Animals utilize their different sensory systems – smell, vision, and hearing, among others – to gather information about their environment. Further, the sensory modalities an animal uses to most effectively gather information vary between species. For instance, while humans seem to have a strong preference for their visual and auditory senses for everyday functioning, the same may not be true for rodent species, who may rely on their olfactory sense, or smell, to detect when predators are nearby. Still, whether it be in the context of using their sensory-acquired information to avoid a predator, to find the best possible mate to produce offspring with, or in many other contexts, sensory-acquired information across all animals influences their behavior to best serve their fitness: that is, their ability to survive and reproduce.
For a plethora of reasons – whether for the sake of lifestyle, mental health, ethics, cultural or religious relevance – different social groupings of humans have animal species that they deeply dislike. In these cases, humans have a long history of adjusting their own behavior to worsen the fitness of these animals, and will often take into consideration the important sensory modalities of these animals in doing so. For instance, in the case of mice, humans for many years have taken advantage of their keen sense of smell when designing mouse traps that utilize food as bait. By luring the mice via an attractive scent, humans take advantage of an animal’s sensory modality to reduce their fitness.
For many, voles, an herbivorous rodent species infamously known for chewing through the stems of young trees and plants, are considered annoying pests, or “yard-ruiners,” especially for homeowners with dreams of boasting their beautiful lawns. Consequently, yard-owners may have a distaste for a vole’s ability to reproduce and survive, and will take action to worsen vole survivability. Of course, there already exist effective preventative measures such as chemical repellents; however, for either ethical reasons or the health of their lawn, homeowners may consider pursuing alternative repellents, particularly those than interact with the strongest and most influential of the vole’s sensory modalities: their olfactory system. In the search for an effective repellent, researchers immediately turned to the smell output of the vole’s common predator: the cat.
Voles naturally exhibit a fear response to their feline predator; thus, Wu et al. (2020) investigate the influence of cat odor (specifically, a cat’s urine), upon the maternal behavior of a postpartum female Brant’s vole (Lasiopodomys brandtii), or one that has recently given birth to its offspring. In the study, researchers paired and mated adult female voles with male voles. Following mating, the female voles were separated into three separate 18-day olfaction conditions: (1) a cat smell condition, (2) a rabbit smell condition to examine for a potential effect of non-predatory smell stimuli, and (3) a control condition, where voles were exposed to distilled water. For 18 days in a row, the female vole was placed into a separate room for one hour, where they were exposed to a cotton ball soaked in 1ml of one of the three smell conditions (cat urine, rabbit urine, or water). At various day-points in the protocol, the researchers measured maternal behavior by placing female voles into the nests of their offspring, recording pup sniffing, pup licking, and nest building, among other behaviors. Afterward, they compared the averaged measurements of maternal care across all three groupings. Considering that cats prey on voles, as well as the previous research showing that voles display fear and defensive behavior to cat urine, the researchers hypothesized that exposure to cat urine would increase the fear in the female voles, reducing their ability to perform the aforementioned “maternal” behavior. Thus, they predicted to see reduced maternal behavior within the “cat urine” condition.
Interestingly, the researchers found reduced maternal care behavior within both the cat and rabbit urine groupings, both following after the first day of exposure and after prolonged (day 18) smell exposure; however, they found that the cat urine group had a stronger reduction in maternal behavior over the rabbit condition, particularly in the duration of pup licking and hovering above pups, and the percentage of pups physically picked up. Thus, the researchers’ prediction of observing reduced maternal behavior in the cat groupings was met, supporting their hypothesis of the cat stimuli increasing fear in the female voles.
As the researchers discuss, these results suggest that cat urine has a disruptive effect on the female vole’s maternal behavior, postulating that, when exposed to a smell stimulus that communicates danger and incites fear, a mother has to dedicate less time to maternal care and more to individual survival and vigilance. Voles, among many other mammals, require significant care during the early stages of their life. As a plethora of rodent developmental research suggests, lower-quality parental care of the offspring can have strong negative effects on their development and survival. Considering the results of this study, exposing voles to cat olfactory stimuli, specifically cat urine, presents a potentially effective way of reducing vole fitness.
Within the search for an effective vole repellent, Wu et al. (2020) present an effective argument in favor of cat urine, as their results that either upon short or long term exposure to the stimuli, vole mothers’ ability to provide their offspring with the necessary parental care is reduced, reducing in the overall survivability of their pups. Of course, given that this study was within a controlled experimental environment, further research would be required to see a more practical application, whether that be in the form of spreading out literal cat urine over a yard, or by simply investing in an outdoor cat for the protection of your yard. Further, Wu et al. (2020) focused on a particular species of vole, so research on Nonetheless, the results of the study suggest that having an outdoor cat for your yard may be a good first step towards treating your lawn’s vole problem.
Wu, R., Huang, Y., Liu, Y., Shen, Q., Han, Y., Yang, S., & Wei, W. (2020). Repeated predator odor exposure alters maternal behavior of postpartum Brandt’s voles and offspring’s locomotor activity. Behavioural processes, 177, 104143. https://doi.org/10.1016/j.beproc.2020.104143