Evidence for egg discrimination preceding failed rejection attempts in a small cuckoo host

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Ornithology

Background:

• Avian brood parasitism imposes significant costs on host species.
• Host selection favors individuals capable of rejecting foreign parasitic eggs.
• Egg discrimination is a key anti-parasitism strategy.

Purpose of the Study:

• To investigate egg rejection behavior in the eastern olivaceous warbler (Hippolais pallida) in response to common cuckoo (Cuculus canorus) eggs.
• To determine if egg discrimination always leads to rejection, especially when removal is difficult.
• To explore the role of egg structural strength in avoiding host rejection.

Main Methods:

• Experimental parasitism using model and real non-mimetic cuckoo eggs.
• Video recording of host-parasite interactions.
• Analysis of host pecking and acceptance behaviors.

Main Results:

• Hosts pecked 87% of model cuckoo eggs and 47% of real cuckoo eggs.
• Despite pecking, hosts accepted 43.5% of model eggs and 47% of real eggs.
• Non-mimetic cuckoo eggs were often accepted due to their high structural strength, hindering ejection.

Conclusions:

• Egg discrimination does not always result in rejection when removal is challenging.
• The eastern olivaceous warbler discriminates against, but frequently accepts, non-mimetic cuckoo eggs.
• Parasitic egg structural strength can be a factor in evading host rejection strategies.