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A meta-analysis was conducted with 62 mammalian species that changed their routine by 68% due to human disturbance. In São Paulo, mockingbirds start singing at dawn to avoid traffic noise

Human action on Earth is affecting animal behavior, and it’s more serious than imagined. According to a study developed by Berkeley University and published in Science magazine, the mere presence of human beings is leading other mammalian species to change their life habits and become predominantly nocturnal.

The global study gathered information about the daily activity patterns of 62 mammalian species across six continents. The result was that, on average, mammals were 1.36 times more nocturnal in response to human disturbance. This means that an animal that naturally splits its activity evenly between day and night increased its nighttime activity to 68% around people.

“Catastrophic losses in wildlife populations and habitats as a result of human activity are well documented, but the subtler ways in which we affect animal behavior are more difficult to detect and quantify,” study lead author Kaitlyn Gaynor said to Berkeley.

These data were collected by various approaches, including remotely triggered cameras, GPS and radio collars, and direct observation. For every species in each study site, the authors quantified the difference in animal nocturnality under low and high human disturbance. This finding was consistent across carnivore and herbivore species of all body sizes greater than 1 kg.

Why do animals change their habits?

According to the authors, they expected to find a trend towards increased wildlife nocturnality around people, but they were surprised by the consistency of the results around the world. As a conclusion, humans are seen by other mammals as predators – and this is independent of the nature of human activity, that is, whether or not humans impact their environment.

The pattern also held across different types of human disturbance, including activities such as hunting, hiking, mountain biking, and infrastructures such as roads, residential settlement, and agriculture.

“Animals responded strongly to all types of human disturbance, regardless of whether people actually posed a direct threat, suggesting that our presence alone is enough to disrupt their natural patterns of behavior,” the authors explained.

According to Justin Brashares, co-author and professor at Berkeley University, the positive side is that the fact that wildlife is adapting to avoid humans temporally could be viewed as a path for the coexistence of humans and wild animals on an increasingly crowded planet.

“However, animal activity patterns reflect millions of years of adaptation – it’s hard to believe we can simply squeeze nature into the dark half of each day and expect it to function and thrive,” Brashares considered.

The early mockingbird gets the word

In 2001, Brazilian biologist Sandro Von Matter noticed that mockingbirds who live in São Paulo start to sing earlier than in the countryside. In quieter places, birds shed their voice from 6 am, but in certain neighborhoods, birds sing until between 2 am and 3 am.

Von Matter’s curiosity has become the project Hora do Sabiá (The Mockingbird’s Time), which mapped the behavior of the bird far and wide Brazil with the help of 3,500 people who collaborated with the online platform.

Almost two decades after realizing the phenomenon, Sandro can tell that mockingbirds start singing earlier not only in São Paulo, but in all the great Brazilian cities. The reason for that is the intense noise caused by the traffic. Therefore, to perform their mating ritual, birds seek times when their song can be heard best.

“Changes in the physiology and behavior of animal species that inhabit cities may reflect pressures to which humans are also exposed. Assessing the impact of urbanization on these species is essential, not only for the conservation of biodiversity but also for the maintenance of our well-being and quality of life,” the biologist concludes.

Content published in August 16, 2018

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