Moskat and Honza (2000) studied the interrelationship between the cuckoo (parasite) and Great Reed warbler (host). In their research, ninety nesting sites were observed. Thirty-one nests (34%) went un-parasitized, thirty-seven nests (41%) were parasitized only once, and twenty-two nests (24%) were parasitized numerous times.
Statistically speaking, the differences observed between the single- and multiple-parasitized nests were weakly significant and attributed to chance alone.
Which of the following factors BEST explains these data?