Many animals produce sounds that identify their species and sexual status. Male songbirds, for instance, are famous for the calls they produce to attract mates. Male frogs and toads also call to attract females. It has been shown that in many frog species, a male’s calls provide clues to his size and health, and that females can identify the largest, healthiest, or least-parasitized males simply by listening to their calls.
Some animal species can even produce flashes of light with which to identify their species and their sexual status. Fireflies are surely the most famous examples of animals that use light to identify themselves and to attract mates.

The Gray Treefrog species Hyla chrysoscelis
(left) and Hyla versicolor
(right). Their geographic ranges
overlap, and both species can be found in the same habitats. They are “cryptic species”; this means
that they cannot be distinguished from each other morphologically. If you find a Gray Treefrog, the only
way to be sure what species you’ve found is through a genetic analysis. Or by listening to its call.
Cryptic species are much more common than most people would guess.

Fireflies use distinctive flashing patterns to indicate their species and attract mates.
The flashing patterns of six different firefly species in the genus Photinus
are shown.