[Our intrepid scientist Steffen Oppel assesses the conservation prospects of the Montserrat oriole. And after all that intensive fieldwork, he really does deserve a cold drink!]
You would think that being confined to a tropical island surrounded by the turquoise Caribbean and enjoying balmy temperatures year-round isn’t such a bad deal. And it generally isn’t. In fact, life on some Caribbean islands is so pleasant that many birds and reptiles never left once they had settled there, and so we now find lots of species that are endemic to a single island.
The Montserrat oriole is one of these – endemic to a single island, the UK Overseas Territory of Montserrat. But the oriole isn’t exactly enjoying a lavish lifestyle in a pleasant spot. A few hundred years ago humans discovered the island, cut down the forest, and brought animals that never used to be on Montserrat, such as cats, rats, pigs etc. Worse still, in 1995 a volcano erupted and burnt down more than half of the forest where the Montserrat orioles used to live. The species has been teetering on the brink of extinction ever since.
Male Montserrat oriole (Steffen Oppel)
The RSPB entered the race to save the oriole in 1999. After a decade of field research, laboriously crawling through dense tropical forests, up and down steep and rugged slopes and ravines, and counting and observing the birds, we recently compiled all the collected information to assess how likely it is that the Montserrat oriole will survive. Five years of nest monitoring told us that the species does a lot better in years when it rains more – they can lay more eggs and re-nest quicker when they lose a nest (the rats are rather good at destroying nests!) We don’t know why, but it is possible that in years with more rain there is simply more food and water available for the birds, and they are in a better body condition.
But then there are the years when the volcano rumbles. Every few years the magma that piles up on top of the active cone collapses and sends a giant ashcloud into the sky. If the oriole is desperately unlucky, this ashcloud falls out over the last patch of forest left standing on the island. This happened in 2001, 2003, and most recently in 2010, and usually resulted in the forest being covered in a layer of fine ash several cm thick. The ash is very acidic and kills leaves and invertebrates, so the orioles are probably struggling to find food. We found that mortality in those volcano years was about 20% higher than in normal years. So the Montserrat oriole population is on a bit of a roller-coaster ride – up in good years with plenty of rain, and down in years when the volcano spews ash.
Montserrat's volcano - on an angry day (Steffen Oppel)
For the time being, and with a patch of about 1200 hectares of forest still somewhat intact, the oriole is able to withstand these external forces. The population has fluctuated in the past 10 years, but has not decreased any further. Because we will never be able to manage rainfall or the volcano, we need to make sure that the Montserrat oriole population has as much suitable habitat as possible. That means protecting every bit of forest left standing on Montserrat, not only for the birds, but also for other endemic species – and to ensure a clean water supply for the people living on Montserrat.
After all, you wouldn’t want to be stranded on a Caribbean island with nothing to drink except rum...