(SPARROWS / ANIMAL SCIENCE) As we slog through the late summer months drenched in sweat with our air conditioners cranked up to cool off, some of us may wonder how animals deal with the heat. Without ice makers, fans, and even the ability to sweat, how do our scaly, furry, and feathery friends stay cool?
Ornithologist Russell Greenberg was part of a study that solved two mysteries simultaneously — how do birds stay cool, and why is it that different birds have such a varying array of beaks? Believe it or not, these two questions almost answer each other. Find out how birds use their beaks to stay cool in the sun! — Global Animal
Discovery News, Amy Enchelmeyer
Bird beaks may help them beat the heat, according to new research on salt marsh sparrows.
Smithsonian scientists studied five different species of salt marsh sparrows across North America, all living in similar tidal marshes, and found the bill sizes of the birds varied drastically depending on the average summer temperature — sometimes up to a 90 percent difference.
The research suggests that beaks are not simply for eating and foraging, even though it has appeared that way to science since Charles Darwin’s famous finches.
“Bird bills are known to be evolutionary in development,” said Russell Greenberg, head of the Migratory Bird Center at the National Zoo and co-author of the study. “But it’s usually in a diet or niche overlap way that’s so dominate you don’t really think of it as being anything else.”
Greenberg has been studying salt marsh sparrows for more than a decade, noting how the birds manage to survive and adapt to the extremely harsh conditions of a tidal marsh. The study measured the beaks of 1,380 birds. And while all the birds ate the same things and lived in similar habitats they weren’t the same.
“Rather than focusing on their similarities, I started focusing on their differences,” said Greenberg.
One major difference was in beak size, even though all the birds lived in the same ecosystem.
Salt marsh sparrows — a name given to any sparrow species living in tidal marshes — lead a tough life because of their surroundings. The grassy nature of marshes leaves little overhead protection or trees in which to seek shade or nest. Their water sources are briny. And the constant ebb and flow of the tide makes nesting in the ground especially problematic. They feed on whatever they find — an array of insects, grasses and even the swamp-loving arthropods.
“It’s a physiologically challenging environment,” Greenberg said.
So Greenberg and his fellow researchers took their cues from previous studies that showed the famously-beaked toucan has an active vascular system, or blood flow, to its bill that change as regularly as, well, the weather.
“They’re [the toucans] actively using the bill by restricting or adding blood to it,” he explained. “It’s very active tissue.”
Greenberg’s study on salt marsh sparrows suggests this beak tissue may be active in order to transfer heat and keep a bird cool in such a harsh environment.
Birds don’t sweat in the same way humans do. When they begin to overheat, they don’t have many options. They can find shade to try to cool off or try to not expend too much energy. But ultimately, hot birds can’t do much but pant. Increased panting can help reduce their overheating but it also brings on water loss, which then can dehydrate the bird.
Greenberg believes that being able to transfer heat to a beak — the bigger the beak, the more heat it can take —could be an evolutionary tactic to stay cool and prevent dehydration.
It makes sense given other animals’ thermoregulation tactics. Desert hares have long ears that act as a way to expel excess heat. A turkey’s wattle has been shown to have a similar purpose.
It’s a matter of extremes and extremities. When things get hot, animals have to find a way to cope with the excess heat; the more surface area, the more heat can be dispensed.
In colder temperatures, animals benefit from shorter limbs and less surface area to keep warm. This is known as “Allen’s Rule,” named for Joel Asaph Allen who first proposed the theory in 1877.
And while it might seem simple enough jump to birds and beaks, it throws a proverbial wrench in what science generally assumed about beaks since Charles Darwin’s finches — that a birds’ bill size and shape is influenced by what it eats.
The salt marsh sparrows are considered to be “generalists” — meaning they’ll eat whatever they can, so beak size isn’t necessarily completely dependent on their food. Regardless, Greenberg thinks the two theories can coexist.
“This isn’t intended to be a universal theory. But we have to think of it as a lot more going on with bills than processing food — it [thermoregulation] may be one of the most important things going on sometimes.”
Greenberg’s team is currently analyzing thermographic images of bird’s beaks and legs to get a better idea of how, and when, the flow of heat to the extremities begins.