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