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Can’t fight the moonlight

Maneka Sanjay Gandhi

Moonlight, its presence and absence, affects reproduction, foraging, communication, and other aspects of an animal’s world. Nocturnal animals can hunt or forage more easily under the light of the moon – although venturing out on moonlit nights also comes with the risk of being hunted yourself. From prey behaviour to birdsong – lunar light affects everything.

Lions of the Serengeti in Tanzania are night predators, and are most successful in getting their prey during the darkest phases of the moon. But how do their prey react to the moon’s phases? Scientists from Princeton University put camera traps which spied on the lion’s favourite prey species to see how they reacted to the moon’s phases. African buffaloes, lion prey, form herds as the moon wanes for safety in numbers. Wildebeests appear to set their plans for the entire night based on the moon’s phase. During the darkest parts of the month they stay in a safe place where lions are unlikely to go. As nights get brighter, wildebeests are more willing to venture into dangerous places where run-ins with lions could happen. The routines of zebras and Thomson’s gazelles also change with the lunar cycle. These scenarios in the Serengeti demonstrate the wide-reaching effects of moonlight, a clear example of how the presence or absence of the
moon can have fundamental,
ecosystem-level impacts.

For nocturnal African dung beetles, moonlight is a compass. Once the beetle has located a fresh heap of dung, its main objective is to roll a ball of it away as quickly as possible to the safety of a burrow, to avoid competition from other beetles and potential predators. The quickest route away is a straight line; under moonlight, the beetles make a direct getaway from the dung heap. But in the absence of moonlight the beetles roll their dung balls in
confusion, often landing back into the feeding frenzy.

Marine ecologists have found that in the open ocean, moonlight helps baby fish grow. An otolith is an inner calcium carbonate ear structure in fish, from whose rings one can gauge the fish’s age. By measuring otoliths from 300 triplefins, who swim in New Zealand’s reefs, and comparing them to a calendar, the scientists found that fish grow faster on moonlit nights than on dark ones. If the moon is obscured by clouds, the night counts as a dark one. When the moon is bright, predators such as lantern fish, shy away from hunting baby fish in order to avoid bigger fish that hunt them by light. So these babies may be able to focus on foraging.

But when young fish are ready to return to the coral reef, they do so when the moon is in its dark phase, so that they have a better chance of going undetected by predators hiding in the corals. In fact, scientists have discovered that these fish stay at sea several days longer than normal to avoid a homecoming during the full moon.

Doodlebugs — the larvae of dragonfly-like insects called antlions —run around sandy environments in search of places to catch prey. They dig funnel-shaped holes in the sand in which they sit and wait for prey to fall in. Doodlebugs dig bigger holes around the full moon probably because of the increased activity of prey at this time.

The UV rays of moonlight react with a protein in scorpions that makes them glow in the dark. They hide during full moon and hunt during the new moon’s dark period. Many nocturnal creatures become less active during a full moon period. Rattlesnakes rarely leave their burrows when the moon is full, to protect themselves from predators.

Moonlight also impacts mating behaviour Badgers urinate to mark territory when they are getting ready to mate. They do this when the moon is new, probably because the darkness allows their prolonged mating more security from predators. During the full moon period, badger urination is much less.

Certain owl species become more active during the full moon, both in their mating calls and in showing off their feathers to potential mates – probably since owl feathers are more visible in the light of a brighter moon. On the other hand call frequencies of nocturnal seabirds are very low in moonlight and quickly increase when the moon is hidden by clouds. And, small Northern Saw-whet owls are less active during moonlit nights to avoid ending up as the prey of larger owls.

Moonlight also influences animals that are active in daytime. Sparrow sized white-browed sparrow weavers in South Africa’s Kalahari Desert live in family groups and sing together to defend territory. But during the breeding season, males also perform dawn solos and, when a full moon is visible, they get up even earlier and sing much longer. This reduces as the moon wanes.

For many animals, particularly birds, the moon is essential to migration and navigation. A study from Lund University in Sweden shows that the presence or absence of moonlight has a considerable bearing on when migratory birds take flight in autumn.

Scientists at Lund University studied European nightjars and how the lunar cycle and moonlight affects the departure time when the birds start their three-month-long migration flight to areas south of the Sahara. They found that the birds are more than twice as active in their hunt for insects during moonlit nights compared with when it is dark. The study also shows that the birds begin their autumn migration southwards ten days after the full moon – no matter where they are.

A Japanese study involving streaked shearwaters determined that this marine bird flies for longer periods and lands on water more often during nights with a full moon. However,
researchers reported that sharks also take advantage of the increased light, so the shearwaters don’t remain on the water for long to avoid winding up as shark prey.

Researchers find that lunar cycles affect bird hormone levels. The daily variations in melatonin and corticosterone disappear during full moons. During a full moon the Whip-poor-will, a nocturnal insectivore, increases its activity levels, vocalisations and nest visiting behaviour. Albatrosses are more active during a full moon. A study involving Leach’s storm petrels suggests that these birds assess predation risk. On nights with a full moon the petrels remain in their nests to avoid nest predation from gulls that are also more active during a full moon. The swallow-tailed gull, a nocturnal seabird of the Galapagos islands, is most active during the new moon phase when its prey is closest to the water surface.

According to a study by the Colorado State University Veterinary Medical Center, dogs and cats are more likely to need medical attention during the days surrounding a full moon. Cats are 23 percent more likely to visit an emergency room during these days, and dog visits increase by 28 per cent.

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