Aerial view of Fregate Island home to 59 warblers translocated in 2011; photo credit David Wright
The movement of individuals of an endangered species to a new location to establish a new population is a common tool used by conservationists worldwide. Creating new populations increases the total number of individuals alive and also reduces the risk of extinction by increasing the number of independent populations. This is especially important for small, isolated island populations of rare species which may have filled all available habitat but cannot colonise new islands by themselves.
A lot of careful planning is needed to successfully establish a new population by translocation. In many cases, translocations experience problems with low survival of the released individuals, or the failure of the population to breed and grow successfully over time. Studying translocations is therefore very important to help scientists improve the outcome of this kind of conservation work.
The warblers were placed in travel boxes for their helicopter ride to Fregate photo credit Tatiana Raposo
One key consideration that may affect the long term survival of a new population is how much genetic variation it contains. Genetic variation is important as without it populations can suffer problems such as inbreeding depression and may not be able to adapt to new challenges, such as new diseases – which is bad news if you are trying to conserve a species! It is important that we can measure how much genetic variation is within a translocated population to make sure we have taken all the possible variation that existed in the original population.
The Seychelles warbler was once considered one of the rarest birds on Earth. By the 1960s it was reduced to just one population on Cousin Island. Since then, careful management by BirdLife International and then later Nature Seychelles has been remarkably successful in helping to conserve this species and Cousin was soon full up with around 350 birds.
Warbler being released on Fregate Island photo credit Paul Nixon
Nature Seychelles, the BirdLife International Partner in Seychelles, initiated a translocation program with technical assistance from the Seychelles warbler study group. This program successfully translocated the warbler to four new islands: 29 birds were moved to Aride in 1988, 29 to Cousine in 1990, 58 to Denis in 2004 and finally 59 to Frégate in 2011, all from the original population on Cousin. On the new islands the populations have grown quickly and there are now around 3000 warblers across these five populations.
By using genetic markers and immunity genes we were able to look at the genetic variation across the populations. We found that we have managed to capture nearly all of the variation present in the Cousin population and take it to each new population. Crucially, each new population received all of the immunity gene variation, meaning they have the best possible defence against any new diseases they might encounter.
Ringed and ready for release photo credit Tatiana Raposo
We also found that the levels of variation are stable, thanks to the fast growth of the new populations. Additionally, taking lots of individuals from Cousin has not caused any loss of variation in this original population. The key message is that the translocations can be considered extremely successful in the short-medium term. Long-term persistence is of course never certain, but our analysis suggests that the populations have the best possible start for the future.
Our findings are published in the scientific journal Molecular Ecology and can be accessed freely online at
http://onlinelibrary.wiley.com/doi/10.1111/mec.12740/abstract.
By Dr. David J. Wright (Centre for Ecology, Evolution and Conservation, University of East Anglia UK)