The clocks went back; the nights, which have been getting longer since the autumnal equinox, will seem extra long and especially dark now. We cosy up in front of the fire and crave stodgy puddings but out in the park, the ratio between daylight and dark triggers many natural processes.
For instance, the frequency at which some species of songbirds sing can depend on the length of daylight hours. In the spring, as daylight hours are increasing, the male bird produces more hormones, particularly androgens; as a result song frequency increases. During the autumn, when the hours of daylight are decreasing, the process is reversed, the bird’s androgen levels drop dramatically and singing frequency slowly decreases.
Two of the park’s songbirds: a blackbird and a song thrush.
Not only is the singing frequency of these species dependent on the amount of daylight, but the song repertoire is, too. In spring, when the daylight hours are increasing, birds sing a wider repertoire of more complex songs; in the autumn, as daylight hours shorten, there is a reduction in song repertoire and complexity.
This time of year, between the equinox and the winter solstice, it can feel as if the park has fallen asleep in the mud, under a blanket of fallen leaves. But the winter solstice will fall on Monday, December 21st, and in January, the blackbirds will begin to sing in response to the lengthening daylight hours, signalling the year’s turn.