Where is the pink pigeon found and what threats does it face?
The pink pigeon is found on the island of Mauritius, formerly home to another pigeon, the Dodo, now extinct. There are only around 400 birds left in the wild and about another 70 in captivity in zoos and wildlife parks around the world.
Until humans arrived in the 1600s Mauritius was quite literally a paradise island – no predators, no people and lush forests.
Humans hunted the Dodo for its meat. Luckily for the pink pigeon its flesh is often toxic and can induce stomach cramps and vomiting and so the settlers quickly learnt to leave them alone.
But some of their other actions had a drastic impact on the bird.
Humans unknowingly introduced four non-native predators – rats, cats, mongoose and crab-eating macaques – to the island. All prey on pink pigeons. Humans also decimated the pink pigeons’ habitat, clearing lush forests to make room for tea and sugar cane plantations. Today Mauritius has only 2% of its native forest remaining.
By introducing species of non-native birds to the island settlers also, inadvertently, introduced a pathogen – disease causing micoorganism – that proved near fatal to the pink pigeon. Trichomonas gallinae is a protozoan parasite and kills over 50% of all pink pigeon squabs (young).
Finally, because of population decline pink pigeons have low genetic diversity and suffer from inbreeding depression. These are negative effects produced when closely related individuals reproduce.
Have Pink Pigeons been close to extinction before?
It’s almost certain that pink pigeon numbers have been decreasing since the arrival of humans in the 1600s. But the population crashed in the 1970s leaving less than 20 birds.
A conservation programme, started by the Durrell Wildlife Trust and Mauritian Wildlife Foundation, captured the remaining birds and started a captive breeding programme on Mauritius. The birds were intensively managed and reintroduced back into the wild in the 1980s where they continued be closely monitored.
In the early 1990s disaster struck again – caused mainly by feral cat predation – and the population crashed to about nine birds. Volunteers and researchers from the Trust and Foundation, led by Professor Carl Jones, used innovative captive breeding strategies such as removing eggs or newborn chicks from pink pigeons and giving them to Barbary doves to foster, so that the pink pigeon parents could breed again. This breeding, followed by closely monitoring the re-introduced individuals, enabled the pink pigeon population to recover and reach its current population level in 1999.
A genomics conservation project has been launched to rescue them. Why did you take this route and how does it work?
The pink pigeon is a conservation success story. But the work to save the species is by no means over. The Mauritian Wildlife Foundation works incredibly hard to manage and conserve the small remaining population. They control predators, treat sick individuals and provide supplementary feed. But, despite all these measures, the population has been unable to grow further and they struggle to even maintain current levels in the wild. This is not surprising when you consider that over 50% of eggs laid by pink pigeons don’t hatch and juvenile mortality is exceptionally high due to the impact of inbreeding depression, disease and predators.
That’s why we’ve embarked on a genetic rescue mission. The process involves adding new gene variants to a population by either natural immigration of individuals from separate populations or through reintroduction and translocations of individuals.
Research suggests that captive population of pink pigeons found in zoos and wildlife parks around the world – which was established as early as 1977 and unlike the in situ captive breeding programme has remained isolated – harbour genetic variation that the wild population lacks.
It’s our hope that by reintroducing individuals with new gene variants back into the wild we can reverse the negative effects of inbreeding and introduce alleles – different forms of a gene – that will increase disease resistance and overall genetic diversity. This will provide pink pigeons with the ability to adapt to any further challenges it faces.
Is there evidence of this working with other animals?
But what’s interesting is that there are very few examples of genetic rescue being used. In fact there are many more scientific papers discussing genetic rescue than examples of it actually being applied.
There are less than 30 examples of genetic rescue, encompassing vertebrates, plants and invertebrates. This may be because scientists have been cautious in this field to avoid any possible negative effects. For example, a decrease in the fitness of a population through the introduction of detrimental genetic variants.
A recent study by Professor Richard Frankham, an expert in the field of conservation genetics, showed that in over 94% of cases of genetic rescue, the results have been incredibly beneficial. He argues that the reluctance to use the technique can’t be justified scientifically.
The pink pigeon is an ideal candidate because we already have a lot of information about the species. This includes genome sequences from museum specimens – birds that were alive in the 1800’s before the population crash. This will allow us to thoroughly screen any candidates and ensure the gene variants we are reintroducing back into the wild population were there previously and are not, for example, variants that have helped a pink pigeon adapt to a life in captivity. These could be harmful to wild pink pigeons who obviously face different challenges to captive ones.By Camilla Ryan and Matt Clark for The Conversation Africa