As November advances and our part of the globe tilts away from the sun, daylight becomes a precious and a diminishing commodity.
Irish people are essentially tropical animals who have wandered dangerously far to the north. We have to struggle to cope with the winter darkness, though of course we have artificial light to help us. When the only artificial light was fire light November was a more traumatic season. From what little we know about our ancestors who built Newgrange they were obsessed by the death and re-birth of daylight.
The reduction in natural light has an effect on the entire natural world. There is a hormone called melatonin which is remarkable because it is found in animals, plants, fungi and bacteria, as well as in humans. Such universal occurrence suggests it is the most fundamental hormone involved in the evolution of cellular life. Melatonin in all organisms is produced in response to light.
What exactly it does is not fully understood. It’s primary purpose seems to be to protect living organisms from the harmful effects of solar radiation, in particular from ultra-violet light. This is why it’s produced during daylight but not during darkness.
However, it seems to have a lot of secondary functions. In birds and other animals, changes in melatonin levels have been shown to govern many aspects of behaviour, including reproduction, coat growth and camouflage. Similar effects have been documented in plants, where it controls changes in growth. So life at 50 degrees north is undergoing chemical and behavioural changes around now. Bats and hedgehogs react in an extreme manner, retreating to a near-death existence until the light returns. They are the only Irish mammals that go into true hibernation — there is no known case anywhere in the world of a bird that truly hibernates — but they are not alone in their complete capitulation to the reduction in daylight. Frogs, newts and lizards hibernate, so do snails, which also aestivate — a state of suspended animation during hot and dry periods in the summer. Many insects do it, though purist biologists prefer to call this diapause rather than hibernation. Examples include bumble bee and wasp queens and the tortoiseshell butterflies hiding in the curtains in the spare room. Only a few Irish butterfly and moth species hibernate as adults but many more do so as larvae or pupae.
And melatonin levels do have an effect on most birds, triggering dietary changes, migration and moulting. The hens in my poultry run are now laying far fewer eggs and have also started to moult — losing their feathers just when they need them most to keep them warm as temperatures drop.
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