Egg laying behavior of common cuckoos (Cuculus canorus): Data based on field video-recordings

The egg laying behavior of brood parasites is at the heart of studies on host co-evolution. Therefore, research on egg laying behavior can improve our understanding of brood parasitism and associated processes. Over a seven year study period, we monitored 455 oriental reed warbler (Acrocephalus orientalis) nests during the egg laying period, 250 of which were parasitized by common cuckoos (Cuculus canorus). We collected 53 clear videos of common cuckoo parasitism, analyzed all recorded parasitic behavior in detail, and summarized the process of brood parasitism. Furthermore, based on analyses of the field video recordings, we propose a new explanation for egg removal behavior, namely the delivery hypothesis, i.e., egg pecking and biting by cuckoos may facilitate fast egg-laying and parasitism by reducing host attention and attack, with egg removal a side effect of egg pecking and biting. We concluded that common cuckoos change their behavior when hosts are present at the nest, with a set of behaviors performed to deal with host attack and successfully complete parasitic egg-laying regardless of time of day.