Interspecific plumage mimicry in toucans

Mimicry among co-existing toucans: White-throated and Channel-billed Toucans live together in the Amazon and look the same. Chestnut-mandibled and Choco Toucans live together in the lowlands west of the Andes and look the same. Nevertheless, the Chestnut-mandibled Toucan's closest relative is the very dissimilar White-throated Toucan, and the Choco Toucan's closest relative is the very dissimilar Channel-billed Toucan. Modified from Ridgely and Greenfield's Aves del Ecuador.

Mimicry among co-occurring toucans: White-throated and Channel-billed Toucans live together in the Amazon and look the same. Chestnut-mandibled and Choco Toucans live together in the lowlands west of the Andes and look the same. Nevertheless, the Chestnut-mandibled Toucan’s closest relative is the very dissimilar White-throated Toucan, and the Choco Toucan’s closest relative is the very dissimilar Channel-billed Toucan. Modified from Ridgely and Greenfield’s Aves del Ecuador.

Evolutionary biologist Jerry Coyne (author of Why Evolution is True and coauthor of Speciation) kindly posted my photos of the Plate-billed Mountain-Toucan  (Andigena laminirostris) on his website today. Earlier today I wrote a post about the striking similarity of color patterns in the Plate-billed Mountain-Toucan  and the Toucan-Barbet (Semnornis ramphastinus), and  I mentioned this mimicry in the comments on Jerry’s site. Reader Bruce Lyon responded to my comment by reminding me that there are other remarkable examples of plumage mimicry among the toucans.

Co-existing Amazonian toucans: Left, Channel-billed Toucan (a croaker); right, White-throated Toucan (a yelper. Photos from Roger Ahlman.

Co-occurring Amazonian toucans: Left, Channel-billed Toucan, a croaker; right, White-throated Toucan, a yelper. Photos from Roger Ahlman.

For example, here in the lowlands of Amazonian Ecuador two large Ramphastos toucans co-occur, the White-throated Toucan (Ramphastos tucanus) and the Channel-billed Toucan (R. vitellinus). They have very different songs: the larger White-throated Toucan is a “yelper” while the slightly smaller Channel-billed Toucan is a “croaker”. However, both species have virtually identical plumages. If they are not singing it can be very difficult to tell them apart, except by the bill proportions (the Channel-billed Toucan has a smaller bill relative to its head).

Co-existing  Choco lowland toucans: Left, Chestnut-mandibled Toucan, a yelper; right, Choco Toucan, a croaker. Photos from Roger Ahlman.

Co-occurring Choco lowland toucans: Left, Chestnut-mandibled Toucan, a yelper; right, Choco Toucan, a croaker. Photos from Roger Ahlman.

On the other side of the Andes, in the western Choco lowlands, there is another pair of co-occurring Ramphastos toucans: a “yelper”, the Chestnut-mandibled Toucan (R. swainsonii), and a slightly smaller “croaker” Choco Toucan (R. brevis). These also have plumages that are identical to each other, but they are completely different from the plumages of the Channel-billed and White-throated Toucans on the other side of the Andes.

Judging only by their appearances, anyone would think that the identical-looking Chestnut-mandibled and Choco Toucans of the western  lowlands were each other’s closest relatives. Anyone would also think that the White-throated and Channel-billed Toucans of the eastern (i.e Amazonian) lowlands were also each other’s closest relatives, since they are almost identical to each other and very different-looking from the western pair of toucans.

However, bill shape and song link the big western species to the big eastern species, and the smaller western species to the smaller eastern species, in spite of their very different colors. DNA analysis (Weckstein 2005) conclusively proves that bill shape and song, not the birds’ colors, are the phylogenetically informative characters in this case. (One of the most exciting things about DNA analysis is that it teaches taxonomists which morphological characters indicate evolutionary history.) The croakers on each side of the Andes are each other’s closest relatives, and the yelpers on each side of the Andes are each other’s closest relatives. This means the nearly perfect match between plumages of the coexisting species has come about through natural selection rather than inheritance from a common ancestor. There must be a very strong survival advantage to looking as they do, for one or both coexisting species.

Ramphastos toucan phylogeny, from Weckestein (2005), with toucan heads from Ridgely and Greenfield, Aves de Ecuador.

Ramphastos toucan phylogeny, from Weckestein (2005), with toucan heads from Ridgely and Greenfield, Aves de Ecuador.

What could the advantage be? One possibility, proposed especially by Prum (2014), is to reduce interspecific social dominance interactions. If larger toucans drive away smaller species of toucans feeding in the same tree, then it is advantageous for the smaller species to resemble the larger species. This might defuse the larger species’ instinctive aggression against non-conspecifics. An alternative theory relies on the observation that toucans are nest raiders. Most birds fear the largest toucans and do not put up a fight when they raid a nest. Perhaps if the smaller toucan looks like the larger and more fearsome species, other birds will mistake the smaller species for the larger one and flee more often.

Note added July 25: It remains possible that both species in each region have evolved these colors because they are regionally advantageous to both species. However, it is difficult to imagine what regional selective pressures, other than pressure for mimicry, would make the two co-occurring species so precisely similar to each other in each region. In the comments on my last post, in response to a question by Peter Tobias, I suggest some experimental tests of the mimicry hypothesis. End of note.

This kind of near-perfect apparent mimicry is rather rare in birds. It is probably facilitated in this case by the genetic similarity of the species involved. A pattern that is easy to evolve in one member of the pair should also be easy to evolve in the other member of the pair, since their genetic architectures are so similar. Perfection would be harder to achieve in more distantly-related mimicry pairs, like the Plate-billed Mountain-Toucan / Toucan-Barbet pair I wrote about in the previous post.

The Toucan-Barbet (left, photo by Roger Ahlman) and the Plate-billed Mountain-Toucan (right, photo by Lou Jost) occur in the same forests and have  similar plumage colors and patterns.

The Toucan-Barbet (left, photo by Roger Ahlman) and the Plate-billed Mountain-Toucan (right, photo by Lou Jost) occur in the same forests and have similar plumage colors and patterns.

There are other apparent cases of mimicry in Neotropical birds. The Kiskadee-like flycatchers, those nemeses of beginner birdwatchers, are possible examples. However, it can be hard to separate phylogenetic constraints (inherited genetic architecture) from actual mimicry. The toucan case seems nearly ironclad, now that we know their phylogeny. Now that we know are pretty sure mimicry happens in birds, we should be on the lookout for other examples, and I think the Toucan-Barbet case I mentioned in my last post is best interpreted this way.

Prum, R. (2014) Interspecific social dominance mimicry in birds. Zoological J of the Linnean Society 172: 910-941.

Weckstein, J. (2005) Molecular Phylogenetics of the Ramphastos Toucans: Implications for the Evolution of Morphology, Vocalizations, and Coloration.The Auk 122: 1191-1209.

Lou Jost (www.loujost.com)

Plate-billed Mountain-Toucan, Andigena laminirostris

Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photo: Lou Jost/EcoMinga.

Click to enlarge. Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photo: Lou Jost/EcoMinga.

Here’s a wildlife interlude between Part 3 and Part 4 of my endemic orchid talk. I have just returned from a visit to our Dracula Reserve with Dr Robert Ridgely (author of Field Guide to the Birds of Ecuador, Birds of Panama, Birds of South America, etc, and director of the Rainforest Trust, one of the major donors for the Dracula Reserve), Nigel Simpson (a director of Fundacion EcoMinga, and also of the World Land Trust and Fundacion Jocotoco), Javier Robayo (Exec. Director of Fundacion EcoMinga), David Agro (a director of the Fundacion Jocotoco), Francisco Sornozo (Conservation Director of Fundacion Jocotoco), Heinz Schneider (Curator, University of Basel Botanical Garden, another major donor for the Dracula Reserve), Rafaella Schneider (professor, University of Basel), and Hector Yela (EcoMinga warden). The trip was wonderful, a nice mix of birds and plants, and later I will post some of the things we saw. But I can’t wait to post our photos of this amazing Plate-billed Mountain-Toucan (Andigena laminirostris), one of the most beautiful birds in the world. This species is restricted to mid-elevation Choco cloud forests in the western Andes of Colombia and Ecuador. Learn more about it here.

Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photo: Francisco Sornozo.

Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photo: Francisco Sornozo.

This toucan is quite common in our Dracula Reserve, and we saw and heard and photographed them several times on the first day of our trip. At the end of that long day of birdwatching and botanizing, some of us were driving down the mountain to our hotel, when I spotted this toucan in the roadside trees. It flew across the road in front of our car and sat in good view in a bare branch. We pulled alongside and watched enraptured as it preened, regurgitated seeds, and modeled for us in the soft evening light. We took hundreds of pictures and many videos of it. Francisco, who is one of Ecuador’s most experienced ornithologists, was so moved as he was filming and photographing it that he said this was the most perfect and most beautiful bird observation he had ever experienced in his whole life. Here is a clip of one of the videos I made of it that evening. I cut out some random conversation, but Francisco made his nice comment near the end, and I left it in the clip. Then Bob Ridgely translates for the non-Spanish-speakers in the car.

Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photos: Lou Jost/EcoMinga.

Click to enlarge. Plate-billed Mountain-Toucan, Andigena laminirostris, near our Dracula Reserve. Photos: Lou Jost/EcoMinga.

Plate-billed Mountain-Toucan, Andigena laminirostris, preening near our Dracula Reserve. Photo: Lou Jost/EcoMinga.

Click to enlarge. Plate-billed Mountain-Toucan, Andigena laminirostris, preening near our Dracula Reserve. Photo: Lou Jost/EcoMinga.

We have two other mountain-toucans in our reserves. The Gray-breasted Mountain-Toucan (Andigena hypoglauca) lives in our Cerro Candelaria, Rio Verde, Chamana, Rio Valencia, and possibly our Zunac reserves, while the Black-billed Mountain-Toucan (Andigena nigrirostris) occurs in our Zunac, Cerro Candelaria, Naturetrek, and possibly our Rio Verde reserves. See our video of the Gray-breasted Mountain-Toucan here.

Gray-breasted Mountain-Toucan (Andigena hypoglauca). Painting by Lou Jost.

Gray-breasted Mountain-Toucan (Andigena hypoglauca). Painting by Lou Jost.

Gray-breasted Mountain-Toucan (Andigena hypoglauca). Photo: Roger Ahlman.

Gray-breasted Mountain-Toucan (Andigena hypoglauca). Photo: Roger Ahlman.

Black-billed Mountain-Toucan (Andigena nigrirostris). Photo: Roger Ahlman.

Black-billed Mountain-Toucan (Andigena nigrirostris). Photo: Roger Ahlman.

There is one other mountain-toucan, the Hooded Mountain-Toucan (Andigena cucullata), native to Bolivia and Peru.

Note added July 25: This bird’s plumage may be imitated by the Toucan-Barbet (Semnornis ramphastinus); see my recent posts on plumage mimicry here (Toucan-Barbet) and here (more toucans).

Lou Jost
www.loujost.com

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Gray-breasted Mountain-Toucan (Andigena hypoglauca)


The four species of Andigena toucans are some of the most dramatic birds of middle and high elevation cloud forests in South America. We have two species in our reserves, the Black-billed Mountain-Toucan (Andigena nigrirostris) and the one featured in this video, the Gray-breasted Mountain-Toucan (Andigena hypoglauca). The Gray-breasted Mountain-Toucan lives at very high elevations, from about 2400m all the way up to timberline. It mostly eats fruit, but may also use its long beak to reach into other birds’ nest holes and gobble their chicks.

The video was taken by Manuel Chapungal (a resident of the area, and volunteer caretaker of this mountain) near our seventh and newest reserve, a 15 ha forest bought through a donation by my friend and colleague Anne Chao. This reserve is adjacent to the 100 ha Chamana Reserve, owned by Juan Pablo Reyes, whom we have hired as manager of EcoMinga’s reserve system. The mountain valley protected by these two reserves is very beautiful though partly deforested due to past cattle ranching. It still hosts Mountain Tapir, Spectacled Bear, wild cats, and many many birds.

Our Chamana reserve is in the leftmost patch of sunlight. Click to enlarge. Photo Lou Jost/EcoMinga.

Our Chamana reserve is in the leftmost patch of sunlight. Click to enlarge. Photo Lou Jost/EcoMinga.

This forest gets a lot of hunting pressure due to its nearness to the town of Banos. One day Juan Pablo’s sister was in that area alone, checking her automatic cameras for her study of tapirs, when she ran into two illegal sport hunters with shotguns. She was afraid but slipped away and called Juan Pablo on her cell phone. Juan Pablo, his family, and Manuel Chapungal climbed the mountain and found the hunters. Though Juan’s group was unarmed, they somehow managed to disarm the hunters, confiscating their guns and the bird they had shot. That’s one reason why Juan Pablo is our reserve manager!

Guns and dead guan confiscated  in Chamana by Juan Pablo Reyes, family, and friends. Juan Pablo is at far right, Manuel (who made the toucan video) at far left.

Guns and dead guan confiscated in Chamana by Juan Pablo Reyes, family, and friends. Juan Pablo is at far right, Manuel (who made the toucan video) at far left.

Thanks to Anne Chao for her support for this, to Manuel for sharing his video, and to IdeaWild for donating the video camera to Manuel via the Fundacion Oscar Efren Reyes.

Lou Jost