From New Scientist:
Frog embryos listen for bad vibrations to avoid snakes
* 11:33 09 December 2009 by Shanta Barley
To escape being a snake’s lunch, tree frog embryos listen out for bad vibrations.
The jelly-coated eggs of the Central American red-eyed tree frog are laid on vegetation overhanging ponds and can hatch up to three days early if they sense that a snake is approaching. Michael Caldwell at Boston University and colleagues wanted to know how they distinguished between predators and false alarms like torrential rain.
They collected Agalychnis callidryas egg clutches, still on their leaves, from Panama and exposed them to either vibrations at frequencies lower than 100 hertz, which are typical of snake attacks, or rain-like recordings which varied between 0 and 500 hertz. In each case they counted how many eggs hatched early. In a second experiment they played recordings that either started abruptly, like a snake attack, or gained intensity gradually, like rain.
The team found that snake-like vibrations induced the eggs to hatch earlier. They suggest that the embryos can distinguish two characteristics of rain – a pattern of low and high frequency vibrations that increase slowly in amplitude.
Tadpoles prematurely ejected into ponds are poorly equipped to flee fish, says co-author Karen Warkentin, also at Boston University, but this adaptation prevents a snake destroying an entire brood.
Paper on this published here.
Treefrogs converse using vibrations: here.