One of Madagascar’s glamour birds, the Sickle-billed Vanga, is one of the most artistic and recently generated results of evolution in the world of birds.
By Rex Graham
The various shapes of bills of the 15 species of Galapagos Finches inspired Darwin’s concept of evolution. However, an even greater variety of bills has emerged among the 22 species of insect-eating vangas endemic to Madagascar. The evolutionary stories of these vangas are helping scientists understand both the tiny steps evolution can take and also those of continental-scale involving large groups of related birds, including the 300 species of the insect-eating Ovenbird (Furnariidae) Family in the Americas.
About 29 million years ago, the first vanga landed on Madagascar. It was love at first bite. The island had large migratory birds and raptors, but no smaller rainforest birds. As a result, the forests were a smorgasbord of succulent insects high and low.
“Vangas have evolved to fill a diverse range of niches,” said 3 experts on Tropical insect-eating birds in the journal Biological Conservation. “The vangas of Madagascar are perhaps even more ecologically versatile than the Furnariidae.”
After vangas arrived, scientists said their rate of speciation exploded. Today, birdwatchers see the results of the explosion in the toucan-like Helmet Vanga, bark-creeping Nuthatch Vanga, aerial Flycatcher Vanga and the ground-foraging Crossley’s Vanga.
Vangas actually had two phases of evolution. The pace of the initial one slowed as new species took advantage of almost all of the available ecological opportunities. However, some insects remained an untapped food resource.
Quite unexpectedly, speciation surged again about 10 million years ago, according to a team of European and U.S. researchers reporting in Proceedings of the National Academy of Sciences of the U.S.. That’s when a “key innovation” in thinner and curved beak designs breathed new life into vanga diversification.
“It is not only the design of the bill that matters, but also the way it is put to use,” the scientists said. Some vangas began to resemble and behave like woodcreepers in the Ovenbird (Furnariidae) Family. This second wave of vanga evolution generated probers that search for insects and other invertebrates hiding in, on and under tree bark.
Rise of the curve
The pinnacle of the probers is the Sickle-billed Vanga. It is the largest and one of the most recently evolved species, and arguably the most beautiful. It is the only one with a strongly decurved bill. It’s not strong enough to be used as a chisel to remove bark, but it doesn’t need to be. The bill is a forceps that lets the vanga extract arboreal cockroaches, crickets and spiders from the holes and cracks of dead trees and branches.
Sickle-billed Vangas often roost at night in flocks of about 20 birds and tend to scatter in the morning in smaller groups. While foraging, they hang upside-down and insert their slender bills into holes and cracks. They especially like dead trees or dead limbs on live trees that have been taken over by complex communities of wood-boring insects.
Riflebirds in Australia and Woodhoopes in Africa are those areas’ versions of the Sickle-billed Vanga. The Hoopes of Africa, Asia and Europe use their curved bills to probe holes in the ground.
No curve, no problem
There are no sickle-billed finches on the Galapagos Islands. However, the Woodpecker Finch has developed an idiosyncratic equivalent. “A twig or cactus spine is used by the bill as a tool to provoke emergence of insect larvae from their galleries deep within branches,” Galapagos bird expert Peter Grant said in the journal Acta Zoologica Sinica. Even if never exposed to the tool use and in the presence of adults that did not use them, Woodpecker Finch chicks somehow learned on their own by trial-and-error. Mental skills can compensate for the lack of a specialized bill.
I believe that the more we watch, photograph, protect and study Sickle-billed Vangas, the better for the species, all birds, all wildlife and all humans.