the Horsfield's bronze cuckoo does not build its own nest but will use a host species' nest to lay its eggs. The breeding season for the Horsfield's bronze cuckoo relies on their host and they will lay one to mimic that of the fairy wren or thornbill's egg, an elongated pinkish-white egg, that is speckled with red-brown spots. The breeding season for the superb fairy-wren is between September and February and a female may have three consecutive broods in this time, allowing the cuckoo multiple attempts to parasitise this species. The female cuckoo may choose a breeding site with a high density of hosts, which allows extra opportunity for her success in parasitising a nest successfully. Studies have shown at one site a female did not parasitise a territory with less than 23 breeding pairs of their primary host (Malurus cyaneus). The egg of a Horsfield's bronze cuckoo is small for its size, evolving over time to mimic those of their host in what can be described as an evolutionary arms race between parasite and host. Also, the smaller the host for the cuckoo, the likelihood of successfully raising multiple broods thus the energy and nutrients needed to produce more smaller eggs than few larger eggs can be utilised more efficiently. Egg laying is very fast for the Horsfield's bronze cuckoo; it is able to lay an egg in under 6 seconds typically in the morning shortly after the host has laid. The adult cuckoo removes one egg each time she lays, only laying one egg per nest and replacing one host egg with one of her own. Younger, semi-experienced females were generally selected over new and novice breeding females due to their success and experience. The Horsfield's bronze cuckoo chose females that would choose similar breeding sites to previous years and were likely to raise several broods in one season. Generally, the superb fairy wren will not reject the cuckoo's egg. Fairy-wrens make oval dome nests that can be dark inside, meaning it is harder for the fairy-wren to distinguish between its own egg and the host's egg. Furthermore, the mimicry in eggs from the Horsfield's bronze cuckoo has evolved over time and the parasite eggs are hard to distinguish except for their slight elongation and glossier finish. The cuckoo chick hatches within 12 days of incubation, 2 days before the host egg, ejecting other eggs in the nests