The common cuckoo Cuculus canorus is divided into host-specific races (gentes). Females of each race lay a distinctive egg type that tends to match the host's eggs, for instance, brown and spotted for meadow pipit hosts or plain blue for redstart hosts. The puzzle is how these gentes remain distinct. Here, we provide genetic evidence that gentes are restricted to female lineages, with cross mating by males maintaining the common cuckoo genetically as one species. We show that there is differentiation between gentes in maternally inherited mitochondrial DNA, but not in microsatellite loci of nuclear DNA. This supports recent behavioural evidence that female, but not male, common cuckoos specialize on a particular host, and is consistent with the possibility that genes affecting cuckoo egg type are located on the female-specific W sex chromosome. Our results also support the ideas that common cuckoos often switched hosts during evolution, and that some gentes may have multiple, independent origins, due to colonization by separate ancestral lineages.

No abstract

Summary Juvenile birds differ from conspecific adults in their diet and methods of prey capture and prey handling. Juvenile‐adult differences in foraging result from (1) immaturity of the beak, skeleto‐muscular and neurological systems and (2) the time required to learn foraging skills. These conclusions are largely based on field observations. More experimental studies to assess the relative importance of the various constraints are needed. Juvenile birds appear to be under strong selection to reach adult form and function as rapidly as possible. Remaining differences between juveniles and adults are largely attributable to constraints. In contrast to many other taxa there are few examples in which juvenile‐adult differences in foraging have been accentuated by selection on the juvenile behaviours.

No abstract