Fig. 1

The change in heart rate (HR) (mean ± SE beats / minute) in Superb Fairy-wren embryos exposed to 18 different incubation calls of the same fairy-wren (filled circle; habituation trial) and 6 different incubation calls of a novel fairy-wren (hollow circle; dishabituation trial). Initially, embryos lowered HR during exposure to incubation calls every 10 s from 10 to 60 s (filled circles, H1 phase), lowered HR after renewed exposure to calls of the same female every 10 s from 120 to 180 s (filled circles, H2 phase), and then ceased to lower HR during renewed exposure to calls of the same female every 10 s from 240 to 300 s (filled circles, H3 phase). When embryos were exposed to calls of a novel female every 10 s from 360 to 420 s, they again lowered their HR (hollow circles, D phase)