Darwin\u2019s finches helped inspire Darwin\u2019s theory of evolution by natural selection, as their different beak shapes across different Gal\u00e1pagos islands demonstrated how species could adapt to varied food sources over time. Photo of female Darwin\u2019s medium ground finch (Geospiza fortis) courtesy of Andrew Hendry.<\/figcaption><\/figure>\nDespite their historic significance, Darwin\u2019s finches are rather clumsy. \u201cThey\u2019re actually terrible flyers, really poor flyers,\u201d Podos tells Mongabay.<\/p>\n
Still, handling these living pieces of evolutionary history never lost its magic, he says. \u201cThe very first time I caught a Darwin\u2019s finch, I said \u2018You know who you are. You\u2019re famous,’\u201d Podos recalls. \u201c\u2018You may just think you\u2019re a little bird, but you\u2019re a Darwin\u2019s finch.\u2019 And that excitement has never gone away.\u201d<\/p>\n
The study builds on three basic ideas: droughts force birds to develop bigger beaks to crack tough seeds; birds with bigger beaks can\u2019t sing as quickly or with as much variety; and birds use songs to choose their mates.<\/p>\n
These principles were demonstrated during a landmark 1977-78 drought study on Daphne Major Island in the Gal\u00e1pagos, when researchers observed that finches with larger beaks were more likely to survive during severe drought conditions because they could crack the remaining tough seeds.<\/p>\n
\u201cFrom one year to the next, most of the birds died during the drought. The ones that survived had larger beaks, and when they bred, the babies then had larger beaks,\u201d Podos says.<\/p>\n
The changes in beak size were remarkably precise. Each drought event increased beak depth by about 0.49 millimeters. These small changes in beak size have unexpected consequences for how the birds communicate.<\/p>\n
Larger beaks make it harder for birds to produce rapid, complex songs, much like how it would be difficult to \u201cplay the \u2018Flight of the Bumblebee\u2019 on a tuba,\u201d Podos said.<\/p>\n
\u201cIf you have a really huge beak, it\u2019s harder to open and close it really rapidly, and it\u2019s also harder to open it more widely. So that means your song is going to sound different,\u201d Katie Schroeder, a co-author of the study who worked on the research as a Ph.D. student at the University of Massachusetts Amherst, tells Mongabay.<\/p>\n
To understand how these changes might affect species formation, the team created simulated \u201cghost of finches future\u201d songs using sound analysis software. They took recordings of real finch songs and modified them in two ways: inserting tiny spaces between notes to slow down the song\u2019s pace, and using frequency filters to narrow the range of pitches, creating the kinds of changes that would result from larger beak sizes.<\/p>\n
They created versions simulating what songs would sound like after one, three, or six drought events. The six-drought scenario was chosen because it would produce beak changes similar to the actual differences seen between existing species.<\/p>\n
Testing these modified songs required careful experimental design. On the Santa Cruz Island in the Gal\u00e1pagos, researchers carefully captured finches, measured their beaks, then marked them with colored leg bands for future identification before releasing them. The finches, which aren\u2019t migratory, mostly stay in their territories, making them ideal subjects for the playback experiments.<\/p>\n
To test their modified songs, researchers set up speakers in the territories of 12 male finches. Each bird heard four different versions of a song: a normal finch song and three modified versions simulating what that song would sound like after one, three, and six droughts. The team played one version per day, with rest days in between to ensure each bird\u2019s response was fresh.<\/p>\n
Male finches, it turns out, are fiercely territorial during breeding season. When they hear another male\u2019s song, they typically act within seconds, searching for the perceived intruder. \u201cIt\u2019s really fun to do,\u201d Podos says. Some experiments even used taxidermied birds as decoys. When revealed, \u201cThey\u2019ll come in looking for the intruder \u2026 that territory holder will come in and beat the crap out of your mount,\u201d Podos says.<\/p>\nResearchers travel in the Galapagos Islands to tag finches in 2005. Photo courtesy of Bieke Vanhooydonck.<\/figcaption><\/figure>\nWhen hearing normal songs from their own species, males would fly off their perch within about 10 seconds to investigate. The differences were striking and measurable: birds took nearly four times longer to respond to six-drought songs compared to normal ones, and their flight rates decreased by 31%. This suggests they no longer recognized these modified songs as coming from their own species.<\/p>\n
With six-drought songs, \u201cthey pay attention, \u201cPodos says, \u201cbut they don\u2019t leave the perch for about a minute. They\u2019re much more chill about it.\u201d<\/p>\n
They also maintained greater distances from speakers playing the most modified songs. While there were some complications in two trials, excluding these would have actually strengthened these findings.<\/p>\n
\u201cThe study is very well done,\u201d Tim Wright, a biology professor at New Mexico State University who studies bird songs but wasn\u2019t involved in this research, tells Mongabay. \u201c[It] ingeniously projects the effects that successive droughts would have on beak sizes via changes in seed banks, and then simulates the types of songs that could be sung by males with the resulting larger beaks.\u201d<\/p>\nA female Darwin\u2019s medium ground finch (Geospiza fortis) courtesy of Andrew Hendry.<\/figcaption><\/figure>\nPodos also hoped to test female finches, since it\u2019s the females that ultimately choose mates. However, this proved challenging as females are more cautious. \u201cThey skulk around, and they don\u2019t typically approach males,\u201d Podos says. \u201cThey\u2019ll only approach a male if they\u2019re really ready.\u201d<\/p>\n
While many scientists warn that climate change will drive species to extinction, a very real threat, this study suggests that climate pressures might also create new species. When environmental changes force animals to adapt, these adaptations can cascade into differences in behavior and communication that eventually split one species into two. However, the current pace of climate change may be too rapid for many species to adapt through natural selection, which typically occurs over many generations.<\/p>\n
While the study used simulated songs representing six-drought events, both Podos and Wright caution against oversimplification, or concluding that \u201csix droughts makes a new species.\u201d Real climate patterns are complex, with droughts typically alternating with rainy periods. However, Podos says, these patterns may change as the climate crisis continues.<\/p>\n
This article<\/a> by Liz Kimbrough was first published by Mongabay.com on 8 November 2024. Lead Image: A male Darwin\u2019s medium ground finch (Geospiza fortis). Photo courtesy of Andrew Hendry.What you can do<\/h2>\n Help to save wildlife by donating as little as $1 \u2013 It only takes a minute.<\/p>\n