It turns out that to tell the sex of a Galápagos penguin, all you need is a ruler.
In a paper published April 5 in the journal Endangered Species Research, scientists at the University of Washington announced that, for a Galápagos penguin, beak size is nearly a perfect indicator of whether a bird is male or female. Armed with this knowledge, researchers could determine the sex of a bird quickly and accurately in the wild without taking a blood sample — speeding up field studies of this unusual and endangered seabird.