The collared flycatcher, Ficedula albicollis, and the pied flycatcher, F. hypoleuca are two closely related species of bird. DNA analysis has shown that speciation from a common ancestor occurred approximately 1 million years ago. A study was carried out on the island of Öland, Sweden. In Öland, the breeding areas of the two bird species overlap and small numbers of hybrid flycatchers are produced. • Birds were captured and their DNA was analysed to identify whether each bird was F. albicollis, F. hypoleuca or a hybrid. • Sperm samples were taken from the male birds. Table 3.1 shows the percentage of males of each bird type with normal sperm. Table 3.1 bird type | percentage of males with normal sperm ---|--- F. albicollis | 68 F. hypoleuca | 78 male hybrid | 0 • The researchers observed that female birds mostly choose mates of their own species based on plumage (feathers) and song. • Hybrid flycatchers are produced when female F. albicollis mate with male F. hypoleuca that have a song that is similar to F. albicollis. • Analysis showed that all female hybrids were sterile. The group of eggs a female bird lays at a single time in its nest is called a clutch. The offspring in the nest are looked after by a male-female pair. Sometimes the male in the male-female pair does not provide the sperm that fertilise the eggs of the female. Table 3.2 shows: • the percentage of clutches with eggs that hatched • the percentage of extra-pair nestlings (offspring in the nest fathered by a male that was different from the male of the male-female pair). Table 3.2 parents of nest | percentage of clutches with eggs that hatched | percentage of extra-pair nestlings male | female | | ---|---|---|--- F. albicollis | F. albicollis | 94.5 | 17.2 F. hypoleuca | F. hypoleuca | 89.3 | 22.4 hybrid | F. albicollis or F. hypoleuca | 38.0 | 100.0