Birds of Iwokrama Forest
This summer, I joined a team of scientists and university students participating in a long-term study of the biodiversity of the Iwokrama Forest, a sustainable-use reserve covering almost one million acres in central Guyana. Iwokrama’s mission is to develop novel strategies to preserve biodiversity while also earning income from the forest, thereby demonstrating that it is possible to preserve functional ecosystems in the course of economic development.
I capture and band birds on study plots that I resample year after year to assess changes in species composition and abundance, and the age structure of populations. I also monitor avian diversity using automated sound recorders to document species at each site. The Iwokrama Forest boasts an impressive bird list – almost 500 species have been observed in the reserve!
Here I highlight some of the most interesting birds we captured this summer.
Antbirds are one of the most diverse bird families at Iwokrama, and we catch many in our nets. Students often ask me if they are called antbirds because they eat ants. The truth is much more interesting! Several species of antbirds are obligate army-ant followers. Army ants are common in rainforests of Central and South America, where they form large swarms that move across the forest floor, exploring every nook and crevice for prey.
No animal is safe from the ants – and as they attempt to flee, many are devoured by antbirds such as this Rufous-throated Antbird, one of two species of obligate army-ant followers at Iwokrama. These birds spend their entire day in the company of army ants, and their churring calls are a sure indicator that an ant swarm is nearby.
It is fascinating to watch these birds dart back and forth over the ants, clinging to vertical saplings with their powerful feet, snapping up insects as they try frantically to escape.
Although rainforests may look homogeneous, they are very complex places where many species coexist, often by specializing on particular resources.
The Black-chinned Antbird occurs only in a flooded forest, where it forages for insects in dense tangles along rivers and creeks. This specialization allows it to live in close proximity to other, ecologically similar species.
Within a single patch of rainforest, there can be several different vegetation types. One of the most common of these is seasonally flooded forest. During the annual rainy seasons at Iwokrama, the Essequibo River swells into the surrounding floodplain, bringing nutrients into the forest and influencing its structure and plant species composition.
Manakins are one of the most abundant birds in the forest understory at Iwokrama. This dazzling adult male White-crowned Manakin looks very different from his younger counterparts, which are clad in dull gray and green, resembling the females. Manakins are frugivores – their diet is almost entirely fruit – which means that they are constantly moving through the understory from one food source to the next, and this is why we catch so many of them in our nets.
Aside from eating, the most important activity in a male manakin’s day is displaying for females! Since fruit requires little effort to “hunt”, these birds can fill up fast and spend the rest of the day on their display perches, or leks.
Competition is fierce, and the end result is that the manakins include among their ranks some of the most beautiful plumages and complex displays in the bird world. This adult male – whose black body plumage still has a speck of green from his younger days – will glow iridescent blue on his display perch in the middle levels of the forest.
Here is one of the more bizarre birds we catch. The puffbirds are distantly related to kingfishers and resemble them in certain respects – both have large heads, oversized bills, and small feet, and both nest in cavities. But rather than hunting for fish along rivers and creeks, as kingfishers do, puffbirds are solitary predators of the forest, sitting still for long periods of time and darting out for large insects and small vertebrates such as lizards, frogs, and snakes. They spend so much time sitting still that they can easily be overlooked, and seeing one in the hand is a treat.
Puffbirds are named for their soft, lax plumage, and they often fluff themselves and open their bill when handled, as this one is doing.
The function of the curious notch on the tip of the bill is unknown – it could help them hold onto struggling prey, or perhaps it is used as a tool to dig their nest burrows, which are often in arboreal termite nests.
This bird puts on a show like no other – behold the Royal Flycatcher, an outlandish member of the most diverse bird family in the Neotropics, the Tyrannidae or Tyrant-Flycatchers. Although we catch relatively few species of flycatchers in forest understory at Iwokrama, this is the one we always hope to find in our nets! The spectacular crest is usually held flat along the top of the head, its colors subdued.
But when caught in a mist net, the Royal Flycatcher becomes a different beast entirely, as you can see here. The bird contorts itself, constantly turning its head almost completely upside down and from side to side, in a mesmerizing performance that will last for as long as it is handled.
Although the display is thought to be used in territorial encounters, few people have seen it in free-flying birds, since this species normally lives quietly in pairs along creeks and forest edges, where it is rather difficult to see. Royal Flycatcher nests are distinctive hanging structures, sometimes up to one meter long, usually placed over stream beds or narrow roads in the forest.
Many thanks to the staff of the Iwokrama Centre for Rainforest Conservation and Development, EPA-Guyana, the village of Surama, and to Operation Wallacea, for their support of my research.