Here is a bit of good news. Wouldn’t it be amazing to be involved in that research project? If you’re wondering why they can use smelly oil to attract birds, which typically aren’t known for their excellent olfaction, take a look at this. Now, if they could just find an Eskimo Curlew…

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Two species of Antbirds in the Amazon have apparently evolved to use the same song. Using the same song as the other Antbird species allows a male to ‘defend’ its territory using voice alone against two species (rather than just its own species, as most birds would). It’s an interesting phenomenon, as it allows speculation about how natural selection may have created this situation. First, though, you need to know a little about song development in these species.

Antbirds are part of the ‘suboscine’ family of passerines. The Suboscines, or Tyranni, are not song-learners. Most suboscine species are endemic to central and south america, but in North America, flycatchers fall into this category (like Willow, Alder, Pheobes, etc.). They tend to have very simple songs (think of the pee-wees, phee-bee’s, phitz-bew’s, and rising wheeeep’s you hear in the Ontario woods in springtime), which travel more easily and completely through the dense canopies of tropical rainforests than would the more complex songs of many warblers breeding in North America. Interestingly, if these birds are taken from their parents at birth, and never allowed to hear their own species song, they will still develop a very typical song for their own species. It is even more striking, though, that if a suboscine like a Willow Flycatcher is only ever exposed to the song of Alder Flycatchers, it will still only sing the Willow Flycatcher song.

So given the nature of song development in this species, it seems to me that the evolution of two antbirds with similar songs may have looked something like this:
-At some point in their evolutionary history, these two species had different songs.
-Through some genetic mutation, recombination, or other form of natural variation in one of the species, some individuals appeared who sang a song somewhat similar to that of the other species.
-The songs of these individuals fooled the birds of the other species into thinking they had a direct competitor on a nearby territory, and they don’t want to mess with him.
-These mutated individuals, as a result, had fewer birds to chase off their own territory (the non-mutated birds had to physically chase away extra-specific competition, rather than just scare them away with song).
-The mutated individuals had more time to put into finding food for their young, and, as a result, had more young fledge and eventually have their own young.
-Over time, the increased reproductive success of the mutated individuals resulted in a population of antbirds with a very high proportion of ‘mutated’ individuals (at some point, they’re not mutated anymore–they’re normal).

There are a few things to keep in mind here. The same process could have happened simultaneously in both species. This would have made the whole thing happen more quickly, I think (their songs would ‘meet in the middle’). Also, evolution happens in very small steps. It is unlikely that a Peruvian Warbling Antbird who sings a Yellow Breasted Warbling Antbird song was born from a parent who sang an ‘old’ Peruvian Warbling Antbird song. Rather, the songs would have become very gradually more similar over a very long period of time, across many generations of Antbirds. Critically, however, this increased similarity must have resulted in some benefit in reproductive success, even when it was just a very small increase in similarity.

This is mostly speculation, so leave a comment if you speculate differently.

Also, note that a picture of Christine with her new binoculars has been added below.