Brilliant birds and the mystery of the mutating mangroves

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Under the Banyan, Trinidad

Scarlet ibises in the Caroni Swamp / Credit: Charles J Sharp / Wikimedia Commons (left); Fernando Flores / Creative Commons (right)

As dusk falls over the Caroni Swamp on the west coast of Trinidad, hundreds of scarlet ibises fly in from their feeding grounds to roost in mangrove trees that grow in the dark, brackish water. The birds settle in the branches like glowing embers.

The scarlet ibis recently received official designation as an environmentally sensitive species, with Agriculture Minister Clarence Rambharat warning of hefty fines for anyone found to have threatened the birds, according to local news reports. That's just the latest move to protect a species that has had a unique imprint on the region.

For generations, local people hunted these birds for their meat and used their feathers for Carnival costumes. In the 1860s, colonial records warned that “a fierce war” had been waged on the ibis and that it would soon be very rare, according to a researcher writing for conservation organization Birds Caribbean. But it is thanks to a hunter, Simon Nanan, that the bird has a haven today.

In the 1930s, Nanan started guiding fishermen and duck hunters into the maze of waterways that run through the Caroni Swamp – some 6,000 hectares of marshes, mudflats and mangrove forest. Many of his clients marvelled at the scarlet ibis so he began offering tours to see the birds. These proved more popular than his hunting trips, and so ecotourism was born in Trinidad.

In time, Nanan convinced the colonial authorities to create a sanctuary to protect the scarlet ibis. The bird now shares its umbrella of security with a rich variety of wildlife that includes silky anteaters, crab-eating raccoons, spectacled caimans and nearly 200 bird species. The Caroni Swamp also provides key services to local people by protecting the coastline from storm surges, providing a nursery for fish and shellfish and supporting a thriving tourism industry.

When Trinidad gained its independence in 1962, it made the scarlet ibis its national bird and banned hunting of the species. But old habits die hard, and poaching has continued. Eating ibis is regarded locally as a status symbol.

Under the new protections that come with ESS status, anyone caught harming, trading or in possession of the species now faces a fine of 100,000 Trinidad and Tobago dollars (about US$15,000) or up to two years in prison. The penalties apply to possession of even a single feather. What few people realise is that those scarlet feathers have another story to tell.

In the late 1990s, researchers noticed harmful genetic mutations in mangrove trees in areas where the ibises roosted. They discovered that the sediment beneath the trees had abnormally high levels of mercury, as did the feathers of the scarlet ibises — unlike those of some other birds in the Caroni Swamp.

Unlike the other birds, the scarlet ibises also travelled to wetlands in Venezuela each year, where they fed on crustaceans and other animals, the researchers noted. They concluded that mercury used by gold miners far inland had entered the country’s rivers and made its way into the food chain. Feeding on contaminated animals is what led the mercury to build up in the bodies of the scarlet ibises, the researchers surmised.

Back in Trinidad, moulted feathers accumulating around the roost over decades appear to have polluted the sediment around the mangroves and resulted in the trees' genetic mutations. This 20-year-old scientific detective story takes on new relevance given the massive increase in mining and illegal use of mercury underway in Venezuela.

If Trinidad’s new penalties do not deter poachers and consumers of ibis meat, perhaps the risk of exposure to mercury will.

A flock of Scarlet ibises / Credit: Aaron Maizlish / Creative Commons 

 

This story is produced under the EJN Biodiversity Fellowship 2018. It was first published on Under the Banyan