When the male arrives in the spring he is ready for breeding and begins immediately, or shortly after his arrival, to search for a suitable territory, an area surrounding an acceptable nest. The time of breeding is regulated entirely by the amount of light the bird is exposed to at that particular time of the year.
The male normally guards 2 3 nests in the area and sings from them. His song performs the very important function of declaring the territory by marking out where it is and chasing away rivals. He will often sing during or after a battle. Sunrise is the most active time for singing, morning-to-midday is quieter, and sunset sees something of an upsurge again. The pied flycatchcr is a very diligent singer, and according to research carried out by a Finnish ornithologist, this bird goes through its repertoire over 3620 times per day, which on average is once every 18 seconds during day light hours.
Any strange bird, pied flycatcher or otherwise, which enters the territory is driven away. Fights between the males can sometimes be very tierce, and on two occasions I have found dead males in breeding areas. In one case in 1964. a male pied flycatcher came and drove away a blue tit u hich was already occupying a nest box in which it had laid an egg. The flycatchcr in its turn energetically defended his new nest box, which was evidently a very sought-after residence. During one of his battles with another pied flycatcher, he was driven back into the box seriously wounded and died there.
If a female pied flycatcher occupies a nest which already contains eggs or dead young she will quite simply build her nest on top of them. The great tit in particular seems to fly from its nest whenever a pied flycatcher appears, although those with full clutches put up more resistance.
The following notes were made about birds driven from their nest boxes by pied flycatchers between 1956 and 1977: In 1957 a crested tit was driven away after it had been sitting on its five eggs for a week. A female pied flycatcher built its nest on top of these eggs, laid its own eggs, and reared its brood of young. In 1963 and 1964, one pied flycatcher was driven away by another when it had just begun to build its nest. A blue tit was also driven away in 1964 when it was beginning its building. In 1974 a flycatcher built its nest in a tit type box and laid two eggs. This box had split during the winter and because I was working in another area I had not been able to repair it. On a blustery day it fell to the ground. A great tit was silling on five eggs in a neighbouring box but was soon driven out by the homeless flycatcher which buill its own nest on top of the tit eggs and laid six eggs which eventually produced six fledged young. The dispossessed great tit moved lo yet another nearby box and built a new nest. The same thing happened in 1975. although this time the great tit had built her nesi and laid her eggs but had noi yet started incubation. On a further ten occasions greal lits were ousted from iheir boxes by pied flycatchers just as they were starting to build nests or had only half completed them.
Each species of bird searches instinctively for the particular type of habitat which best suits it. One might imagine that this would lead lo overpopulation in the most favoured area, but in actual fact a balanced distribution occurs. If a population of birds isexpanding, the best niches are colonized first and only afterwards, as the number of individuals in the area increases, are the somewhat less favoured places occupied. So instead of the best placcs becoming overcrowded, the population is squeezed out into less popular outposts.
Both the male and female take part in defending territory, with the male dealing most vigorously with males of the same species or male tils. Both will issue warnings against crows, woodpeckers, squirrels, humans, etc.. and will protect their nest against them.
In my research area, pied flycatcher territories measure on average I500sq-m(50 * 30 m). When the young start to fly, the boundaries of the territory melt away and the family moves into the surrounding area to find food.
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