Size matters to tree frogs

August 24, 2010 at 02:07 PM

For female red-eyed tree frogs, size does seem to matter—and the mating call of the male tells them everything they need to know. A study of the mating calls of male Morelett’s tree frogs in Belize found that larger frogs more readily find a mate. The rate, frequency, and duration of the male’s calls carry this vital information to the listening females.

The study appears in the September 2010 issue of the journal Herpetologica. The author recorded 575 mating calls from 30 male tree frogs in the Cayo District of Belize. The frogs exhibited their own unique identities; that is, more differences in calls were found from one frog to the next while an individual frog’s calls did not vary greatly.

Shortly after sunset, male frogs descend from the forest canopy to sound their choruses. The advertising “zworp” call is used to attract females while the more aggressive “chuckling” calls are used among other males.

Among these frogs, it is predominantly female choice—rather than competition among males—that determines mating partners. The energy-consuming call that a male frog of large body size is able to emit seems to speak to the women of this species.

The laryngeal apparatus of a larger frog has greater mass, allowing a lower dominant frequency of its call. Its calls are also longer and more frequent. These are clear signals to females of a male’s size and therefore quality as a mating partner. Large size reflects a frog’s abilities to survive, feed, grow, and outcompete with other males.