Farmland is tricky territory for wildlife and scientists alike. Oceans of corn or soybeans doused with herbicides and pesticides typically make for poor habitat. “No Trespassing” signs and scattered slivers of untamed nature are a logistical headache for researchers trying to gather enough data to see meaningful patterns.
But Adam Dixon, a conservation scientist for the World Wildlife Fund, found how to make headway in this difficult environment, harnessing recent technological advances to get a closer look at how birds in the heart of U.S. farm country are faring.
“What was impressive about Adam’s investigation was his willingness to employ novel technology and ideas to overcome what has historically been an absolute challenge in surveying working landscapes,” said Matthew Baker, an ecologist at the University of Maryland, Baltimore County, where Dixon earned a PhD while doing the research.
The tools were tiny, cheap audio recorders, sound processing software, satellite imagery, and enough old-fashioned charm to win the cooperation of some Iowa farmers. “It’s difficult but not impossible to work on private lands,” says Dixon, who grew up in the Midwest. “You just need to build trust and relationships.”
To explore the ways birds use little pockets of un-plowed land, Dixon approached farmland owners with a request: Could they help him install microphone-equipped circuit boards smaller than a deck of cards in pockets of greenery at the edges of their fields? All told, he was able to retrieve data from 44 recorders, known as AudioMoths, at locations across the state.
During the summer of 2019, each device provided at least 95 1-minute recordings collected around sunrise, when many birds are most vocal. Using a computer program designed to comb through audio files in search of bird songs, Dixon heard 51 different bird species in the recordings. As many as 26 species were captured at a single location.
When Dixon compared the number of bird species to satellite imagery of the different plots, he found a strong correlation between the percentage of surrounding land that wasn’t farmed, and the diversity of birds. For every 10% increase in the percentage of land covered in plants that weren’t crops such as corns and soybeans, the richness of bird species increased by around 8%, the scientists reported earlier this year in the journal Ecological Applications.
For Erle Ellis, a University of Maryland landscape ecologist who has spent years studying how human activity such as farming transforms ecosystems, the new findings point to the possibility that wildlife can find homes even in such homogenized places. “Agriculture covers more of this planet than protected areas,” said Ellis. The research “confirms that even some of the most intensively managed agricultural landscapes on Earth can sustain significant biodiversity.”
But it’s not all good news. The study found that the birds that benefited most from these habitats were ones that only sporadically use grassland habitats, such as robins and house wrens. There was no evidence that in increase in vegetation alongside fields was linked to greater varieties of grassland-dependent species, such as the bobolink, eastern meadowlark or upland sandpiper.
“Agricultural habitats are good for birds in general,” said Dixon. “But when you look at grassland birds specifically, either there’s not enough habitat or the habitat characteristics aren’t good.”
Dixon et. al. “Passive monitoring of avian habitat on working lands.” Ecological Applications. April 24, 2023.