Amphibians around the world synchronise their mating activity by the full Moon, researchers have discovered.
This global phenomenon has never been noticed before, but frogs, toads and newts all like to mate by moonlight.
The animals use the lunar cycle to co-ordinate their gatherings, ensuring that enough males and females come together at the same time.
In doing so the creatures maximise their spawning success and reduce their odds of being eaten.
Details of the discovery are published in the journal Animal Behaviour.
Biologist Rachel Grant of the Open University was studying salamanders near a lake in central Italy for her PhD in 2005 when she noticed toads all over the road, under a full Moon.
"Although this might have been a coincidence, the following month I went along the same route every day at dusk and found that the numbers of toads on the road increased as the Moon waxed, to a peak at full Moon, and then declined again," she says.
A review of the scientific literature found little mention of any similar records, so Grant returned to the same site in 2006 and 2007 to survey the amphibians in more detail.
She then collated her data with a 10-year analysis of the mating habits of frogs and toads at a pond near Oxford, UK, collected by her supervisor Tim Halliday, and with data on toads and newts living in Wales collected by colleague Elizabeth Chadwick from Cardiff University, UK.
"We analysed the data, and found a lunar effect at all three sites," Grant says.
A cue to reproduce
For example, the common toad (Bufo bufo) arrives at all its breeding sites, mates and spawns around the full Moon. The common frog (Rana temporaria) also spawns around the time of the full Moon.
"Newts also seem to be affected by the lunar cycle but the results are less clear," says Grant.
Newt (Lissotriton vulgaris, L. helveticus and Triturus cristatus) arrivals peak during both the full and new moons.
But "newts appear to avoid arriving at the breeding site when the Moon is in its third quarter. This could be because the Earth's magnetic field is highest at that time. More research is needed to clarify this," Grant says.
The researchers have also looked at historical data collected in Java on the Javanese toad (Bufo melanostictus) and found that it too mates by the lunar cycle, with females ovulating on or near to the full Moon.
"We now have evidence of lunar cycles affecting amphibians in widespread locations. We definitely think that Moon phase has been an overlooked factor in most studies of amphibian reproductive timing," says Grant.
Toads also get in on the act
"We think this may be a worldwide phenomenon. However, differences between species in ecology and reproductive strategy may mean that not all amphibians are affected in the same way. This is something we would like to investigate further."
Grant and her colleagues now hope to produce a statistical model that takes into account weather factors and other environmental variables such as geomagnetism, as well as the lunar cycle.
Making accurate predictions of mass amphibian movements is important in their conservation, she says. For example, roads could be closed at precise times to avoid cars killing thousands of mating frogs and toads.
"Given the current global crisis among amphibian populations, further understanding of [their] breeding behaviour is extremely important," she says
