March 26, 2021
ANTBIRDS AND A BIRDING HOLY GRAIL MOMENT IN NORTHERN PERU
By Andrew Whittaker
Before my first visit to South America over three decades ago, I still vividly remember excitedly thumbing through my crisp new field guide, Birds of Colombia, by my now good friend Steve Hilty and William Brown. Each superb plate was like another piece of candy that made my mouth water at the incredible avian diversity and the many fabulous species I would be seeing soon. I found new (to me) bird families particularly fascinating. Some had rather odd names—cotingas, trogons, jacamars, manakins—and, of course, it was these brightly colored and exotic birds that seemingly jumped off the plates!
However, to be honest, I was kind of apprehensive at seeing page after page of similar looking species. So much so that I began to have panic attacks wondering how on earth I would ever be able to identify these in the field, in particular, a profusion of dull look-alike birds called antbirds! I knew from watching BBC natural history films as a boy that the biomass of ants and termites in rainforests was incredibly high, with lots and lots of ants for them to eat, so why not diversify! Before moving to Brazil to work on the Amazonian birds for the WWF, Steve’s excellent Colombian field guide became my bible, never leaving my side, and what an incredible help it was!
Most species of antbirds are sexually dimorphic (male and female plumages are distinctly different). Males in general are gray, black, and white, whereas females are brown, rufous, and buff. They range in size from the impressive Giant Antshrike of southern South America, which is the size of a large cuckoo (12 inches), to tiny antwrens (3.5 inches), which can be some of the most challenging to identify.
Antbirds are insectivores, feeding almost entirely on arthropods, which they snatch from live or dead leaf surfaces of trees and bushes, or even off the forest floor’s leaf litter.
Most birders visiting the Neotropics dream of experiencing what I describe as one of the “Holy Grail moments” in any birder’s life: walking down a secluded forest trail and encountering an active army ant swarm! Army ants are dominant invertebrate predators in tropical rainforests. When hundreds of thousands of army ants are on the move, it’s like a giant vacuum cleaner killing and consuming every insect, spider, small snake, and lizard in its path! Soldiers, with their larger jaws, cut the largest items into manageable parts, which are then returned, by smaller workers, to the bivouacs often hundreds of meters away to feed the queens and her grubs.
To witness such an event is truly mesmerizing, as I did on my Northern Peru trip a few years ago, where I took these photos of White-plumed Antbird and Zimmer’s Antbird.
As can be seen from this photo of a Zimmer’s Antbird, ant-following antbirds feed, not on the ants, but on arthropods fleeing from the ants. Anyone who has looked for an army ant swarm knows how hard they can be to locate! How do the obligate ant-followers find these nomadic swarms? They use the vocalizations of conspecifics as cues to find these ever-moving ant swarms in the vast rainforests. As first light hits the forest floor, they cover great distances, flying and calling to one another and searching.
The army ants have two phases of activity—a nomadic (wandering) phase and a stationary (statary) phase—that constantly cycle. The nomadic phase begins around 10 days after the queen lays her eggs. This phase will last approximately 15 days to let the larvae develop. This is the phase the birds need, as the ants move during the day, capturing mostly arthropods to feed their broods. At dusk, the ants will form their nests or bivouacs, which they change almost daily. It’s presumed that these obligate antbirds take advantage of collective knowledge to find army ant swarms. Some of the birds rely solely on one species of army ant. This makes the professional army ant followers sensitive to many of the very real threats to this ecosystem, like deforestation, global warming, and other similar issues. If anything affects the ant population, it could be devastating for these birds.
Another fascinating piece of ant information I will throw in here is related to frogs—honestly! Their consumption of small ants in South America is one of the principal ingredients allowing the famous and attractive poison dart frogs to produce their deadly toxic alkaloids. The toxicity is concentrated in their skin, and they certainly have evolved spectacular aposematic colorations to warn off any possible predators!
Amazingly, scientists banding songbirds in New Guinea in early 2000 made the almost unimaginable discovery of the world’s first poisonous bird! After being pecked and scratched by a jay-sized bird with an odd name, the Variable Pitohui (which drew blood), banders licked their wounds, causing grave swelling of their mouths, like a toxic reaction. Local hunters confirmed that the birds were in fact poisonous and should not be touched. The toxic poisons were present in the bird’s skin, feathers, and other tissues. After two years of careful research, a remarkable story unraveled; they were able to isolate and identify the compound responsible for the toxicity as a batrachotoxin neurotoxic steroidal alkaloid. Remarkably, this same toxic compound was first isolated from a Colombian poison dart frog, a Phyllobates terribilis! Pitohuis, like the frogs, sequester them from dietary sources, not from ants but a little-studied group of beetles, the genus Choresine (family Melyridae).
The natural world is truly fascinating and enriches our daily lives. I sincerely hope you and your families are all coping well, keeping safe and healthy in these extraordinarily difficult times. I certainly now have a much better understanding and appreciation of the incredibly strong migration urge that all of our migrant birds must feel each spring! I’m looking forward to being able to migrate myself again, and to sharing with our great VENT family our precious outdoors and wondrous wildlife.
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