Learning about predators in the egg
Even before they have hatched from the egg, frogs can learn which predators will hunt on them. Earlier it was discovered that amphibians and fish can make this distinction in the larval stage, but now this has also been observed in the embryonic stage.
A team of Canadian and American researchers investigated this. Water in which a predatory salamander and injured tadpoles had swum was poured into a tub with frogspawn from a wood frog. This was done at different points in time, with different amounts of injured tadpoles. By comparing the amounts of injured tadpoles the embryonic frogs could learn when salamanders are most dangerous.
Once the tadpoles hatched from their eggs, their reaction to water with salamander traces was measured. The tadpoles that had been very active before now laid still for minutes. This reaction was the most intensive at time points when many injured tadpoles had been detected.
The results of this study were published in the scientific journal Behavioral Ecology and Sociobiology.