The Striped Cuckoo (Tapera naevia) is an obligate brood parasite with poorly understood breeding habits. Here, we describe the reproductive biology of Striped Cuckoos parasitizing Rufous-fronted Thornbird (Phacellodomus rufifrons) nests in the Cerrado of central Brazil and discuss parasite adaptations. Striped Cuckoos parasitized 38.5% of Rufous-fronted Thornbird nests in October–November. Cuckoos laid 1 white elliptical egg per thornbird nest. The mean mass of eggs was 2.64 g and the mean size was 21.0 × 15.3 mm (n = 4). Striped Cuckoo egg incubation period had a duration of 14.7 ± 1.4 d (n = 7), 2.4 d < eggs of the Rufous-fronted Thornbird (17.1 ± 2.2 d; n = 8). Striped Cuckoo nestlings were very aggressive, pecking their nest mates to death, and the single cuckoo nestling remained alone in parasitized nests for 20.8 ± 1.2 d (n = 8), a duration similar to its host in nonparasitized nests (19.7 ± 1.6 d; n = 14). The mass gain of cuckoo nestlings was faster (3.0 g/d) than thornbird nestlings in nonparasitized nests (1.7 g/d). The predation rate during the nestling stage was similar for nests with a Striped Cuckoo nestling (20%) to that of nonparasitized nests with thornbird nestlings (26%). We propose that several adaptations allow Striped Cuckoos to successfully parasitize Rufous-fronted Thornbird nests: a highly mimetic egg, as the host's egg was also white and elliptically shaped, a smaller egg in proportion to body size, the ability of its nestlings to puncture or eject host eggs and kill host nestlings, a shorter incubation period, a faster nestling mass gain, and a flexible breeding season.

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