Liénard A, Gil D, Canal D, Monclús R. 2025. Data from: Nest-host selection and parasitic nestling survival in the spotless starling (Sturnus unicolor). Behavioral Ecology and Sociobiology.

Conspecific brood parasitism is an alternative reproductive tactic in birds. It occurs when some females lay their eggs in conspecific nests and rely on the hosts to raise their offspring. Parasitic females lack control over the outcome of their reproductive event beyond their investment in egg production. However, they might select when and where to lay their eggs to increase their chances of success. Here, we used a breeding colony of spotless starlings (Sturnus unicolor) in Spain to explore the patterns of host nest selection by parasitic females. We used data from eight breeding seasons, during which we recorded all parasitism events. We hypothesized that both conspecific brood parasitism and parasitic nestling survival are influenced by host characteristics and brood timing, but not necessarily in the same direction. We found that most parasitic events happened during the first clutch wave of the season, at the beginning of host clutch laying, and that parasitic females laid their eggs synchronously with the rest of the colony. Furthermore, parasitic eggs were more often found in nests containing eggs of similar size, probably due to the ejection of dissimilar eggs by hosts. Parasitic eggs laid early in the host laying sequence were more likely to hatch, and those that hatched were more likely to fledge when laid in synchrony with the wave peak of the colony. Whether parasitic females use public information to select those host nests and time windows that offer higher chances of offspring survival is a question that deserves further research.