Fixed interval performance in turtle doves: A comparison with pigeons and rats

Turtle doves, pigeons and rats were trained on fixed-interval (FI) 2, 4, 6, 8- and 110-mi, schedules. Response rates were at each FI value, higher in both bird psecies. They decreased as FI value increased in rats and pigeons. Rat's curvature indices were in all cases superior to those of birds, and the turtle dove differed significantly from pigeons at 2, 4 and 6 min. Curvature indices decreased in rats and increased in birds (except for 2 turtle doves) as the FI value increased. These results question the traditionally assumed cross-species generality of performance in FI schedules.