Defecating in the Moonlight: Links between Lunar Phase and Latrine Use by European Badgers

Student Spotlight - Will Cresswell

Undergraduate Research at the University of Bristol

Email: wjcresswell@googlemail.com   

I’m a 3rd year student studying Zoology at the University of Bristol. My dissertation partner Cosmo Robertson-Charlton and I have been studying the ecology of urban badgers (Meles meles) in Bristol. In particular, our research focused on the relationship between lunar phase and latrine use by badgers and I'm excited to share our project findings in this blog.

 

Lunar phase and urban badgers

For our project, we monitored a group of European badgers living in the grounds of Goldney Hall in Bristol. Badgers typically deposit their droppings into pits known as latrines. Latrines are often located near to setts or at strategic locations to act as territory markers. Many different species of wildlife have been found to change their behaviour in response to changing light levels, be it from an artificial light source or the moon. For example, the light from the moon might make it easier for animals to forage and hunt at night, but it also makes animals more visible to predators, prey and competitors alike. In the past, associations have been made between lunar phase and several aspects of badger behaviour and we wanted to investigate if any relationship existed with latrine use. As a group living in the centre of Bristol, we believed that high levels of light pollution would likely diminish any significant link with lunar phase in our study badgers.

First, we surveyed the site identifying the location of the sett and latrines, and using evidence of badger presence and geographical features we estimated the group's core territory. We set camera traps at their hinterland latrines (located around the sett) and boundary latrines (as the name suggests, located on the boundaries of their territory) to record footage of badgers visiting these latrines. As well as visits by badgers, the cameras recorded local cats, red foxes, birds, squirrels, a muntjac deer and helpfully every bout of high wind! From this footage, we recorded the frequency of latrine use over our 35-day sampling period.

When comparing our data on the frequency of latrine use with the lunar phase for each of the nights, a pattern emerged. The badgers in our group were using hinterland latrines significantly more in light moon phases (i.e. when visibility was higher), and the boundary latrines significantly more in dark phases.

There are a number of possible explanations for this association, but the correlational nature of our study makes proving causation difficult. Boundary marking is a territorial behaviour used to deter outsiders from other social groups. It’s possible that in dark phases the associated reduction in visibility increases the likelihood of invaders from other social groups, and so the local badgers compensate for this risk by boundary marking.

On the other side of the coin, a preference for using hinterland latrines (the latrines closest to the sett) when it is brighter could be explained by a reduction in activity due to a perceived higher risk when badgers are more visible. This theory is supported by a previous study that found badgers travelled shorter distances during low cloud cover and high lunar illumination (Cresswell & Harris, 1988). These two explanations essentially go hand in hand. If activity is lower during light phases due to conspicuousness, the risk of invasion is lower making need for boundary warning signals lower, and vice versa. It’s worth questioning why badgers need to show this cautious behaviour, as they have no current predators. However, evolutionarily that certainly isn’t the case, and they are victims of human persecution so being conspicuous at night is still risky.

Other less direct explanations, such as earthworm availability, could be at play. Earthworms are believed to spend less time at the soil surface during full moon phases (Michiels et al., 2001). This reduction in prey availability could drive a decrease in activity levels for our badgers. However, we ruled this explanation out as earthworms make up less than a quarter of the diet of urban badgers in Bristol (Harris, 1984) so their availability is unlikely to significantly influence their activity.

To fully understand this behaviour, further research spanning longer time periods and covering multiple lunar cycles is essential. Monitoring fine-scale badger movements using radio or GPS tracking would also improve the study and add more explanatory power to our observations.

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We have found the process of observing the badgers at Goldney for a couple months really enjoyable. As much as monitoring latrine use is, at times, not the most glamourous research, it’s been great getting to know these charismatic mammals and getting some hands-on research experience. It is also highly encouraging seeing a group of badgers thriving in such an urban setting.

I’d like to thank the Estates Department at Bristol University for allowing us to do research at this site, especially given the added complexity from Covid-19 restrictions. In addition, we would like to thank our project supervisor Prof. Andy Wakefield for the opportunity to do this research and for his help throughout.

References

Cresswell, W. and Harris, S., 1988. The effects of weather conditions on the movements and activity of badgers (Meles meles) in a suburban environment. Journal of Zoology, 216(1), pp.187-194. https://doi.org/10.1111/j.1469-7998.1988.tb02424.x 

Harris, S., 1984. Ecology of Urban badgers Meles meles: Distribution in Britain and habitat selection, persecution, food and damage in the city of Bristol. Biological Conservation, 28(4), pp.349-375. https://doi.org/10.1016/0006-3207(84)90041-7 

Michiels, N., 2001. Precopulatory mate assessment in relation to body size in the earthworm Lumbricus terrestris: avoidance of dangerous liaisons? Behavioral Ecology, 12(5), pp.612-618. https://doi.org/10.1093/beheco/12.5.612