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Small Amazonian monkey must adapt to urban noiseGummybone / Getty ImagesIn the thick of the urban hustle and bustle, constantly buzzing with traffic sounds, children rehearsing Christmas carols at school, and military orders bellowing from the barracks, small monkeys in Manaus attempt to communicate with each other. The pied tamarin (Saguinus bicolor) exists only in the Manaus region of Amazonas and emits high-pitched screeches to assert its presence. “Our hypothesis was that they would change communication methods in the noisiest areas,” says biologist Tainara Sobroza, a substitute professor at the Federal University of Amazonas (UFAM).
During her doctoral studies at the National Institute of Amazonian Research (INPA), Sobroza followed a group of pied tamarins in swathes of urban forest to see if they would sideline their screeches in favor of a communication style less muffled by the city. She discovered that they continued producing vocalizations but also went on to use chemical communication more frequently, scent-marking trees. “They have glands in the genital, perianal, and sternum regions, and they rub against trees to leave a mark,” describes Sobroza, who published the findings in September’s issue of Ethology Ecology & Evolution.
Nine groups were studied in forest fragments ranging in size from 24 hectares (ha) to 730 ha. The latter, on the UFAM campus, “in the Atlantic Forest would be considered continuous forest,” compares Sobroza. In the Amazon region, however, it is part of the urban area.
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It is difficult to see exactly what these primates are doing so high up in the trees, as they are the size of squirrels and weigh no more than 600 grams. They live in matriarchal groups of up to 13 individuals. “Only one female reproduces and everyone in the group helps take care of the offspring, usually a pair of twins in each birth,” explains the researcher, who would use binoculars to see when one of them rubbed the back of its body against a branch or vocalized. The noisier the area, the more frequent the behavior.
The observations took place over the course of a year, with each group being followed for 10 consecutive days, from 6 a.m. to 5 p.m. To find the tamarins, Sobroza’s team first had to carry out a familiarization process so that they could catch the monkeys in traps installed high up in the trees. The traps consisted of barred crates that do not harm the animals. “This process took up to four months, which is why we were only able to follow nine groups,” says Sobroza. Catching them was necessary in order to place collars with radio transmitters. Without these, they would likely be unable to find the same group the next day.
One interpretation of complementary communication through alternative channels—or multimodal communication, in ethology jargon—is that it serves to attract attention. “The tamarins are more likely to perceive the vocalization when they smell the scent,” says the biologist. According to her, this type of study had not been carried out on monkeys in the wild because of how difficult they are to observe. A similar example would be the little Brazilian torrent frog: when males gesture with their fingers in addition to vocal communication, it is a strong call to fight.
Primatologist Júlio César Bicca-Marques, of the Pontifical Catholic University of Rio Grande do Sul (PUC-RS), cannot recall any similar studies on communication in nature. This type of behavior is not his research focus, but his group has studied other aspects of monkeys in urban contexts. A few years ago, he wrote a review for the abstract of the book The International Encyclopedia of Primatology (John Wiley and Sons, 2017). “One of the effects of urbanization reported in the study is that monkeys lose crucial information about their natural environment. Such is the case of the bonnet macaques (Macaca radiata), which live in the city and do not recognize sounds emitted by predators.
Southern howler monkeys
But the most striking effect of adaptation to cities is the shift in food availability, which can cause changes in the movement patterns of animals no longer seeking out their usual food sources. Food-based interactions between humans and monkeys can lead to some species being considered pests in cities. These interactions can also threaten the animals’ health. In São Francisco de Assis, a small town in central Rio Grande do Sul, PUC-RS master’s student Isadora Alves de Lima recently observed black howler monkeys (Alouatta caraya) receiving barbecue leftovers from restaurant employees and patrons, according to an article published in October in Primates. This is surprising because this species is known to eat leaves and fruit. “We have already seen howler monkeys eating eggs and we have received reports of birds being eaten, but nothing close to grilled meat,” says the primatologist. Her group collected feces samples to study how this change in diet affects the microbiota—intestinal tract bacteria, responsible for part of the digestion process. In the future, she hopes to evaluate the effects of this new diet on the animals’ health.
Regarding vocalizations in this environment, Bicca-Marques reports having heard fewer howls, the farthest-reaching howler monkey calls. “When a single group lives on a block, it doesn’t make as much sense to exert energy on territorial vocalizations,” he explains.
In his review for the primatology encyclopedia, he highlighted the potential for these urban populations to offer monkey-watching experiences as a way to encourage people’s connection with nature and respect for wildlife. This is the case of the black-tufted marmoset (Callithrix penicillata), which became the ecological symbol of Belo Horizonte, Minas Gerais State, in 1992, and the pied tamarin, considered the mascot of Manaus since 2015. “Despite all of the efforts made by scientists and conservationists, little (if anything) has changed to benefit the pied tamarin since then,” he laments in the text.
Scientific articles
SOBROZA, T. V. et al. Do pied tamarins increase scent-marking in response to urban noise? Ethology Ecology & Evolution. Online. Sept. 20, 2023.
BICCA-MARQUES, J. C. Urbanization (and primate conservation). The international encyclopedia of primatology (Augustín Fuentes, org.). John Wiley and Sons. 2017.
LIMA, I. A. & BICCA-MARQUES, J. C. Opportunistic meat-eating by urban folivorous-frugivorous monkeys. Primates. Online. Oct. 20, 2023.
