Spotlight on foraging behaviour of nocturnal rodents

What wakes you up in the morning? Is it your alarm clock? Is it the clattering of your housemate in the kitchen? Is it the smell of coffee? While these experiences happen like clockwork, for many organisms it is not sound or smell that wakes them up but the sun. Those first dawn beams of light breaking the horizon, and the last glimmers in the night. For billions of years all of life has relied on this rhythm. Their very metabolism reliant on the cues provided by the great ball of fire in the sky.

We humans have changed our own schedules with alarm clocks and coffee, but our influence does not end at our own lives. The lights we use to illuminate our nights, make roads safe to drive and advertise the newest brand of cereal have endless consequences for the creatures around us. Artificial light at night and light pollution are affecting all living organisms. Light bulbs have been shown to disorient nesting turtles from reaching the sea and cause bird collisions. Importantly light pollution disrupts our biological clock, the internal chemical time-keeping device perhaps common to all living things.

 

 

Night dwelling prey animals have been some of the most effected groups of animals. These creatures have adapted to foraging and being active under the cover of darkness to escape from predators. The increased visibility from human light sources poses a critical risk for these animals as it can make them easier to spot by predators. This risk creates a powerful adaptive force, demanding the nocturnal animals change or perish.

Fu-Shun Zhang and colleagues set out to understand these changes. They studied the foraging patterns of Mongolian five-toed jerboa (Allactaga sibirica), a common nocturnal rodent. It is found in the grasslands of China, especially in Inner Mongolia. It uses the grass to escape predation from owls, snakes and foxes while looking for seeds during the night.

The jerboa were placed in enclosers that simulated their natural conditions and contained small lamppost-like structures that the researchers could turn on and off. Near to the lampposts the researchers placed buckets with equal number of seeds hidden among sand.  They observed the rodent’s behaviour in different light conditions. They measured the number of seeds left in the bucket after the night and how long the jerboa spent foraging in the buckets.

The researchers found that the jerboa who foraged in artificially lit conditions spent far less time foraging and left more seeds in the bucket than those who forgaed in the dark. The animals under artificial light also performed more vigilance behaviour, i.e. time spent looking for predators. However, the jerboa who were in the lit conditions were more efficient at finding the seeds, i.e. they found the first three seeds in less time than the ones in the dark.

The results of this paper show that artificial light at night can have several effects on the behaviour of animals. These rodents were generally negatively affected by the light, eating less than their dark counterparts. However, the researchers theorised that because the light allowed them to see better they were able to find seeds faster. What this means for the evolution of this tiny mammal would require generational studies; however, it could be possible that artificial light at night places adaptive pressure on faster moving, more vigilant animals. This is similar to other research into urban-adapted animals who show higher breath rate and faster foraging behaviour.

This study and research like it is only beginning to untangle the effects our urban innovations are having on the world around us. Artificial light is present all over the globe, with areas in Europe being most affected. With the increase in human activity and urbanisation, the ecological threat of light pollution continues to increase. While our bedside lamp and traffic lights seem normal to us, we have to remember the ecological threat artificial light use poses to the rest of the planet, a threat the full implications of which are yet unknown.

 

Read the studies

Kyba, C. C. M., Kuester, T., Sánchez De Miguel, A., Baugh, K., Jechow, A., Hölker, F., Bennie, J., Elvidge, C. D., Gaston, K. J., & Guanter, L. (2017). Artificially lit surface of Earth at night increasing in radiance and extent. https://www.science.org

Ryan, A. M., & Partan, S. R. (2014). Urban Wildlife Behavior. In Urban Wildlife (pp. 149–173). Springer US. https://doi.org/10.1007/978-1-4899-7500-3_9

Zhang, F.-S., Wang, Y., Wu, K., Xu, W.-Y., Wu, J., Liu, J.-Y., Wang, X.-Y., & Shuai, L.-Y. (2020). Effects of artificial light at night on foraging behavior and vigilance in a nocturnal rodent. Science of The Total Environment, 724, 138271. https://doi.org/10.1016/j.scitotenv.2020.138271