Nest design as an adaptative tool to escape brood parasitism
1. Nest characteristics vary depending on environmental factors but may also be influenced by between-species interactions. As a defence against avian brood parasites, hosts can evolve specific nest architecture to minimise risks of brood parasitism by preventing access to the nest cup or reducing the success of the parasite chick.
2. The common redstart (Phoenicurus phoenicurus) is a regular host of the common cuckoo (Cuculus canorus), and due to its cavity-nesting behaviour, cuckoo eggs are often laid outside the nest cup and consequently unsuccessful. This allowed us to test (i) if cuckoos prefer certain host nest designs and (ii) if redstart nest design can reduce the probability of successful brood parasitism.
3. While recording brood parasitism events in two redstart populations, we documented nest cup characteristics, such as internal dimensions, materials used and position within the nest-box, as well as the distance and angle between the nest cup and the nest-box entrance hole.
4. We found that cuckoos preferred bigger nest cups, possibly targeting high-quality individuals, and nest cups that were built higher than the rim material, which may contribute to an easier eviction of the host eggs/nestlings. Redstarts, on the other hand, reduced successful brood parasitism by placing nest cups further from the cavity entrance, but also selecting cavities with relatively smaller entrances.
5. We show the importance of host nest design influencing the coevolution between hosts and brood parasites. Redstarts seem to adopt nest design strategies to decrease brood parasitism risk, while cuckoos’ preference for certain aspects of redstart nest design may be shaped by a conflict between female laying success and chick eviction success. Hosts’ and brood parasites’ frontline strategies may then shape host nest characteristics and parasite’s preferences, impacting their co-evolutionary arms-race.