4 o o o o o o o o 4 Passage III recorded. The figure shows, for each group, the average number of offspring (as eggs, as and as Scientists studied how perceived predation (hearing per clutch. the calls and sounds of predators). in the absence of direct NPT group produce 2 clutches (groups) of eggs in a breeding season. Study At the beginning of a breeding season, nests without eggs were located in ow-growing shrubs. 3.6 Direct predation was eliminated by surrounding each shrub with an electric fence to protect the nest from ground predators and by covering each shrub with a net to protect the nest from aerial predators. The nests were evenly divided into 2 groups: a preda 2.4 tor treatment (PT) group and a nonpredator treatment 2.2 (NPT group. A speaker that broadcast the calls and sounds of predators of M. melodia was set up near each nest in the 2.0 first clutch PT group. A speaker that broadcast the calls and sounds of 1.8 nonpredators of M. melodia was set up near each nest in second clutch 1.6 the NPT group 1.2 Throughout the breeding season, each speaker broad- cast the appropriate calls and sounds every few minutes on a 4-day-on, 4-day-off cycle. The parents and offspring associated with each nest did not hear sounds emitted by from Liana Y. zanette et al., \"Perceived Predation speakers other than their own speaker.) The number of eggs Figure adapted offspring Songbirds Produce and the number of hatchlings produced in each nest were Risk Reduces the Number Advancement of recorded. The number of hatchlings that successfully left Year.\" 02011 by American Association for the each nest (such ings are called fledglings) was also Science Solution 14.G. tagging the hatchlings in both groups with identifying markers before they fledged. 15.A 16.H 17.D 18.G 19.A 20.H.