Effects of age and group size on habitat selection and activity level in Rana pipiens tadpoles

Amphibian larvae may use both intrinsic cues - such as their own age, size or developmental stage - and extrinsic cues - such as chemical cues and gro up size - to make behavioural decisions. We performed a laboratory experime nt to study habitat selection and activity level of Rana pipiens tadpoles a t different ages and in groups of different sizes. Two ages of tadpoles wer e used: early (2 weeks after hatching; Gosner stage 25) and late (8 weeks a fter hatching; Gosner stages 36-38). Three group sizes were used: one, two and six. Tadpoles in pairs or groups tended to be more active and to occur in the open water column more than lone tadpoles. Younger tadpoles tended t o use the open water column less and to be less active than older tadpoles, but there was no effect on the use of the vegetated habitat. Our results i ndicate that the determinants of amphibian larval behaviour include respons es to both intrinsic (body size, age) and extrinsic (group size) cues.