Monkeys raise a stink in response to human noise pollution - study

Monkeys including Pied tamarins (Saguinus bicolor) show their displeasure when exposed to human noise pollution by making loud vocal calls and releasing foul odors. Perhaps humans exposed to their neighbors’ racket may be jealous of them.

Researchers at Universidade Federal do Amazonas in Brazil and Anglia Ruskin University (ARU) in the UK found that monkeys increase their use of scent markings and are the first to investigate how primates change their communication strategies in response to upsetting noise. 

The pied tamarin has an extremely narrow geographic range in central Brazil, much of which now lies within the city of Manaus. The city’s expansion has restricted individual groups to small patches of forest, surrounded by noisy urban environments, and the species is considered critically endangered by the International Union for Conservation of Nature (IUCN).

The new study investigated the behavior of nine separate groups of wild pied tamarins by using radio tracking to follow each group for 10 days. It was published in the journal Ethology Ecology & Evolution under the title “Do pied tamarins increase scent-marking in response to urban noise?”

Noise pollution caused by humans

Within each area visited, the most common source of anthropogenic noise was road traffic, although there was also noise pollution caused by aircraft, park visitors, and even military activity. Being able to communicate with other groups is vital for the health and ultimately the survival of a species. Pied tamarins use several types of scent marking which have different functions, including passing on reproductive and territorial information.

The team researchers found that the frequency of scent marking directly increased in line with noise decibel levels. The results suggest that scent marking is being used more frequently as the pied tamarins’ vocal communication becomes less effective due to the impacts of human noise.

The biologist and lead author Dr. Tainara Sobroza of Brazil said: “Many species depend on acoustic signals to communicate with other members of the same species about essential information such as foraging, mate attraction, predators, and territorial defense. Pied tamarins produce long calls that are used for group cohesion, intergroup communication and to mark their territory. Long calls are especially important in fragmented forests which is the case in Manaus, as the urban landscape encroaches further into the pied tamarins’ territory. Our research indicates that communication is being impacted by urbanization as the occurrence of scent marking is increasing directly in response to increased noise levels.”

The tamarins didn’t reduce the number of long calls in response to anthropogenic noise. Although the occurrence of scent markings increases with noise levels, they found that scent-marking occurrence increased with noise amplitude. Thus, their results don’t suggest a complete shift between channels but complementation of information, where scent marking may compensate for the impacts of anthropogenic noise on the acoustic channel. This is an interesting result from a conservation perspective as pied tamarins may be capable of coping with city noise to communicate with conspecifics, a key tenet of species survival.

Co-author and evolutionary biologist at ARU Dr. Jacob Dunn said that “humans have contributed many additional stimuli to the soundscapes that animals have evolved to deal with, and anthropogenic noise is increasingly drowning out natural sounds. The increased use of scent marking by pied tamarins is likely to be a flexible response towards this environmental change. This is an interesting result from a conservation perspective as it shows pied tamarins are adapting their behavior in response to city noise.”

An advantage of scent marking over vocal communication is that it allows information to be passed on over a number of days. However, unlike vocal calls, scent markings are not an effective way of communicating over long distances. As the pied tamarins’ range is becoming more fragmented and groups are becoming more isolated, this could potentially have a detrimental impact on a species that is already critically endangered, the authors concluded.