Can Skylarks Alauda arvensis discriminate a parasite nestling? Possible case of nestling Cuckoo Cuculus canorus ejection by its host parents

The Common Cuckoo Cuculus canorus is an obligate brood parasite and many studies have dealt with egg rejection by host species. However, evidence for ejection of Cuckoo nestlings by host parents has not been reported. Here we describe an observation of a Skylark Alauda arvensis pair that probably ejected a young Cuckoo and subsequently raised their own offspring. This was the only case we detected Cuckoo parasitism among 348 Skylark nests in our study area in the northern Netherlands, while we found about 21% of 43 Meadow Pipit Anthus pratensis nests being parasitized by Cuckoos.