A1 Refereed original research article in a scientific journal
Cuckoos overcome cavity-nesting host defences with alternative egg deposition modes
Authors: Kysučan, Michal; Tolvanen, Jere; Samaš, Peter; Miller, Ryan; Rutila, Jarkko; Thomson, Robert L.; Grim, Tomáš
Publisher: Elsevier BV
Publication year: 2026
Journal: Animal Behaviour
Article number: 123548
Volume: 235
ISSN: 0003-3472
eISSN: 1095-8282
DOI: https://doi.org/10.1016/j.anbehav.2026.123548
Publication's open availability at the time of reporting: No Open Access
Publication channel's open availability : Partially Open Access publication channel
Web address : https://doi.org/10.1016/j.anbehav.2026.123548
The precise method by which brood parasites deposit their eggs into host nests has been discussed in the natural history literature for centuries. In this study, we explored the common cuckoo, Cuculus canorus –common redstart, Phoenicurus phoenicurus , parasite–host system, where alternative egg deposition modes can be expected. We video-recorded two egg deposition modes used by cuckoos to overcome cavity-nesting of redstarts. Three-quarters of cuckoos used entrance laying: the female laid while being perched at the cavity entrance. Entrance laying was risk-free with regard to the female getting stuck in the cavity and resulted in low nest desertion by hosts, but had low reproductive fitness due to frequent mislaying of eggs outside the nest cup. The remainder of cuckoos laid directly into the nest cup after entering the nest cavity. Direct laying was the more effective mode with higher reproductive success, but it was associated with higher risks of host nest desertion and the cuckoo female getting stuck inside the cavity. We provide the first direct evidence that brood-parasitic cuckoos use alternative egg deposition modes and quantify their fitness consequences.
Funding information in the publication:
This study was supported by the Czech Science Foundation (grant nos P506/12/2404 to TG and PS, 22-26812S to PS and HFSP RGY83/2012 to TG), student project of Palacký University (grant no. 2014/013 to MK and TG), the Academy of Finland grant (project no. 138049) and University of Turku Collegium for Science and Medicine grant (to RLT).
