Interference competition is frequently observed in sexually mature adults as they defend breeding territories. However, it remains unclear in many taxa whether juveniles respond aggressively to other juveniles or if they defend resources. To test whether postmetamorphic juveniles of a pond-breeding amphibian were aggressive towards other juveniles or were defending resources, we staged terrestrial encounters between three species of sympatric Ambystoma salamanders. We observed biting and other aggressive behaviors by juvenile Spotted (Ambystoma maculatum) and Marbled Salamanders (Ambystoma opacum). However, we did not observe aggressive behaviors by Ringed Salamanders (Ambystoma annulatum). In addition to species-level variations in aggression, these three species also differed in whether aggression was targeted primarily intra- or interspecifically. This study suggests that juveniles of pond-breeding amphibians of some species may defend essential habitat with agonistic behavior.

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