Does clutch variability differ between populations of cuckoo hosts in relation to the rate of parasitism?

To aid discrimination of mimetic cuckoo eggs, hosts of avian brood parasites would theoretically benefit by laying clutches that are more uniform in appearance and by laying clutches that differ from those of other females in the population. Support for these hypotheses is equivocal, particularly amongst studies that have utilized reflectance spectrophotometry; quantitative studies comparing clutch variation between parasitized and unparasitized host populations have supported these hypotheses, whereas experimental studies comparing clutch variation between rejector and acceptor individuals within a population generally have not. Here we extend the approach of comparing population differences in clutch variation by asking whether parasitized populations that suffer relatively higher parasitism rates, and are therefore subject to more intense selection for host defences, show lower within-clutch variation and higher between-clutch variation than populations with low parasitism rates. We used reflectance spectrophotometry to compare clutch variation in two hosts of the pallid cuckoo, Cuculus pallidus, each of which exhibits two geographically distinct subspecies that differ in parasitism rates (red wattlebirds, Anthochaera carunculata, and yellow-throated miners, Manorina flavigula). A third host species, the yellow-tufted honeyeater, Lichenostomus melanops, was included as a control. Our results do not support either hypothesis, and are consistent with experimental studies that also failed to support the hypothesis, casting doubt on the generality of these processes.