Delayed mowing benefits birds

Many North American bird populations have been disappearing, with no groups decreasing more quickly than birds that nest in grasslands.

“It’s definitely the case here in New York state,” said David Bonter, senior extension associate in the Cornell Lab of Ornithology. Economic forces, changes in farm practices and reforestation have decreased the open grasslands that support birds.

“In Tompkins County, much of the open areas around here are owned and managed by Cornell University,” Bonter said. “So if we’re going to do anything to help the grassland bird populations, at home is a good place to start.”

Bonter and stakeholders from the Lab of Ornithology, Cornell Botanic Gardens and other Cornell land stewards started the project in 2022. A year later, they found grassland bird populations decreased in areas mowed in June compared with Dunlop Meadow Natural Area, a 58-acre area Cornell Botanic Gardens manages specifically to support grassland birds.

This year, the Cornell University Ruminant Center (CURC), which feeds its 1,100 dairy cows and calves with hay from Cornell fields, delayed mowing a 17.5-acre hayfield to expand the study. 

Tabares Erices and David Benvent ’25, both environment and sustainability majors in CALS, rose before dawn to search for and monitor nests in the unmowed field and the adjacent mowed fields throughout the nesting season, taking breaks to wring the morning dew out of their socks. 

Fewer nests made it all the way to fledging in the mowed fields, where Bonter hadn’t expected to see any reproductive success.

But they found savannah sparrows build their nests very close to the ground, giving them a chance to survive being mowed over.

“A pleasant surprise was that some savannah sparrows can survive the intensive mowing regime,” Bonter said. “If it’s enough to sustain populations, who knows. But it wasn’t all tragic.”

The birds need approximately three weeks from nest building to fledging. Delaying mowing a few weeks is a slam dunk for helping grassland birds get off a clutch of eggs, Bonter said, but farmers are working with very small financial margins, and just a week of delay can make a big difference.

“There is acreage that we set aside every year to mow later for lower-quality hay or later-cut hay,” said Greg Johnson, director of operations at CURC, based in Harford, New York.

“Instead of setting aside 10 acres, maybe if we set aside 20 acres, that would be more beneficial? Or maybe if we mowed it a week later? What would that look like?” Johnson said. “What does this delayed harvest do for both a bird population and then for our yields? What is the critical threshold?”

The Lab of Ornithology compensated CURC $2,050 to offset the loss of hay that would have been harvested from the parcel set aside for this study.

“Sometimes it does take an economic carrot” to get a practice started, Johnson said. “I think there are ways to tip the scale to encourage new practices.”

“Farmers do not like mowing down grassland birds,” Bonter said. “I think if they knew that following certain practices would be effective in helping grassland birds, while at the same time having limited impact on the economics of the situation, that nine out of 10 farmers would choose to change what they’re doing.”

Native grasses support the environment

The grass itself is the subject of another project to understand how to grow a turfgrass lawn with grasses that thrive in the region – and use less fertilizer, pesticides and water.

Cornell Botanic Gardens is expanding the native grass lawn in the Mundy Wildflower Garden, as the third phase of a project that started in 2009.

“It is an alternative to traditional turfgrass lawns,” said Todd Bittner, director of natural areas for the Cornell Botanic Gardens. “We want it to be aesthetic. We want it to be able to tolerate moderate trampling. We want it to require no watering post-establishment, no pesticide or fertilizer inputs, to consist of 85% native species and to be more beneficial for wildlife.”

Commercially available turfgrass seed typically comprises grass varieties native to southern states. They need richer soil, a lot of water and can’t out-compete weeds. 

“The idea is that 2% of the U.S. land base – the size of Wisconsin – is turfgrass lawns, and they have a larger environmental footprint than agriculture,” Bittner said. “The typical homeowner uses 10 times the amount of pesticides and fertilizers on their turfgrass lawn as the next highest agricultural crop. The American lawn takes up an area three times larger than that of any other irrigated crop in the country.”

The native grass lawn expansion builds upon early phases by incorporating native species that grew in the native lawn spontaneously. “They came in from the perimeter of the wildflower garden, and they thrived in it,” Bittner said. “And so we thought, well, let’s put those in intentionally.”

Another benefit they’ve discovered: It requires much less mowing.

‘Tall Grass, Small Gas’ fosters a living lab on Libe Slope

A desire to mow less inspired the Tall Grass, Small Gas initiative on campus in 2009. Since then, the Cornell Grounds Department has decreased the frequency of mowing hillsides and difficult-to-reach areas. 

Approximately 35 acres are mowed just once a year, saving around 9,700 pounds of CO2 emissions annually. The shift has also nearly eliminated nitrogen fertilizer, which emits nitrous oxide, a particularly damaging greenhouse gas.

Credit: Jessica Suarez/Cornell Lab of Ornithology

The initiative is part of Cornell’s Climate Action Plan to reduce emissions and reach its goal of carbon neutrality by 2035.

And now an iconic Tall Grass, Small Gas area on Libe Slope is doing double duty as a research site.

Kyle Wickings, associate professor of entomology at Cornell AgriTech, wondered if reduced mowing could improve the biodiversity of organisms that live in the soil and how they cycle carbon. So he integrated Libe Slope into a larger study researchers in his lab are undertaking at AgriTech in Geneva, New York.

The study contrasts annual mowing on Libe Slope and the regular weekly mowed areas just adjacent to it. Similar plots at AgriTech replicate the weekly and yearly mowing and include plots that are mowed every other week and every four weeks. Now in its second year, the three-year study is funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

So far they’ve found grasses that are mowed every two weeks seem to be driving the highest biodiversity. 

Below-ground biodiversity enables a grassland to function. “Whether it’s fertility of soil, capture and storage of carbon and, in some cases, the suppression of pests and pathogens,” Wickings said, “that community of microbes and invertebrates is really what’s driving that. Greater diversity within those communities is what drives resilience in those ecological services.”

Wickings’ team chose mowing as its variable for the study because it’s applicable to all managed grass systems – from homeowners’ lawns to golf courses and hayfields. “It’s low hanging fruit for something we can affect with management,” he said.

Carbon sinks and sequestration

Grasslands could also offer a way to sequester carbon, according to Cornell’s Carbon Sinks and Sequestration Working Group, which aims to reduce the Ithaca campus’ carbon emissions to net zero by 2035, along with achieving other goals set in Cornell’s Climate Action Plan.

The group is evaluating how much carbon could be sequestered – and how much it would cost – to convert underutilized Cornell lands to grasslands and forest.

This work complements and bolsters Cornell AES’ plans to transition some of the 2,600 acres of land it manages to forest and grasslands in the coming years, with funding from the New York State Department of Agriculture and Markets earmarked to facilitate climate resilience and demonstrate climate smart, adaptive field infrastructure. Other Cornell-owned areas across the state are also under consideration for land-use changes.

Transitioning suitable areas to grassland provides a big ecological bang for the buck, because grasslands establish quickly and provide important habitat for native species. It’s also easy to pivot grasslands to other uses, said Schrader, the working group’s co-chair.

The working group has been asking questions like: Can we manage spaces in a different way to meet Cornell’s carbon goals? Could we consider carbon management, watershed management, enhanced engagement opportunities and ecological connectivity? “How can we weave those four principles into the fabric of working landscapes – at Cornell and across New York and beyond?” Schrader said.

And grasslands have a powerful capacity to sequester carbon, so understanding them could be key in the fight against climate change, said Rebecca Schneider, associate professor of natural resources (CALS) who has worked on water resource management and grassland restoration projects around the world.

About 40% of Earth’s land surface used to be grasslands. They’re the right solution in some locations and more appropriate than forests in drier climates, Schneider said.

“Unfortunately, the majority of the world’s grasslands have been converted to pastures and cropland, which has degraded the soil health,” she said. “If you were to heal these grasslands, they would be able to absorb CO2, increasing the organic matter in the soil. An incredibly high percentage of the CO2 in the atmosphere that we want to get rid of could be taken up by the world’s grasslands. And, simultaneously, improving grassland soil health will also make them more resilient to droughts – a win-win.”

Megan King, multimedia editor for the Cornell Lab of Ornithology contributed to the development and production of this story.