Data from: A brood parasite selects for its own egg traits

Many brood parasitic birds lay eggs that mimic their hosts' eggs in appearance. This typically arises from selection from discriminating hosts that reject eggs which differ from their own. However, selection on parasitic eggs may also arise from parasites themselves, since it should pay a laying parasitic female to detect and destroy another parasitic egg previously laid in the same host nest by a different female. In this study, I experimentally test the source of selection on greater honeyguide egg size and shape, which is correlated with that of its several host species, all of which breed in dark holes. Its commonest host species did not discriminate against experimental eggs that differed from their own in size and shape, but laying female honeyguides preferentially punctured experimental eggs more than host or control eggs. This should improve offspring survival given that multiple parasitism by this species is common, and that honeyguide chicks kill all other nest occupants. Hence, selection on egg size in greater honeyguides parasitising bee-eaters is imposed not by host defences, but by interference competition among parasites themselves.Repeatability of honeyguide egg sizeHoneyguide_repeatability.csvDimensions of honeyguide and host eggsEgg_dimensions.csvData from Experiment 1Experiment1.csvData from Experiment 2Experiment2.csvShell thickness of experimental eggsShell_thicknesses.cs