Habitats of North American birds, especially wintering grounds in Central America, face their greatest threat from human activities, according to a recent study published in the journal Global Change Biology.

Birds’ wintering, or non-breeding, grounds are important because they spend about 60 percent of the year there, according to lead author Frank La Sorte, a research associate at the Cornell Lab of Ornithology. Their breeding habitats, where they spend about 40 percent of their time, are typically located in forest environments of the eastern United States and Canada.

A database called eBird that lets volunteers enter bird observations from all over the world inspired La Sorte to begin the study.

“This unique source of information allowed us to document species’ associations with climate and land-use change during all phases of their annual cycle,” said La Sorte, part of an international research team.

Over the course of a year, the study looked beyond just the birds’ breeding seasons in North America. It measured the combined impact of climate change and land-use change, as more forests are being turned into cropland or grassland, in their wintering grounds in Central America.

The authors concluded that loss of wintering habitat will be worsened by long-term effects of climate change, such as warmer temperatures and less rain in non-breeding grounds.

In order to make these predictions, the authors ran scenarios based off of observations contributed by volunteers on the eBird database of 21 different species — most of them warblers, vireos, and flycatchers — from 2004 to 2014 to determine where the species were found during the year. They then added in climate change projections and habitat data to draw their conclusions.

“Human activities are placing pressure on bird populations from many different angles at varying intensities,” said La Sorte. “Birds are responding with tools designed to function under gradual environmental change — but how effective this will be under rapid change occurring from many different sources is not well understood.”

The authors believe that the best way to protect Central American land from experiencing more habitat loss is for conservation groups to collaborate with agencies that have authority in those countries.