Convergent Defensive Behavior of Two Leaf-Litter Frogs of Southeastern Brazil

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Abstract
The microhylid Stereocyclops parkeri and the leptodactyloid Proceratophrys appendiculata are terrestrial frogs of the coastal rainforest in southeastern Brazil, living in the litter accumulated on the floor and spending most of the time half-buried among fallen leaves. A defensive behavior which enhanced their resemblances to fallen leaves was observed. When the leaf-litter in the immediate vicinity is disturbed, the frog makes a short leap, landing with its legs stretched backwards and remains remarkably still. It may be touched without its changing the posture, keeping the legs stiff and body flat. Placed with its belly up, the frog turns with an almost imperceptible movement of 1 arm and resumes its leaf like posture. The immobility may last as long as 30 min if there is some activity nearby but on some occasions the frog may move forwards a little with a quick movement of the feet, this displacement resembling that of a flicked leaf. The cryptic appearance combined with such a characteristic behavioral pattern may protect against visually oriented, litter-disturbing avian or other predators. Some litter-foraging birds are known to eat such forest-floor frogs as Brachycephalus ephippium, a small, bright-yellow species. A frog which appears and behaves as a casually dislodged leaf may alert little interest in such a predator, as well as in some visually oriented snakes or mammals. The similarity of this defensive behavior among representatives of 2 unrelated frog groups strongly suggests behavioral convergence, possibly due to similar predatory pressures on the forest floor. A similar but less well-developed behavior was observed in another leaf-litter frog, Zachaenus parvulus, in which the legs are not as stretched as in the preceding 2 species and the immobility period is considerably shorter.

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