Since 1970, the bird populations in North America have dropped by around 3 billion birds – nearly a third. This is according to a research study published recently in the journal Science. The most severe drop has been in grassland species populations, which have declined by around half in the past 50 years. The trend is not idiosyncratic to North America, according to the study’s authors. Across the world, fewer birds are seen flying through the skies and turning grasslands and meadows into nesting grounds.

The researchers gleaned these trends primarily by tapping into government data collected by the United States Geological Survey (USGS) and the Canadian Wildlife Service. The North American Breeding Bird Survey consists of thousands of well-trained birdwatchers who trek out to randomly selected sites across the U.S. and Canada during breeding months to identify and count the number of hundreds of bird species. The government’s monitoring effort began in the late ’60s in response to growing anxiety about our poor understanding of how pesticides affect our country’s wildlife.

The study’s authors also used a network of radar monitoring stations set up by the National Weather Service (NWS) to estimate changes in the size of bird migrations from 2007-2017. The network consists of around 140 radar sites scattered throughout the U.S. and is normally used to track the size and movement of weather events. Researchers perusing data from the NWS’s network can easily distinguish between moving clouds and the much more intentional, speedier movement of bird flocks. The data also showed a decline in number of birds, corroborating the trends that the scientists observed in the decades-long ground surveys.

There are a couple nuances to the findings. One is that the severe drop of billions of birds is a net loss. Though the number of birds in basically all habitats have gone down, wetlands are an exception. The authors found a slight increase of just over 10% since 1970. Though the survey data and radar networks can’t tell us why any of these trends are happening, scientists have proposed that wetland birds rebounded in response to efforts to conserve wetlands and tight regulations of pesticides such as the infamous DDT – the same pesticides that spurred the USGS in the ’60s to start surveying birds in the first place. Similarly, scientists speculate drastic loss of grasslands and other habitats could be a major reason for decline of birds in all other habitats.

Another key point about these findings is that this is not just a list of endangered birds facing further peril. The recent declines are predominantly in common bird populations such as swallows and sparrows. That is perhaps cause for hope. These common birds are down, but they’re certainly not out. Since their populations are still quite large, the bird species could plausibly rebound, if proper action is taken. At the same time, the once common passenger pigeon’s shocking extinction demonstrates how quickly a common bird can disappear when nature is sufficiently gripped by humanity’s influence.

Managing Correspondent: Jordan Wilkerson

Original Science Article: Decline of the North American avifauna

Image Credit: Flickr

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