Data from: How cuckoos find and choose host nests for parasitism

How cuckoos find the nests of their hosts and choose nests with respect to
egg phenotype for parasitism is a long-standing puzzle that has so far not
been solved. We recently developed an experimental design to shed light on
this mystery by studying the egg-laying behavior of common cuckoos
(Cuculus canorus) in nests of its Oriental reed warbler (Acrocephalus
orientalis) host. Our results showed that common cuckoos only parasitized
host nests with host activities but ignored the egg phenotypes in the
nests. Furthermore, cuckoos distinguished between nest types of
black-browed reed warbler (Acrocephalus bistrigiceps) and Oriential reed
warbler and chose to parasitize the latter. This study provides strong
evidence for host activities being a prime factor affecting cuckoo
parasitism. Cuckoos must first locate the general site of host nests from
activities by the host and then target the nests for parasitism. These
observations reject the optimal egg-laying hypothesis stating that cuckoos
are capable of choosing to lay eggs in host nests with visually matching
egg phenotypes. Therefore, our studies challenge the idea that cuckoos
recognize eggs that match their own.