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This savannah sparrow doesn't have to sweat it-he's got a big beak! Credit: Cephas
      
Beaks come in all shapes and sizes. From the egret’s elegantly tapered, skewer-like dagger to the vulture’s curved, razor-sharp shredder, bird beaks all serve a distinct purpose in nature. Until now, scientists have generally assumed that beak structure developed according to food needs—the egret can stab a darting fish, the vulture can rip flesh from carrion. But new research reveals these elegant structures can serve an additional need: temperature control.
     
In the flat, expansive salt marshes that line many coasts around the U.S., shade is often hard to come by. Especially in the south where summer temperatures regularly break 100 degrees, salt marsh dwellers like sparrows must find ways to avoid roasting.
     
Researchers from the Smithsonian Migratory Bird Center studied 1,380 tidal salt marsh sparrows of ten species and subspecies around the country to see how they cope with the heat. The birds hailed from California, the northeast, and the southern coasts. Their salt marsh habitats sported similar conditions with one exception, the temperature.
    

Song sparrows also use the beak temperature control trick. Credit: Cephas
  
Temperature turned out to clearly influence the size of the birds’ beaks, explaining about 85 percent of the variance, according to published in Ecography. The higher the daily temperature birds had to contend with, the larger the accompanying beak. Some of the sparrows had beaks up to 90 percent larger than their same-species counterparts living in cooler marshes.
     
According to the researchers, large beaks encourage the animals to “dump heat” while conserving moisture (birds don’t sweat). Pumping blood into the beak’s tissue allows birds to release body heat. The larger the surface area of the beak, the more efficient it is for thermoregulation.
      
This discovery fits in nicely with a scientific theory called Allen’s Rule. The theory predicts that warm-blooded animals in hotter climates will have longer appendages than those in colder climates. Blood flow is increased to poorly insulated extremities like a rabbit’s ears or a turkey’s wattle, and as a result helps the animal to cool down. And now biologists can add salt marsh sparrow beaks to the example list of Allen’s Rule.

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