Darwin’s finches taught us that over time, what a bird eats can shape the size of the bird’s beak. A seminal study conducted by Peter and Rosemary Grant on Daphne in the Galapagos Islands showed that as small and soft seeds were replaced by tougher and larger seeds on Daphne, the average beak size of a Medium Ground-Finch became larger. Over time, bill size evolved to better suit the suite of food items consumed by each species. After all, you need the right tool to do the job.
New research out this week in the journal Proceedings of the Royal Society B shows that the size and shape of a bird’s beak isn’t only shaped only by what it eats.
“If you’re out with your binoculars you can see birds doing all sorts of behaviors with their beaks, things like getting food, building a nest, preening, and singing’” says Nicholas Friedman, lead author of the study from the Okinawa Institute of Science and Technology in Japan. “Since a bird can’t fly around with a Leatherman for a beak, we wanted to know how these competing pressures play out—what determines the shape and size each species’ melted down Leatherman?” says Eliot Miller, co-author and Collections Manager at the Macaulay Library at the Cornell Lab. “Instead of focusing on just one function of the beak, we wanted to compare multiple functions together—things like body size, climate, and how they forage for food. And we wanted to see how these functions change the size and structure of honeyeater beaks, and what impact this evolution has on how they sing,” says Friedman.
Australian honeyeaters are an incredibly diverse group of birds, from the stubby-billed Bell Miner to the large-billed White-streaked Friarbird to the delicately curved-billed Red-headed Myzomela, making them the perfect group of birds to study.
Friedman and colleagues used an existing dataset on the foraging behavior of Australian honeyeaters and scoured museum collections. They measured specimens at the Natural History Museum in Tring, UK and used the audio collections at the Macaulay Library, Xeno Canto, and the Australian National Wildlife Collection – CSIRO to assess song characteristics.
Friedman and colleagues discovered that while the thickness of a bird’s beak was related to how they foraged and what they ate, climate also played a role in shaping honeyeater beaks. Honeyeaters such as the Black-headed Honeyeater that inhabit colder regions of Australia had shorter beaks than their relatives. Factors that shaped the size and structure of a bird’s beak also affected how it sang. For example, species with longer beaks such as Noisy Friarbird sang slower, and species with longer and narrower beaks sang at lower frequencies.
In summary, Friedman and colleagues showed that it’s not just what a bird eats, but how they eat it and where they live that affect both the size and shape of a honeyeater’s beak. And these characteristics, in turn, affect bird song.
I’m reminded of the iconic song by the Rolling Stones, “You can’t always get what you want,” because in nature and in life it’s all about trade-off. Birds are trading-off the benefits that come with having a long bill to consume nectar, for example with reduced capacity to thermoregulate with a long bill.
Because birds are trading off the benefits of one trait in favor of another, the authors argue that birds may be adapting to these trade-offs by changing their behavior. For example, Miller says, “heat-stressed birds with small beaks might modify their activities to search for food primarily at dawn and dusk, or to make frequent visits to the waterhole to cool off.”
This study serves as another reminder that natural history collections including digital sound archives are fundamental for helping us learn more about our world. Thank you, to all of the people who archived their recordings at the Macaulay Library; without you, studies like this would not be possible.
Friedman, N. R., E. T. Miller, J. R. Ball, H. Kasuga, V. Remes, and E. P. Economo (2019). Evolution of a multifunctional trait: shared effects of foraging ecology and thermoregulation on beak morphology, with consequences for song evolution. Proceedings of the Royal Society B 286:20192474 https://royalsocietypublishing.org/doi/10.1098/rspb.2019.2474
This study used recordings by the following Macaulay Library contributors. Thank you for sharing your recordings and being a part of science.
Andersen, Michael J
Beehler, Bruce M
Brown, Eleanor D
Bruner, Phillip L
Class, Alexandra M
Clock, Benjamin M
Freeman, Benjamin G
Greig, Emma I
Heaton Crisologo, Taylor
Kerr, Donald J
Loetscher, Jr., Fred W
Macaulay, Linda R
Mack, Andrew L
Mathers-Winn, Cedar A
McCartt, David A
McNeill, Roger D
Medler, Matthew D
Mittermeier, John C
Orenstein, Ronald I
Pratt, H. Douglas
Pratt, Thane K
Robbins, Mark B
Ward, William V
Zimmerman, Dale A; Edwards, Martin