Sensory Mediation of Aggregation among Postmetamorphic Bufo cognatus

Quantification of toad spatial distributions confirmed that postmetamorphic Bufo cognatus form aggregations under natural conditions in southeastern South Dakota. Distributions of toads in symmetric arenas placed in the field indicated that asymmetrical distribution of habitat features, and resulting mutual attraction to resources, is not required for aggregation formation in postmetamorphic toads. Rather, these data suggest that toadlets are attracted to conspecifics. In a similar laboratory experiment, aggregations occurred under light, but not dark, conditions suggesting a role for vision in mediation of this behavior. Additionally, toads were attracted to areas that had been occupied previously by postmetamorphic conspecifics, suggesting that orientation to chemical cues is involved in the aggregation response. This is the first demonstration of attraction to conspecific chemical cues in nonlarval anurans. Field observations of defensive behavior of grouped and solitary postmetamorphic toads supports the hypothesis that aggregation may be an anti-predator strategy of this species.