Frogs are small and sometimes have to travel great distances to their breeding ponds. Many of them bypass the ponds with fish in them, for the frogs that try to breed there will not last very long. They may return to the pond where they were transformed from tadpoles, or they will be drawn to another place where they hear the voices of others calling.

The problem is frog fidelity - not to their mates but to their breeding sites, to which they return year after year. The longest migrations are recorded in Eastern Europe, where some frogs travel as far as 15 kilometers (9 miles). It’s difficult to change such deeply programmed directions; common toads have returned to parking lots. Although this is certainly not true for all frogs. Many species visit different locations in a single breeding season.

Many species begin to move when the rains begin or just before in responses to changes in air pressure that signal the rain to come. Depending on where they live, the trigger could be the start of the tropical rainy season, the spring showers and the melting snow of the temperate zone, or the deserts summer thunderstorms. A few species may already be at the pond having spent the winter in saturated muck at the bottom.

The males normally arrive first and set about establishing territories in shallow water. The females wait patiently for the great courtship ritual to begin. Let the songs begin! Now to the uninitiated, this cacophony might seem to be produced by some unmusical chorus of aliens. In the simplest terms however, it is a grand assemblage of males shouting “pick me”. Each version is the product of the frogs vocal cords, greatly augmented by the air sacs in its throat. When the sacs expand in the air, they broadcast the sounds, making the sound call of some species audible kilometers away.

By forcing air into the sacs from the lungs and then from the sacs back into the lungs, frogs use their sacs like bagpipes, allowing them to call continuously, even underwater. A few species that lack the vocal cords still call, however their calls can only be heard a few meters away. The vocalizations provide other frogs that are listening information about the size and health of the caller.
Males near one another commonly call in duets, trios or other small groups. It may be the dominate male of the group who calls first, followed at brief intervals by the males in the chorus. This allows the males to get their message across without being drowned out by the others.

Posted in Reproduction

In most species, the female frog selects the appropriate calling male and the breeding begins. Sometimes the site that the male is calling from is not a good location for laying eggs. However, he will mount the female anyways. She will usually end up carrying him to the proper nesting site.
Nearly all frogs mate by amplexus. This is a technique widely used by fish. The principle is that, if the two sexes are close enough together and plenty of eggs are released into the water at the same time, enough eggs will be fertilized to make the whole thing worthwhile. The male, who is usually smaller, mounts and grips her tightly either in the armpits or just in front of the hind legs.
The pressure from the male griping the female stimulates the female to release her eggs while the male releases his sperm. The two then mix, and fertilize the eggs. Amplexus also prevents other males from dislodging the male. Often though, amplexus is not as reliable as it seems. It appears that the frogs and toads have about as much trouble telling the sexes apart as we do. Male toads in particular will mount anything that resembles a female toad, including dead toads, the wrong species, inanimate objects, and male frogs.

The mounted male toad will then inform the other of his mistake by giving a series of low volume clicks or chuckles. Females also take advantage of this; they will make the call if they are not ready to release their eggs. Amplexus positions vary as well. Males of some species grip the female just in front of the hind legs, others straddle the female. In some species the size difference is so great that the male just leans against the female.

One species of frog takes mating to the extreme. A male harlequin frog defends his territory all year. When a female appears on his turf, he climbs on board and attempts to breed even if the breeding season is many weeks away. The female, as a result, must carry the male around her back for weeks or even months. This is hard on both parties as the female must carry the male around, and the male gets little to eat. Such extreme commitment to amplexus shows that a male has few opportunities to meet females.

Posted in Reproduction