Warmer World, Bigger Beaks

One advantage of having a beak: built-in air conditioning. Among the many crucial functions a beak serves, it allows some birds to control their internal temperature without having to sweat—a massive advantage for species in hot, humid climates. In 2009, Glenn Tattersall, a professor of zoology at Canada’s Brock University, published a study that used thermal imaging to show that by pumping blood through their large beaks, toucans can shed as much as 60 percent of their body heat.

Soon after his paper was released, Tattersall went to Australia. There he started chatting with Matthew Symonds, an ecologist at Deakin University, about his toucan work in relation to Allen’s Rule, an ecological tenet which states that the body sizes and shapes of endotherms (warm-blooded animals) correspond to temperature. More specifically, Allen’s Rule posits that species living in cold climates will have smaller and more compact appendages than animals in warm climates.

Since that initial conversation, the two scientists have been intent on figuring out whether Allen’s Rule has any bearing on a bird’s beak size. In 2010, the pair published a collaborative paper comparing the size of a massive range of species’ beaks, from parrots to penguins, while controlling for variables like what kind of food the species eats or nuances in habitat. Their findings were consistent with Allen’s Rule: Birds at higher—and thus cooler—altitudes and latitudes tended to have smaller beaks than those in warmer climates.

This confirmation led Symonds to broach to another question: How is this trend being impacted by climate change? In other words, are beaks getting bigger in response to the warming climate?

In March, Symonds published a paper in the Journal of Biogeography showing that between 1871 and 2008, as temperatures in Australia rose, the beaks of four out of five species of native parrots grew larger. Symonds spoke to Audubon about his findings and how climate change might be altering the playing field for birds.

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Why did you choose to look at native Australian parrots for your latest study?

Some of the species—the Mulga Parrot, Gang-gang Cockatoo, Red-rumped Parrot, Australian King Parrot and Crimson Rosell—we covered in the 2010 study, so the link between beak size and temperature was already established. We also wanted species easy to sex to rule out sexual dimorphism [significant differences in size between males and females] as a variable.

We used parrots that were common in our museums, as we were relying on bird skins. One of my honors students, Daniel Campbell-Tennant, measured the beak size, plus things like the wing and leg length, of 410 skins spanning from 1871 to 2008.

And what did you find?

All but the king parrot displayed the predicted outcome: about a 4–10 percent increase in beak surface area. As a whole, Australia has had a 0.8 degree Celsius [1.44 degree Farenheit] increase in the last century, and 0.6 degrees Celsius [1.08 degree Farenheit] rise since 1950. So we split the beak measurements by this defining period and found that they began to increase much more drastically after 1950.

Before Tattersall’s work, beak evolution was mostly supposed to be dependent on factors like diet, sexual selection and vocalization. But our findings show that the need to thermoregulate does play a role in beak evolution.

Will changing beak sizes pose challenges for birds, or are they largely beneficial?

The first thing I like to think about is that this is evidence birds may be adapting to climate change, actually in the process of responding this entire time. There could be reason to worry if changes interfere with diet or life habits, but there are clear survival benefits to these alterations, or birds wouldn’t adopt them. Whatever the driving forces behind the trend, research now needs to focus on the consequences of a process already in play.

What’s left to prove?

We can’t conclusively nail down that temperature increase is the sole factor behind beak size, since we haven’t ruled out other deviations a warmer climate brings. The indirect effects of climate change, like altered seed availability or drier conditions, could turn out to be driving beak evolution as well. Passing the question by other species, in a similar way to what we did in this study, is the next step. It’s most likely that all types of birds will show similar patterns of change as these Australian parrots did, and if they do we can interpret more conclusively what’s happening on a larger, broader scale. 

Correction: 0.8 degrees Celsius is equivalent to 1.44 degrees Farenheit, and 0.6 degrees Celsius is equivalant to 1.08 degrees Farhenheit.