observations that recently metamorphosed oregon spotted frogs (Rana pretiosa) appear to allow close approach before fleeing led us to contrast their flight initiation distances with those of introduced American Bullfrogs (Lithobates catesbeianus) in order to determine whether this anti-predator variable had the potential to make R. pretiosa vulnerable to predation. using a rangefinder radio-linked to a high-resolution global positioning system unit, we quantified flight initiation distance for recently metamorphosed juveniles of both species using a controlled approach at Conboy lake national wildlife refuge, Washington state, USA. recently metamorphosed R. pretiosa typically allowed extremely close approach (median flight initiation distance, =0.07 m, range: 0-6.5 m) with over 30% of frogs approached allowing themselves to be touched prior to fleeing. in contrast, recently metamorphosed L. catesbeianus typically did not allow close approach, always fleeing at distances 3 1.7 m (flight initiation distance, =6.1 m, range: 1.7-13.9 m). the close approach tactic of R. pretiosa would be consistent with a crypsis-based anti-predator strategy; whereas, L. catesbeianus uses a flight-oriented method of avoiding predation. permitting close approach may place recently metamorphosed R. pretiosa within the typical predatory strike range of L. catesbeianus, which may explain the disappearance of R. pretiosa in areas invaded by L. catesbeianus. Rana pretiosa at Conboy lake represents a unique instance of long-term co-occurrence with L. catesbeianus, raising questions about the basis of this co-occurrence.
