Cuckoo Cuculus canorus in Bulgaria

The Cuckoo is observed on the entire territory of Bulgaria. The density of its population depends above all on the abundance or absence of food in a given area, and then on the availability of suitable other birds' nests for the purpose of laying eggs. The first Cuckoos appear from the south at the end of February, almost 2-2.5 months earlier than the main part of the population. They are few in March - all in all 0.84 % of the whole numbers of individuals observed in the country throughout the year. There is a well-marked migration in April (14.65%) and especially in May (38.03%), when most Cuckoos of the Bulgarian population are already actively parasitizing. Approximately 100000 pairs of Cuckoos live within the country. At an average, a pair can parasitize upon an area of 1.11 km2, in the nests of 79 pairs of host-birds. There is a permanent struggle between the parasite and the hosts. The Cuckoo must constantly change its hosts. More than 2300 years ago, on the territory of the Bulgarian lands of nowadays and the adjoining regions, the main «tutors» of the Cuckoo were the Pigeons and Doves (Columbiformes), the Warblers (Hippolais) and Crested Lark, in the middle of the XVI century - the Lesser Whitethroat, and at present in Bulgaria the Cuckoo lays eggs in the nests of 28 bird species, mostly in the nests of the Great Reed Warbler (30.11%), Robin (8.6%) and Corn Bunting (6.45%). It parasitizes for 71 days- from April 25th to July 4th. The period of flying out of young Cuckoos is stretched for so long, only that the timeframes are shifted backwards with one month approximately. The Cuckoos lay 82% of their eggs in June and May. A half of the young Cuckoos fly out in July. The adult Cuckoos from the Bulgarian population fly away at the end of June - beginning of July. Afterwards an abrupt diminishing of the species numbers is observed. The Cuckoos are observed in Bulgaria for 228 days, i.e. from the spring arrival of the first individual (26th February) until the autumn departure of the last one (11th October). Bulgaria and the neighbouring regions of the Balkan Peninsula are an important crossroads for a mass night spring and autumn migration between the Euro-Asian breeding areas and the African winter quarters of the species.