Brilliant birds and the mystery of the mutating mangroves

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

For generations, local people hunted these birds for their meat and used their feathers for Carnival costumes. By the 1860s, colonial records warned that “a fierce war” had been waged on the ibis, and that it would soon be rare. Yet it is thanks to a hunter that the bird has a haven today.

In the 1930s, Simon Nanan started guiding fishermen and duck hunters into the maze of waterways in the Caroni Swamp – some 6000 hectares of marshes, mudflats and mangrove forest. Many of Nanan’s clients marvelled at the scarlet ibis, so he began offering tours to see the birds and these proved more popular than his hunting trips. And so, ecotourism in Trinidad was born.

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. It protects the coastline from storm surges, provides a nursery for fish and shellfish, and supports 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 to the present day. Serving and eating the bird has apparently become a status symbol. In response, the government this week increased protection for the species.

Anyone caught harming, trading or possessing the species now faces a fine of 100,000 Trinidad and Tobago dollars (about US$15,000) and 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 showed that the sediments 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 swamp.

The researchers noted that, unlike the other birds, the scarlet ibises travelled to wetlands in Venezuela each year, where they fed on crustaceans and other animals. 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, they surmised.

Back in Trinidad, moulted feathers accumulating around the roost over decades appear to have polluted the sediments and resulted in the genetic mutations in the mangrove trees. 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.

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Reference: Klekowski, E.J. et al. 1999. An association of mangrove mutation, scarlet ibis, and mercury contamination in Trinidad, West Indies. Environmental Pollution 105: 185-189. https://doi.org/10.1016/S0269-7491(99)00028-7

Photo credits: Bottom — Top left — Charles J Sharp / Wikimedia Commons; Top right — Fernando Flores / Creative Commons; Aaron Maizlish / Creative Commons

Scientists reveal yet another reason fig trees are titans of biodiversity

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Biologist David Mackay got a surprise when he began studying the birds visiting fig trees in his native Australia: While he expected to see plenty of species coming to eat the figs, he didn’t expect the insect eaters to outnumber them two-to-one.

Mackay already knew that figs feed more bird species than any other fruit. His research, published in June, would show that fig trees are disproportionately important for insect-eaters too. It adds to growing evidence that fig trees are titans of biodiversity with important roles to play in conservation.

What makes fig trees so crucial is their ancient relationship with tiny wasps. The trees depend on the wasps to pollinate their flowers, while the wasps can only breed and lay eggs inside their partner’s figs. Thanks to this partnership, figs are available year-round and have been called ‘keystone’ resources for fruit eaters. Mackay’s study is the first to show that fig-wasps emerging from figs before they ripen are also valuable year-round resources for a diverse variety of insect-eating birds.

Altogether, Mackay recorded 55 bird species visiting Ficus rubiginosa fig trees to feed on insects. They included ten species — such as the superb fairy-wren and the shining bronze-cuckoo —whose recent declines in numbers have concerned conservationists. Mackay and his colleagues say fig trees are “very likely” to be similarly important to insect-eating birds throughout tropical, subtropical, and temperate regions globally.

To support this view, Mackay points out that in just his study and two others in localised areas of India and Costa Rica, researchers have already identified more than a hundred insect-eating birds visiting fig trees. “The presence of avian insectivores in figs in these three continents strongly suggests their occurrence in figs is ubiquitous,” he says.

“I can hazard a wild guess that there are at least several hundred species of insectivorous birds that forage in fig trees worldwide,” Mackay told me. “This has important implications for the conservation of insectivores, many of which have suffered and continue to suffer declines in response to habitat loss and fragmentation.”

As Mackay points out, the number of fig-wasps emerging from figs on a single Ficus rubiginosa tree in just a few weeks could approach ten million. He adds that insect-eating bats would also relish fig-wasps, many of which fly at night. His study adds to a growing body of evidence that fig trees are centrepieces of vast food webs that include tens of thousands of species.

“I suspect fig trees could play an important role in conservation of declining insectivores as well as contributing to the conservation of other species in the wider communities they inhabit, including frugivores and the other plants that depend on them for seed dispersal,” Mackay said.

Increasingly, researchers and conservationists are turning to fig trees to boost rainforest regeneration by attracting seed-dispersers. Mackay said that using fig trees could also slow or even reverse declines of insect-eating birds: “If we don’t do these restoration projects with figs then we stand a chance of losing these birds altogether.”

This post was first published by Mongabay.com on 6 July 2018 and is reproduced here under a Creative Commons licence.

Read more about the ecological and cultural importance of fig trees in my book, published in the UK as Ladders to Heaven and in North America as Gods, Wasps and Stranglers.

Reference

Mackay, K.D., Gross, C.L. & Rossetto, M. 2018. Small populations of fig trees offer a keystone food resource and conservation benefits for declining insectivorous birds. Global Ecology and Conservation. Published online on 20 June 2018. https://doi.org/10.1016/j.gecco.2018.e00403

Photo credits

Left to right —  Superb fairy wren (Malurus cyaneus): Patrick_K59 / Wikimedia Commons; Eastern yellow robin (Eopsaltria australis): Graham Winterflood / Wikimedia Commons; Eastern spinebill (Acanthorhynchus tenuirostris): DavidFrancis34 / Wikimedia Commons

Who eats figs? Everybody

“The proper way to eat a fig, in society,” wrote DH Lawrence, “is to split it in four, holding it by the stump, and open it, so that it is a glittering, rosy, moist, honied, heavy-petalled four-petalled flower. … But the vulgar way, is just to put your mouth to the crack, and take out the flesh in one bite.”

I’m a vulgar fig-eater. Few things give me more pleasure than when I bite into a ripe one and eat it up. With the right fig, the flavours can be so intense, so rich that it seems clear to me that no other fruit can compare. But the figs I eat are of just one of nearly a thousand fig species, and what eats the others is really interesting.

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