Male birds increased their territorial behavior and female birds approached the loudspeaker at a much higher rate when a local song was played than when the other population’s song was played. Moreover, when the eastern songs were played to finches on the west coast (and vice versa), the birds responded much more strongly to songs from their own side of the island. They found significant differences between the two groups in song duration, syllable rate, and peak frequency. ![]() They recorded the songs of 20 male mangrove finches on the western population, and the songs of the only 2 males they could locate in the eastern population. ![]() The authors decided to test whether this isolation has caused enough divergence between the two populations that they are unlikely to interbreed. The two populations are separated by more than 40 miles of lava desert and volcanic terrain, and the authors estimate that they have been isolated from each other for more than 100 years. ![]() Only two populations survive: one group of about 80 birds on the island’s west coast, and a tiny population of about 20 on the island’s eastern side. There are only about 100 mangrove finches in the world, and they are all confined to Isabela, one of the Galapagos islands. Darwin’s finches may be the best-known example of evolution by natural selection, yet a new study suggests that one species of this famous group of birds may be reaching an "evolutionary dead end." According to a paper in PLoS ONE this week, the mangrove finch-one of the rarest birds in the world-is undergoing a speciation event that could reduce it to two populations with dangerously small numbers.
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