Light Pollution Abatement Site Calgary Centre Royal Astronomical Society of Canada

Light and Animals

Artificial nighttime lighting changes animals' behaviour. Some animals shun lit areas while others take advantage of the light to forage or hunt at the expense of other species. Everyone has seen moths clustering around outdoor lights - attracted to the brightness when they should be looking for a mate. This situation looks like a feast for bats, but some species of bats shun lit areas so the natural balance of bat species can be skewed by nighttime lighting.

Owls are supremely adapted to hunting in nearly total blackness, but lose that advantage over rodents whenever there is man-made light available.

Many large shy predators avoid lit areas altogether. These animals need dark passageways to go from one hunting field to another - a lit roadway can act as a fence, cutting their territory in half.

Lit Buildings Can Kill Birds

Most of our songbirds migrate at night. Unfortunately, warblers can be confused by artificial night time lights and often collide with lit structures. Birds are reluctant to fly out of the lighted area into the dark, and often continue to flap around in the beam of light until they drop to the ground from exhaustion. For this reason, such obstacles should not be lit overnight.

In the natural world, light areas represent the passageways.

Lit windows fool birds into colliding with them.

Light and Hormones

Light at night affects the normal melatonin levels produced in the pineal gland. This hormone, melatonin, is responsible for controlling the day-night changes in hormones that affect sleep and the immune system. Melatonin also directs the seasonal changes in sex hormones that rule animals mating season. Change the light levels at night and one can change the course of history for a species.

Light at night can allow young male Deer Mice to become sexually mature later into the Fall, when normally the shorter nights cause young mice to delay sexual maturity until the following Spring, when more food is available. Light at night increases the testosterone levels in these animals through the modulating effects of melatonin.

Experiments on rats and hamsters showed that continuous nighttime light advanced the onset of puberty in females compared to rats that experienced normal day-night cycles. Besides a variety of rodents (which are an important food source for carnivores), this effect is also true in female cattle, sheep, goats and horses.

Studies on both male and female Rhesus Monkeys indicate that significant alteration of hormones levels and the timing of sexual maturity can accomplished by modifying the natural day-night cycle length. This effect has also been noted in humans, where long nights correspond to higher melatonin levels and decreased ovarian activity and conversely, short nights (or light at night) correlate to increased ovarian activity.

These effects can be passed on to offspring. Studies on Meadow Voles show that the young of mother voles that have been exposed to light at night develop less quickly (both weight and sexual maturity) than litters of mother voles that have experienced long nights.