Which major threat leads to low fledging success rates in the native range?

Answer

Brood parasitism by cuckoos

A significant biological challenge is brood parasitism, primarily by the Lesser Cuckoo. The bush warbler typically fails to eject the parasitic egg, leading to breeding failure, especially when the cuckoo lays its egg later in the season.

Which major threat leads to low fledging success rates in the native range?
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