In Tangente n⁰42, there was a [Latter, 1902] dataset about the size of cuckoo eggs against the species (goldcrest and warbler) which built the nest. (The whole dataset from Latter is analysed in Maindonald and Braun’s Data Analysis and Graphics Using R, with a degree of caution about how trustworthy this data is…) This is an old reference, but the Wikipedia entry on cuckoos reproduces this finding: “Female parasitic cuckoos specialize and lay eggs that closely resemble the eggs of their chosen host.” Even if Latter’s data is correct and the difference significant, there may be a good explanation for the variability shown in the boxplot below: I would think that it is more likely that subspecies of cuckoos evolved to fit the eggs of different species of birds, rather than a generic cuckoo producing an egg that fits the size of the eggs in the nest it has just landed in!

cuckoo=list(gold=c(19.8,22.1,21.5,20.9,22.0,21.0,22.3,
21.0,20.3,20.9,22.0,22.0,20.8,21.2,21.0),
warbl=c(22.0,23.9,20.9,23.8,25.0,24.0,23.8,21.7,
22.8,23.1,23.5,23.0,23.0,23.1))
boxplot(cuckoo,col=c("gold","wheat"),names=c("goldcrest","warbler"))

(The journal Tangente n⁰42 plots instead a rather inaccurate histogram to deduce that the two samples have different distributions…)