Humans do not have to cut down trees or build roads to disrupt wildlife. Their mere presence in a landscape can change how wild animals use space and resources, according to a new analysis of human and animal movements during the Covid-19 pandemic.

The researchers paired GPS tracking data from 37 species of wild birds and mammals with cellphone location data across the United States. For two-thirds of those species, the presence of humans appeared to affect how much geographic space the animals used or how varied their environments were, the researchers found.

But these human impacts were complex, and in many cases, the effects of human presence were intertwined with the effects of landscape modification. For example, when humans disappeared, elk and mule deer expanded their land use. But these effects were more pronounced in rural or undeveloped locations than in highly developed ones like cities.

“We really can’t understand the full picture without information on both of these factors,” said Ruth Oliver, an ecologist at the University of California, Santa Barbara, and a co-author of the new paper.

Human activity also had different effects on different species. “The ravens in Yellowstone are behaving really differently than white-tailed deer on Staten Island,” said Scott Yanco, a research ecologist at Smithsonian’s National Zoo and Conservation Biology Institute and a co-author of the study.

The research, which was published in the journal Science on Thursday, was conducted by a large international team as part of the Covid-19 Bio-Logging Initiative, which has been studying how animals responded to the pandemic-related slowdown in human activity known as the “anthropause.”