As the group ascended the nearest tall-standing structure, they congregated at its summit and turned to face the sky as it darkened. Mothers clutched their young, fathers sat still and gazed in wonderment and an orphan infant, standing tall, gestured upward as the Sun and Moon eclipsed far above the cold woodland surroundings of the Yerkes National Primate Research Centre.
Back in 1984, this collection of chimpanzees was among the first mammals to be observed and analysed for their responses to lunar events. The researchers, Jane Branch and Deborah Gust, described the group’s behaviours that coincided with the solar eclipse as “atypical”, noting they were not replicated during previous and subsequent sunsets and sunrises.
The research highlights the shared curiosity of cosmic events between us and our primate cousins but, more importantly: that variations in lunar activity, and not just the position of the Earth relative to the Sun, can affect animal behaviour.
The study of the effects of the Moon on animals – much like the effects of the orbital body on the Earth’s tides – would continue to create waves within the studies of animal ecology and behaviour from this point in time.
Wane, wax
While our days are neatly packaged into 24-hour-long increments, or periods relative to the position of the Sun in the sky (morning, noon, dusk, evening and so on), the lunar cycle follows an approximately 24.8-hour rotation. This mismatch between the Earth’s rotation upon its axis and the time it takes for the Moon to circle our globe is causative for many natural phenomena (including the tides and magnetic fields), as well as the differing phases of the Moon’s illumination.
In the animal world, these cycles in the relative positioning or illumination from the Sun and the Moon serve as time cues for behaviours such as the moonlit serenades of the willie wagtail, the lunar navigation of the Australian bull ant or annual mass spawning events from the Great Barrier Reef coral.
These conspicuous or large-scale behaviours are well-studied, but what is yet to be described are the nuanced variations in animal activity during the night: changes in predation strategy, shifts in foraging locations or variations in travelling within habitat boundaries.
This knowledge gap comes down to the observational nature of this science, and how nocturnal animals can be extremely difficult to capture or observe in a natural setting.
The whole of the Moon
“I think [the difficulty with studying nighttime animal behaviours] is just the fact that people prefer to work in daylight hours.”
Dr Euan Ritchie, Professor of Wildlife Ecology and Conservation at Deakin University, candidly jokes about his experiences studying the behaviour and ecology of primarily nocturnal species.
He too is part of this new wave of biological research, co-authoring a seminal study about the responses of Australian fauna to lunar illumination in the semi-natural environment of the Mount Rothwell Conservation Reserve in rural Victoria.
Australian researchers in this field face a unique dilemma: the majority of Australian mammals are primarily active at nighttime and therefore more difficult to observe.
Now nearly 40 years after the chimpanzee study, lunar animal research is receiving the technological and methodological breakthroughs necessary for the next wave of findings.
“We now have technology like camera traps as an example and things like drones as well, thermal imaging that allow us to get a much deeper understanding of animals than we did in the past.”
Advances in remote camera technologies have finally granted researchers unprecedented access to observe animal behaviour in the wild and in real-time, but most importantly without affecting any outcomes because of their presence.
As our discussion revolves around how this study can contribute to the greater understanding of animal behaviour, he notes that understanding the Moon as a variable in animal presence or absence will also help ecological studies and conservation efforts.
“If you’re putting out traps of some description… and you’re not factoring in moonlight, then you may not have a picture of how that influences trapping success.”
He adds that his group also established wind in conjunction with natural light as an important factor in nighttime animal activity.
“If it’s dark, but also super windy, it might make it really hard for you to get a direction on where a scent is coming from, and this could be a predator’s scent. So, on a really, really windy night, animals also tend to be quite often very low in their activity.”
The bigger picture
While research on our mammals is important, Australian species only make up roughly 7 per cent of the global total, leaving a large research gap.
An ambitious overseas project has sought to utilise these novel remote camera technologies across several continents to ascertain the greater patterns of mammalian activity in response to lunar illumination.
The newly published article in Open Biology was headed by Professor Douglas Sheil from Wageningen University in conjunction with collaborators across North and South America, Africa and Eurasia. By setting up remote camera traps in tropical forests, they recorded the daily activity patterns of 86 different mammalian species. This study was the first and largest of its kind, and sought to better understand different species’ attraction to – or avoidance of – lunar illumination and their activity during different lunar phases (for example, full moons).
The goal of the study – like many of the newest studies surrounding lunar illumination and animal activity – was to describe animal behaviours in nighttime conditions, and to create predictive models of animal resilience in the face of increasing man-made light pollution and habitat degradation.
The findings shed light on tropical forest ecosystems: only 15 species showed disrupted activity because of lunar illumination (12 species decreased activity during full moons while three species displayed increased activity) but half of all observed species (43) shifted their daily activity patterns during each of the lunar phases. Some became more active during the night depending on varying degrees of lunar illumination (i.e. full moon vs half-moon), some altered their regular activity patterns at night, and many species did both.
Filling in the gaps
Large-scale studies such as these are incredibly important in outlining broader patterns in fields of research where literature is otherwise sparse. However, there can be many factors unaccounted for in their observations. Professor Ritchie notes several pros and cons of the large-scale methodology.
“I think the beauty of these really big studies is you can make some general statements about what’s happening with a large number of species.
“The downside, of course, is that you may lose some of that location-specific information that would allow you to understand why it is that an animal might not have a response [to lunar illumination] …Maybe the habitat is completely different in that area.”
What these studies do achieve, despite potential shortfalls in their methods, is the catalysis of conversation within scientific communities. Discussions surrounding how the study could be better replicated next or which gaps in knowledge they have created will no doubt be the genesis of future research.
A tail of two cities
When discussing the potential applications of this research, Professor Ritchie notes the efforts of urban ecologists in outlining species that will adapt well to the inevitable urbanisation of many natural landscapes, including artificial light pollution.
“You could make the argument that if you’re not bothered by lots of moonlight then maybe you’re predisposed to being able to cope to artificial light. The question would be though, what other changes are associated with artificial light?”
We often think of the relationship between wild animals and urban environments as being less-than-harmonious (bears aren’t often too polite when entering backyards), but urban ecologists argue that the continued land clearance and urban development will inevitably lead to more species looking for a suburban or inner-city lifestyle.
This usually means drastic changes to their activity patterns, especially when factoring in how it relates to human activity.
Take the European red fox as an example.
“[They] are one of the most widely distributed predators in the world, and are invasive in many parts [including Australia],” explains Professor Ritchie.
“There’s huge amounts of light pollution [in most of these areas], but you typically don’t see foxes until you drive around late at night when most people have gone to bed.”
What research such as this will do is help identify the species less likely to cope with these upcoming challenges and target them for conservation and relocation efforts.
Species such as the cosmopolitan pigeon or fox won’t need any aid, given they famously adapt to most environments they find themselves in. However, some species – such as the lunar phobic rodent and armadillo species outlined in this study – may need some assistance.
What’s next?
With the bigger picture starting to take shape in this research landscape, it’s up to scientists to start filling in the knowledge gaps. From here, the task is to hone in on individual species identified from studies such as this and ensure the correlations between lunar illumination and activity hold true for a variety of scenarios.
Important factors such as effects on breeding and migratory patterns, seasonality and communication are among the most important to characterise, as well as how consistent these effects are across varying environments.
For those of us Down Under, where a large proportion of our country is devoid of consistent tree cover, questions will no doubt arise as to whether our species act differently to those of tropical jungles when dealing with lunar illumination.
But until then, we should do our best to welcome our four-legged neighbours.
