Cuckoos parasitize many rare and inconspicuous host species but avoid other common and conspicuous ones. In this article, results of a study that solved this long-standing ecological conundrum are described. I use this work to illustrate va - rious weaknesses of typical ecological studies (sample size, data representativeness, reification) and give suggestions for a better research practice in the future. and Jiří Klimeš, Ivan Literák.