Strategy of landing behavior of the tree frog Hyla japonica.

Abstract

Toads on the ground control landing behavior by a simple strategy in which they extend their elbows at roughly the same time after take-off and continue extending them at the same velocity until they land. However, this simple strategy does not work well in much more complicated arboreal habitat. We analyzed properties of jumping and timing of forelimb extension of the tree frog, Hyla japonica, to demonstrate how the arboreal species land safely. The results showed that distance, duration, and velocity of jump were not affected by explicit optic flow information, whereas the all three parameters decreased significantly in the blindfolded animals. This suggests that the frogs do not use optic flow information during flight but need visual information to plan a jump to reach the destination appropriately. Many animals generate prelanding behavior when time-to-contact reaches a threshold value. However, the results showed that a significant positive correlation was found between jump duration and time-to-contact both in normal and blindfolded animals. The slopes and the intercepts of the linear regression lines were about 0.8 and about 50msec, respectively, in both cases. These suggest that, without any visual inputs, the animal can make the decision for prelanding forelimb extension at 20% of jump duration and start extending the forelimb after a motor delay of about 50msec as in the normal condition. This strategy enables the tree frog to always maintain 80% of the jump duration to prepare for landing in their complex habitat.