As I approached the wooden observation hut where my video camera was situated, I saw the familiar herd of fallow deer. An old hind rose slowly to her feet – a signal for the rest of the herd to follow her quietly down the valley. Their lack of fear no longer surprised me since I had become a regular feature of their landscape.
Gaining the trust of wild animals is one of the great bonuses of a long-term field study of their behaviour. But it was the badgers not the deer that I was filming as part of my research into how phases of the moon affect their behaviour.
A mystery to solve
My investigations started five years ago in Plymouth, when a friend asked me to help solve a mystery. He was puzzled by tracks in the long grass beyond his garden wall and, knowing of my interest in filming nocturnal wildlife, asked me to set up my camera.
The patch of grass was part of an area of overgrown land that had previously belonged to the Ministry of Defence (MoD), and which had become an unofficial nature reserve. Within its boundaries a wide variety of wildlife flourished, including kingfishers, barn owls, slow worms, glow worms and beautiful plants, such as marsh orchids.
It took only a single night’s filming to reveal that the tracks were evidence of the night-time ramblings of a group of badgers.
Having badgers so close proved a great temptation and we began putting out peanuts to extend the time the badgers spent in front of the camera. Unlike the hedgehogs and foxes I had videoed previously, badgers follow regular foraging paths each night, which makes them ideal filming subjects.
At first I was happy just to film them feeding, but soon I was drawn into a more detailed study of the badgers and other wildlife whose nightly dramas were played out in front of my lens.
The disappearing runt
When the study began in February 2000, just four badgers were regularly visiting the feeding area. There was a dominant female, distinguished by a missing right ear lug, who I estimated to be two years old. There was also an adult male in tip-top condition, and two yearlings – a well-grown female and an undersized individual.
This ‘runt’ disappeared after only a few weeks – I assumed that it was too weak to survive the winter. Its loss was compensated for in early May by the appearance of three boisterous cubs, which dominated the feeding station until they were weaned in late June, when they were forced to forage further afield.
They were clearly the offspring of the one-lugged female, but were regularly accompanied to the feeding station by other group members, including the dominant boar.
Comings and goings
The original yearling female disappeared in October – probably to join another group – at about the same time as a mature boar joined my gang. So, what started as just four animals in February had become six by the end of the year.
This pattern was repeated in subsequent years with more cubs being reared in 2001 and 2002, which swelled the group size to a maximum of 12 animals.
While watching the changing social dynamics of the group, I began to notice patterns in the animals’ behaviour, particularly in relation to the moon.
The power of the moon
In my day job as a marine biologist, I’ve learned about countless marine animals, fish and invertebrates whose reproductive cycles are controlled by the phases of the moon.
But I was struck by the paucity of data on whether terrestrial species were similarly affected. For example, there was virtually nothing in the mammal literature on lunar cycles apart from some mainly anecdotal reports of extreme human behaviour around the time of full moon (lunacy), and a number of articles dealing with predator-prey relationships.
For example, many prey species – rodents, rabbits and the like – are less active at the time of full moon to reduce the risk of being seen by predators, which in turn means that their predators also tend to be less active on moonlit nights.
The moon clock
Few people can fail to be struck by the dramatic changes in night-time light levels that accompany the lunar cycle. Given its relatively short duration (29.54 days), it seemed odd to me that more species, especially nocturnal mammals, were not using the lunar clock as a natural chronometer to regulate or synchronise fundamental aspects of their biology.
My badger family were to provide me with important new insights into this relationship.
When a badger approached the feeding station, it usually laid scent on a grass tussock or stone using its subcaudal gland, located beneath its tail. This would take about a second and would be accompanied by a characteristic bending of the knees and raising of the tail – easy to distinguish on film.
It was also common for them to squat-mark again, usually at a different place, as they prepared to leave the feeding station. This fits with the idea that such marking places serve as information boards for the group.
On occasions, boar badgers also performed raised-leg urination (similar to that seen in dogs), another part of their scent-marking repertoire. Urination was sometimes used to overmark the scent traces left by a visiting fox.
Over the weeks of study, I began to notice a trend. The dominant male and female would scent-mark more often at times of a new moon than at other times.
I also noticed that the female’s attitude to the male members of the group varied depending on the phase of the moon. This ranged from tolerance or indifference when the moon was new, to hostility when it was full. Moreover, the actual mating events I recorded took place predominantly during the lunar ‘dark phase’.
My investigations thus suggested that reproductive behaviour in badgers is strongly influenced by the lunar cycle.
In the dark
Unlike those fish and invertebrates I was familiar with, which reproduce at or around the time of the full moon, reproductive behaviour in badgers appears to be restricted largely to times when the moon is in the dark phase. This discovery is a first for any species of nocturnal mammal and opens up an exciting new area for future research.
Another striking discovery was that badgers tended to be more active on dark phase nights (a tip for badger watchers), as measured by the number of visits to the feeding station. However, this difference in activity levels was not sufficient to explain the fluctuations I observed in reproductive behaviour.
Badgers are our largest terrestrial carnivore (omnivore is more accurate), with no natural enemies, so why would they hide during the light phases of the moon? Were they less active because of the absence of prey?
I investigated this by looking at the activity patterns of the earthworm Lumbricus terrestris, which makes up a large part of the badger’s diet. But the presence of earthworms on the soil surface at night, where badgers normally find them, had more to do with weather conditions. They appeared whenever it was damp, whatever the light level.