We studied breeding behavior and size-related variation in advertisement calls of the Plains (Scaphiopus bombifrons), Couch's (S. couchi) and New Mexico (S. multiplicatus) spadefoot toads in southern Arizona during July and August, 1980-83. No call variables (frequency, pulse rate or duration) were correlated with male snout-vent length in S. bombifrons or S. couchi. However, dominant frequency was significantly correlated (negatively) with male size in S. multiplicatus. Males in amplexus were not significantly larger than non-mating males in three of three S. couchi or three of three S. multiplicatus breeding aggregations. Non-calling, actively searching males were observed in aggregations of S. couchi and S. multiplicatus, and in S. multiplicatus actively searching males were significantly smaller than calling males.
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