BY THE BAY: The importance of light and dark
It is a pleasure to see the first, warm colours of spring emerging in the landscape, signs that the days are slowly lengthening. Bright yellow hazel catkins dangle over forest paths. Vibrant swathes of orange and crimson are revealed on closer view to be the fresh shoots of willow and red-osier dogwood. Copious male catkins on the alders are turning these seed-prolific trees a warm red. They attract wandering flocks of pine siskins and redpolls, small birds that dangle acrobatically from the thinnest of branches. Red-winged blackbirds are beginning to sing in the marshes, staking out their territories for the coming season, and some migrant swallows have already arrived.
These sights and sounds are so familiar that we take them for granted. Yet what causes nature to begin the season, right on cue? The critical factor is not the temperature or amount of sunshine but the longer hours of daylight as the earth turns on its axis. Day length stimulates hormone production in birds, leading to breeding and migration. That is why male red-wings suddenly start flashing those bright colours and singing their hearts out in the reed beds, even with frost on the ground. Conversely, the length of uninterrupted darkness at night governs such biological activities as growth and dormancy in trees and many other plants, the timing of deer mating, and how salmon migrate (migration has been observed to peak during the darker nights of the monthly lunar cycle). Darkness fosters the production of melatonin in animals, a hormone that affects sleep cycles, body temperature and immunity to disease.
The awareness of light for timing life’s activities is not a matter of “seeing” in the normal way. Plant leaves have light-sensing proteins and pigments. Birds perceive light at red wavelengths, which pass through the skull directly to special receptors in the brain. Like other animals, including humans, they also have light-sensitive cells in the eye’s retina which are not involved in vision. Our bodies are aware of the quality and quantity of light around us, without our conscious knowledge.
Natural darkness has been entirely banished in some parts of our communities. Disrupted rhythms of light and dark can have a negative effect on wildlife, ecosystems and humans, with constant overexposure to artificial light at night being particularly detrimental. To maintain your own healthy lifestyle, enjoy long walks in the spring sunshine and sleep in a dark room at night.
Anne Murray, the author of two nature books available in local book stores, writes monthly in the Peace Arch News – www.natureguidesbc.com