Dr. Nicholas Dodman
The belief that lunar cycles can and do influence aspects of behavior has existed since Roman times. Despite recent attempts to establish the validity of this concept, none - bar one - has produced any convincing evidence to support it. The one affirmative study concluded that schizophrenics are more troubled at full moon than at other times. The results of this study were statistically significant. Most human studies, however, have concluded that there is little or no effect of the phases of the moon on behavior, so positive findings on this subject is, at best, few and far between. But what of our pets? More attuned to their environment, as they are, might they be influenced, however slightly, by the phases of the moon? "Maybe," is the answer to that question though no one has successfully demonstrated this influence. Belted sandfish have significantly higher levels of an estrogen-like substance in their bloodstream at new and full moon.
Evidence Provided from Study of Other Species
Some species do show a few signs of influence:
Night-migrating skylarks are most active when the moon in its waxing gibbous stage.
Galapagos fur seals dive less and deeper on moonlit nights than at new moon and show loss in body weight.
The predatory behavior of some mites is significantly and strikingly depressed around the full moon.
Coho salmon parrs and smelts, maintained in a fixed 12-hour light/ 12-hour dark light cycle, show rhythmic changes in growth pattern on a 14–15 day cycle suggesting that the lunar cycle acts as a "timegiver" for the synchronization of growth rate rhythms.
One type of mollusk can derive directional cues from the magnetic field of the earth and will orientate differently according to the lunar phase.
Tides, which are affected by lunar cycles, effect the behavior of many ocean creatures.
Possible Reasons why Animals Might Behave Differently during Different Lunar Phases
Changes in nocturnal illumination causing changes in sleep/wake cycles and/or behavior of the animal itself, either directly or by altering the behavior of the animal's prey/competitors.
Changes in total daily illumination affecting pineal gland function (located in the brain) and thus altered neurohormone activity.
Changes in the Earth's magnetic field affecting internal magnetoreceptors.
Evidence That Domestic Pets May be Affected by Lunar Cycles
There is no concrete evidence to this effect; however, anecdotes abound and some seem to have a reasonable explanation. For example, a client's cat apparently sprayed a lot of urine when there was a full moon. The cat's owners were lobster fishermen and were thus always highly aware of the weather and tides. Why might a cat spray more on a moonlit night? Possibly because of increased activity of outdoor critters facilitated by the moonlight or because of the intruders' increased visibility to the indoor cat. Was the cat a lunatic? I don't think so. It might have behaved differently during a full moon but there was a reasonable explanation for its increased agitation at this time.
Presumably the same might hold true for dogs. Coyotes and wolves are often depicted howling at the moon. One might imagine that hunting would be better on a moonlit night and that there would thus be increased activity of these wild canids under such conditions. Though they have excellent night vision, neither dogs, wolves, nor coyotes can see when there is no light, but full moonlight, creates virtually daylight visibility for them. Howling is a long distant communication, with members of a group signaling their location to each other by this means. Dogs may howl on moonlit nights because they sense increased movements of other animals and feel a greater the need to communicate their position. Others might anticipate the thrill of the chase and become generally more restless or agitated.
Even we humans can be driven to act by primordial instincts that we barely appreciate or recognize. Dogs probably have even greater genetically imbued subliminal agendas than we do. Perhaps dogs that howled on moonlit nights remained in better contact with their pack members and that this behavior somehow conferred a survival benefit. The precise benefit may have been linked to increased activity of prey on moonlit nights, hence a greater need for strategic communication on these potentially fruitful nights.