From Neotropics to Afrotropics: Rainforest birds and ecological niches

Guest writer: Luke L. Powell

Sunrise over rainforest canopy in the Brazilian Amazon.
Sunrise over rainforest canopy in the Brazilian Amazon.

Back in the fall of 2012, I was wrapping up my last of four field seasons in the Central Amazon – Manaus, Brazil. My study site, the Biological Dynamics of Forest Fragments Project, was set up for its remoteness: “MOTFA” is what we replied when asked where we worked: Middle Of The F&%*ing Amazon.

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One of our more simple field camps near Manaus, Brazil – pretty basic living.

I spent the early part of my career very much focused on those rainforest birds of the Central Amazon – the antbirds and ovenbirds and woodcreepers and all the rest. I had previously worked in Costa Rica as well as Peru, so in Manaus I had some idea of what I was getting myself into bird-wise. In other words, within the Neotropics (tropics of the Americas), the families, and often the genera of birds that frequent rainforests are pretty consistent. Despite the diversity of Manaus, my experiences elsewhere in the Neotropics had prepared me somewhat for what to expect from the birds – which bird families were where, which would be sensitive to rainforest degradation, and which families and genera held which niches.

Fast forward a couple of years and my research has moved from the new to the old world tropics. When starting this transition, I was curious to see if the patterns that I understood from the Neotropics would hold in the Afrotropics – Equatorial Guinea in particular. Why Equatorial Guinea you say?! Well, this Massachusetts-sized country nestled squarely in western central Africa has the full complement of African rainforest fauna: elephants, chimps, gorillas and a dizzying array of colorful birds. But the wildlife is under intense threat from development: Equatorial Guinea discovered oil in the 1990’s and has since been pumping oil, laying down asphalt and putting up buildings as quickly as they can. Several parks were also set aside, but it’s not clear what the sensitive bird species even are or how good of a job those parks actually do at protecting those sensitive species. To fill the gaps of knowledge in this rapidly-developing country, colleagues and I started the Equatorial Guinea Bird Initiative – an NGO dedicated to exploration, education and ecology in the country. We’ve since expanded to mammals as well and changed the name to Biodiversity Initiative.

When I set off for my new project in Equatorial Guinea, the birds were entirely different and I pretty much had to start from scratch on understanding the community. You see, the African and South American continents split off such a long time ago that the bird communities have diverged to a tremendous agree, so much so that most of the families in the Neotropics don’t even exist in the Afrotropics. Fortunately for me, in most cases, there are very close yet unrelated analogs holding the same ecological niches—the role that an animal plays in the rainforest community.

The first place I looked was to the canopy—for an analog of those loud, colorful, Neotropical fruit-eaters with enormous bills: toucans. And immediately I was satisfied in finding that hornbills – the ecological equivalent of toucans – are both abundant and species rich in Equatorial Guinea. This represented a beautiful example of convergent evolution: when two unrelated species converge to fill a similar niche and body plan; dolphins and sharks are a classic example. Unfortunately, because of their large body size, the largest hornbills are often shot by hunters seeking bushmeat. As Africa continues to develop, fewer and fewer of these charismatic hornbills will remain.

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Me holding an African Pied Hornbill (Tockus fasciatus) in Oyala, Equatorial Guinea

Next I looked to the understory, where in the Neotropics, ovenbirds and antthrushes accounted for much of the diversity. In the Afrotropics this primarily niche is filled by an unrelated family: the (Old World) thrushes (Turdidae). The American Robin (in the US) and European Robin are well known members of this family. These birds are stocky with a prominent chest, and strong legs and feet built for hopping and walking along on the forest floor – just like their Neotropical counterparts.

Forest Robin (Stiphrornis erythrothorax) captured and banded in Equatorial Guinea
Forest Robin (Stiphrornis erythrothorax) captured and banded in Equatorial

But what about mixed species flocks? In the Neotropics, these multi-species groups of insectivorous species are dominated by the antbirds (Thamnophilidae) with Thamnomanes antshrikes leading the charge with their whip-crack calls. African mixed species flocks are dominated by the greenbuls (Pycnonotidae), a cryptic group of often greenish-colored birds that are ubiquotous in the mid story. Though far less is known about these Afrotropical assemblages of mixed-species flocks, in the Eastern Arc Mountains of Tanzania, The Square-tailed Drongo (Dicrurus ludwigii) has recently been found to be the flock leader. Although not a greenbul, this drongo (family Dicruridae) does make a whip-crack rallying call like its Neotropical flock-leading counterpart.

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Flock-leading Dusky-throated Antshrike (Thamnomanes ardesiacus) banded near Manaus, Brazil.

And what about the Neotropical warblers (Parulidae) – those nimble insect-gleaning gems? In Afrotropical rainforests, these are matched by the Old World Warblers (Sylvidae), a drabber but ecologically equivalent family that are also common tropical-temperate migrants – with many of these breeding in Europe. And the ultra-diverse aerially acrobatic Neotropical Flycatchers (Tyranidae)?

In the Afrotropics these find an ecological equivalent in the Old World Flycatchers (Musicapidae), like the oft-studied Pied Flycatcher
In the Afrotropics these find an ecological equivalent in the Old World Flycatchers (Musicapidae), like the oft-studied Pied Flycatcher

If you’ve spent enough time in Neotropical forests (or you had a great guide on your bird tour), you’ve eventually stumbled on the Old Man of the Forest – the trogon. Most are in the genus Trogon and all are frugivorous and strikingly bright, beautiful canopy birds. Much to my delight, I found that this family exists in the Afrotropics and is no less spectacular. Equatorial Guinea has two species in the genus Apaloderma, one of which was caught by my field crew just last week. I’ve since learned that the Asian tropics (my next frontier?) have a few species of trogons as well – most in the genus Harpactes.

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Ornithologist in training Amancio Motive Etingüe holds a Bar-tailed Trogon (Apoloderma vitattum) near his home town at Ureka, Bioko Island, Equatorial Guinea

And last but certainly not least, my favorite Neotropical bird family (or subfamily, depending on your taxonomy) is the curiously-moving woodcreepers (Dendrocolaptidae). These ovenbird relatives have modified claws and stiffened tails that they use to hitch themselves vertically up trunks and branches gleaning insects from the bark as they go – not unlike creepers and nuthatches of temperate forests. In Manaus there are 13 species of woodcreeper, each of which has its own unique and curious niche. Strangely enough, this group seems to have no ecological equivalents in Afrotropical rainforests! There certainly a few woodpecker species in Equatorial Guinea, but none are particularly common aside from perhaps the Buff-spotted Woodpecker (Campethera nivosa). Why this niche is essentially empty is a mystery to me, but it sure seems there’s a big haul of Afrotropical insects on tree trunks that are not well exploited.

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The Duke of Woodcreepers: Red-billed Woodcreeper (Hylexetastes perrotii) captured near Manaus, Brazil. Note the unusual green skin on the feet and around the eye.

So I’ve found that there are tons of cool birds in the Afrotropics – most with ecological niches similar to that of an analogous family in the Neotropics, and at least one group (the woodcreepers) without. What is a clear difference between Neotropical and Afrotropical communities is how much more poorly the Afrotropical species are understood. With development booming in Africa and human population on the continent projected to quadruple by 2100 – much faster than any other continent – there is a great need to understand and protect these African birds. For me, Equatorial Guinea is a microcosm of the situation in the rest of Africa, which is one of the reasons I am now focused there. What are the keystone species such as flock leaders (drongos?) and seed dispersers (hornbills)? Which species and ecological groups are most vulnerable to disturbance such as logging and agriculture (terrestrial insectivores? large, hunted species?). How many cryptic species exist – those that look alike but are unique species only differentiable by song? Are the birds of isolated islands such as Bioko, Equatorial Guinea, subspecies, or are they actually full (and endemic) species worthy of protection as such? With more work, we can understand the ecology, evolutionary history and habitat requirements of many of these poorly known Afrotropical gems, which will help us to protect them in this time of intense change in Sub-saharan Africa.

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A sacred Bubi forest in Equatorial Guinea, Africa.

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