Flexible mating patterns in an obligate brood parasite

Abstract

Polygamous mating is expected to occur in obligate avian brood parasites because the lack of parental care reduces the need for a stable reproductive bond. Unlike nesting species, an absence of the constraints resulting from raising offspring might also favour a flexible mating system that adjusts to changing ecological conditions. Information on brood parasites' mating systems and their spatio‐temporal variation is, however, still scant. Here we analysed the genetic mating patterns of Great Spotted Cuckoos Clamator glandarius in two populations in northern and southern Spain and compared the results with those of previous studies. Parentage analyses showed high levels of polygamy in both populations that contrast with a prevalence of monogamy previously reported in the southern population. We suggest that the differences arise from an increase in population density, which in turn increases the probability of intraspecific encounters and therefore opportunities for mating. We also found that a greater number of mates increased the number of offspring produced, both in males and in females. The increase in offspring production in females might be the result of enhanced fertilization success during the lengthy laying period. Our data, combined with previous reports, demonstrate plasticity in the genetic mating patterns of the Great Spotted Cuckoo that may be associated with large fluctuations in population density.