistical analysis they estimated a likely extinction year.  If the estimated extinction date was in the past, then the species is likely gone. If the estimated extinction date is in the future, then the species may still have a fighting chance.

The process is more than just an academic exercise. Searching for potentially extinct species and trying to conserve them can both be very expensive endeavors. This methodology allows conservationist to identify the species least likely to have gone extinct and prioritize resources for them while minimizing what we spend on species that are already gone.

Of the birds they analyzed, only one species, the 'Alala from Hawaii, had a predicted extinction date in the future - 2013 - at a 95% confidence level which means that it is the least likely to be extinct. All the other species with predicted extinctions after the year 2000 were located in Hawaii: the oloma‘o population on Moloka‘i (Myadestes lanaiensis rutha), Maui ‘akepa (Loxops coccineus ochraceus), po‘ouli (Melamprosops phaeosoma), ‘o'u (Psittirostra psittacea) on Kaua‘i, and Kaua‘i ‘o‘o (Moho braccatus).

The study identified some interesting patterns in avian extinction in North America and Hawaii. They found evidence for a peak in extinctions around 1900. On average, 4 years passed from the time of a species last sighting to its estimated extinction date. Conversely, long gaps of time between sightings were very rare. These findings give a chilling reminder of the urgency of species conservation work.

--Reviewed by Rob Goldstein

Elphick, C., Roberts, D., & Michael Reed, J. (2009). Estimated dates of recent extinctions for North American and Hawaiian birds Biological Conservation DOI: 10.1016/j.biocon.2009.11.026