bu-bu-bu-bu-bu-bu-bu! bu-bu-bu-bu-bu-bu-bu! From inside a dense thicket too tangled for me to walk into comes the rising, flutelike hooting of some unseen bird. I have no idea what it is, and have been trying for four months to find out. I’m in the tropical rain forest of northeast Honduras, the famed Miskito Coast, an area that is so unexplored and so high in biodiversity that the bird singing that song could be just about anything. I’m bursting to see it, but the bird remains hidden.
bu-bu-bu-bu-bu-bu-bu! I walk around the wall of vegetation and the singer just moves away, so that I never get a look. I circle back, and the wary singer dances away, singing, out of sight. Suddenly it dawns on me: just because I can’t walk in doesn’t mean that I can’t get in at all. I lie down on the moist ground and belly crawl through the leaves, eyes peeled for the mystery singer and also the feared fer-de-lance, a deadly snake whose bite on my face or arms would probably be fatal.
Crawl, listen, wait, repeat. I crawl toward the middle of the thicket, slower than a snake, pausing more often than I move, until finally a sudden flicker catches my eye. A small bird with a grayish back, buffy belly, streaked sides, and ridiculously long legs lifts it head and sings – bu-bu-bu-bu-bu-bu-bu! – I have him! Now, what the heck is it? After I crawl out (in reverse, no less), walk back to my cabin, and open several field guides I finally ID the mystery bird: Thicket Anpitta (Hylopezus dives). I look at the range maps and I’m ecstatic; this species isn’t supposed to be any closer than Costa Rica, two countries away. Tack on another discovery for the Miskito Coast!
Antpittas are one of those crazy birds that are only found in lowland tropical rain forests, where the diversity of plants, animals, bugs, and birds is through the roof. Every species has to have a niche, meaning the sum of the little habits, shapes, and diet that makes them so unique that they fit into the giant web of wildness with all their neighbors. Antpittas are shaped like miniature footballs with wings. One look is enough to tell a stark raving bird amateur that this is a species whose niche is on the ground.
If the Thicket Antpitta is the quintessential ground bird, what makes a canopy bird? That’s a harder question, and a really important one if you want to understand forest ecology. I have written about why canopy birds are important in other blogs. Without canopy birds the forest would pretty much shrivel up and die, literally. But who are the canopy birds? Lots of birds fly up and down through the forest. Are there some that belong to the canopy and not the lower layers? Fortunately, science has an answer.
If we divide a rain forest into layers – the ground, understory, midstory, and canopy (look here) research has shown that some birds are found way more often in the top of the forest than could ever happen by random chance. It comes down to numbers. If you flip a coin 100 times and 80 times it lands on heads, you are either really lucky or the coin is fixed. If you observe a particular bird species 100 times and it is in the canopy 80 times, that is no accident either. That bird is wired for the canopy. Take the Long-tailed Tyrant, for example. If you come to me and say you saw one near the ground, I will say that you have been smoking too many banana leaves. Some birds are so specialized for life in the canopy that they rarely, if ever, descend to the heights inhabited by mortal birds.
Here is another one. Green Shrike-Vireo. They are loud and bright, and you can spend days on the ground trying to see one and all you will get is a sore neck. Know what else? No scientist has ever seen the nest of this bird. Too high off the ground. Now that is a canopy bird!
Now here is where we get into evolution and ecology. Bear with me, because this is tricky. The Green Shrike-Vireo can’t be in all forests at the same time any more than you can, so let’s explain this from a human perspective. Let’s say you are perfectly adapted to living on a farm. You love the long hours, the machinery, the soil, and the crops, and your farm is in Iowa (my sympathies). You can’t run a farm in North Dakota at the same time. But you have cousins perfectly adapted to farming, they have the same name as you do (because they are related), and they have farms in North Dakota, Nebraska, California, and Washington. You and your cousins got farms covered.
The Green Shrike-Vireo has the canopy in Mexico covered. The Slaty-capped Shrike-Vireo has Brazil, and the Yellow-browed Shrike-Vireo has Colombia. They belong to the same family (Vireonidae, in bird terms) and they have the same name (Vireolanius is the genus). We say that the different Shrike-Vireo species replace each other in different parts of the world.
What’s more, lots of bird species replace each other like this, so much so that we can predictably describe the canopy bird community almost anywhere in the lowlands of the Neotropics by the group of birds you will find there, that are related, that play similar roles (eat small fruits vs. eat large fruits vs. drink nectar, etc.), but are different species. Whether you are looking at a forest canopy in Nicaragua, Brazil, or Surinam, you will have a largish pigeon in the genus Patagioenas, a large toucan (Ramphastos), a small toucan (Pteroglossus), an electrically colored tanager (Tangara), and so on.
The birds that replace each other are close evolutionary relatives. The forest needs a suite of bird species to fill certain ecological roles, say, to pollinate canopy plants or disperse canopy fruits and their seeds. There is a predictable suite of birds that get these jobs done. The forest is a large puzzle and all the pieces fit together. Until humans get in the way, and then some pieces get lost, and the puzzle stops looking like it should, and the game is over.
Below are two photo panels that tell the above story better than I just did. In the top panel are 6 bird species you could see in the forest canopy in Nicaragua. In the bottom panel are their closely related replacements in Brazil. Note the scientific names.
What you can do
Study some canopy birds on your own. Visit the website Neotropical Birds by the Cornell Lab of Ornithology. In the Search box type in one of the terms listed below. You will get a photo library, sound recording, range map, and a bio. Neotropical birding from your desktop. I hope that is enough to tempt you to go for the real deal.
Ramphastos – or toucan
Vireolanius – or shrike-vireo
Tangara – or tanager
Thalurania – or woodnymph
Patagioenas – or pigeon
Piaya – or cuckoo
Or just explore on your own and see what you find.
Anderson, D. L. & Naka, L. N. 2011. Comparative structure and organization of canopy bird assemblages in Honduras and Brazil. Condor 113: 7-23.
Naka, L. N. 2004. Structure and organization of canopy bird assemblages in central Amazonia. Auk 121: 88-102.
Photo credits for the bird panels. All photos © as credited.
Nicaragua panel, clockwise from upper left: (toucan) James Adams, (pigeon) Roy Toft, (cuckoo) Nick Athanas, (tanager) James Adams, (woodnymph) James Adams, (shrike-vireo) Dominic Sherony.
Brazil panel, clockwise from upper left: (toucan) Stan Mansfield, (pigeon) Vivek Tawari, (cuckoo) Flávio Mota, (tanager) Sean McCann, (woodnymph) André Andeodato, (shrike-vireo) Anselmo d’Afonsecca.