Shh! I can’t hear the squirrels! Mongoose response to heterospecific alarm calls is inhibited by anthropogenic noise

A dwarf-mongoose. Credits: San Diego Zoo Animals

A casual walk through a neighborhood forest and one may notice the lush landscape, rich flora and fauna, and the plethora of dump trucks? Due to the recent advent of world-wide geo-construction and resource extraction, many forests are now littered with bulldozers and other large construction equipment, all used to exploit the land for a quick return on investment. This novel human activity has greatly increased not only human accessibility to previously untouched land, but also our knowledge of unknown territory. Although deforestation may have some positive aspects, one glaring negative effect is the associated noise and its impact on ecosystem activity.

Hunting behavior is a vital process that is common amongst all organisms. Equally as important, is the ability to evade predators and increase overall survivability. Interestingly, many organisms have adopted novel methods of predator evasion. Alarm calling, or the production of vocalizations to warn others of danger, is a key anti-predator strategy and has been adopted by a suite of organisms. This method allows a species to eavesdrop on heterospecific alarm calls with species with similar predators, inducing an efficient escape process. For example, the dwarf mongoose eavesdrops on the alarm calls of tree squirrels, and can promptly flee from danger. How has anthropogenic noise affected eavesdropping of heterospecific calls? A study by Morris-Drake et al., found that anthropogenic noise has the capacity to alter predator evasion behavior and consequently increase predator-prey interactions.

To investigate how anthropogenic noise affects alarm calling and eavesdropping on heterospecific calls, the study examined two separate cases: (1) play-back experiment 1 – to investigate the anti-predator responses to heterospecific alarm calls, and (2) play-back experiment 2 – to assess how road noise affects vigilance behavior and responses to heterospecific alarm calls. The first experiment attempts to understand which certain calls (conspecific – same species or heterospecific – different species) ellicit a response. The second experiment attempts to understand how anthropogenic noise affects the specific behavior and response towards heterospecific alarm calls.  The mongooses were subjected to a variety of play-back treatments and their responses and behavior were further recorded and analyzed.

Morris-Drake and her colleagues found that there was a response elicited by the mongooses when presented with a heterospecific call – an alarm call from a tree squirrel, a species that shares the same suite of predators. In addition, they found that there was a significant difference in the type of response elicited depending on the sound treatment. In the absence of anthropogenic noise, dwarf mongooses immediately flee when presented with a tree squirrel alarm call. The researchers found that when presented with road-noise, in addition to a tree squirrel alarm call, the dwarf mongooses exhibited a vigilance behavior (looking up and examining their surrounding) as opposed to fleeing. Furthermore, the proportion of time spent vigilant as well as the vigilance scan rate were also significantly affected by the different sound treatments.

A: The inverse relationship between the number of individual responses and the presence of road noise. B: An increase in vigilant time during the presence of road noise. C: An increase in vigilance scan rate during the presence of road noise. D: An increase in “looked up” responses in the presence of road noise as opposed to “fleeing” responses. Credits: Amy Morris-Drake

What significance does this experiment offer the general sensory ecology community? The results of the experiment indicate a substantial effect of anthropogenic noise on predator evasion behavior. During the presence of road-noise, dwarf mongooses spend considerably more time scanning their environment as opposed to fleeing a predator site. This behavior greatly increases the probability of predator-prey interactions and decreases overall survivability. On a more general scale, the results did shed light on the consequences of anthropogenic noise on overall community structure and its role in anti-predator responses. The study also provides an opportunity for further research on determining causal links between anthropogenic noise and organism population consequences, as well as fitness consequences for individuals in the presence of road-noise.


Morris-Drake, Amy., Bracken, Anna M., Kern, Julie M., Radford, Andrew N. 2017. “Anthropogenic noise alters dwarf mongoose responses to heterospecific alarm calls.” Environmental Pollution, vol. 223, pp. 476-483.

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