Have you ever wondered if the moonlight affects birds? Well it does and in many ways. Lunar cycles seem to affect many of the rhythms, temporal patterns and behaviors of birds and other living things on Earth. Ambient light is known to affect visual communication in birds, with the conspicuousness of visual signals being largely determined by the light available for reflection by the sender. We recently discovered that eagle owls Bubo bubo communicate with conspecifics using a patch of white throat plumage that is repeatedly exposed during each call and is only visible during vocal displays.
This is not the first time that animal behaviors have been correlated to the amount of lunar brightness. It is important to highlight that, if moonlight affects communication, the specific effects maybe entirely dependent on the ecology of the species concerned. That is, birds like the lesser-swamp-warbler (above photo) that respond to moonlight conditions may show an opposite pattern to that shown by eagle owls and other birds. For example: call frequencies of nocturnal seabirds have shown to be very low in moonlight and quickly increase when the moon was hidden by clouds. The latter observation may indicate a direct relationship between predation pressure and light levels; and although there is no detailed information about call display patterns, the Mexican spotted owl called more during the last quarter and new moon phases.
Here are 10 facts from various studies about how birds are influenced by the lunar cycle.
1. Eagle Owls use white throat feathers to communicate with each other, on nights with a full moon the feathers are more visible and communication behaviour increases.
2. Northern Saw-whet owls are less active during moonlit nights in order to avoid ending up as potential prey for larger owls.
3. Brau’s Petrels synchronize their journeys to an island mating ground with the full moon. Researchers note that these petrels are also more active in general during a full moon to take advantage of the light to feed.
4. 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 in order to avoid winding up as shark prey.
5. During a full moon, the Whip-poor-will, a nocturnal insectivore, increases its activity levels, vocalizations and nest visiting behavior.
6. Albatrosses are more active during a full moon.
7. Researchers found that lunar cycles affect bird hormone levels. The daily variations in melatonin and cortcosterone disappear during full moons.
8. Another study involving the white-browed sparrow-weaver found that males’ dawn songs started earlier when there was a full moon.
9. A study involving Leach’s Storm petrels suggests that these birds assess predation risk. On nights with a full moon, the petrels remain on their nests to avoid nest predation from gulls that are also more active during a full moon.
10. 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.
Moon Phases, Tides and Birds
Coastal wading birds shape their lives around the tides, and new research in The Auk: Ornithological Advances shows that different species respond differently to shifting patterns of high and low water according to their size and daily schedules, even following prey cycles tied to the phases of the moon.
Many birds rely on the shallow water of the intertidal zone for foraging, but this habitat appears and disappears as the tide ebbs and flows, with patterns that go through monthly cycles of strong "spring" and weak "neap" tides. Leonardo Calle of Montana State University (formerly Florida Atlantic University) and his colleagues wanted to assess how wading birds respond to these changes, because different species face different constraints—longer-legged birds can forage in deeper water than those with shorter legs, and birds that are only active during the day have different needs than those that will forage day or night.
Changes in the daily schedules of tidal flooding affected smaller, daylight-dependent Little Blue Herons more than Great White Herons, which have longer legs and forage at night when necessary. The abundance of foraging wading birds was also tied to the phases of the moon, but this turned out not to be driven directly by changes in the availability of shallow-water habitat. Instead, the researchers speculate that the birds were responding to movements of their aquatic prey timed to the spring-neap tide cycle, a hypothesis that could be confirmed through a study jointly tracking predator and prey abundance.
"Wading birds are a cog in the wheel that is the intertidal ecosystem, and the intertidal ecosystem is driven by tidal forces—everything depends on tides," says Calle. "The nuances of how water levels rise and fall over time and space are very important to understand in order to assess how birds feed. Ultimately, this will help us determine if birds have enough area or enough time to fulfill their energy demands and which areas require greater attention or protection.”
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