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Grassland birds in trouble
Grassland birds are declining steeply across the United States, especially in the East. Over the past 50 years, more than 700 million breeding grassland birds of 31 species have disappeared, and 74% of North American grassland species have declined — more than any other U.S. bird group. The main cause is lost habitat, to development, forest and intensive agriculture.
- Crops have changed: farms now favor row crops such as corn and soybeans over pasture and hayfields, which offer the grasses and twigs birds build nests from; row crops offer nowhere to breed.
- Hay is cut earlier and more often, leaving birds without breeding habitat, destroying nests and killing nestlings before they can fend for themselves.
Their loss matters to parks. Grassland birds are an indicator of ecosystem health; they eat insects, feed predators and spread seeds. And many visitors come hoping to hear the fluting song of the eastern meadowlark or the insect-like buzz of the grasshopper sparrow.
Battlefields as refuges
In the National Park Service's National Capital Region, good grassland habitat is found mainly at four Civil War battlefield parks: Antietam, Harpers Ferry, Manassas and Monocacy. They keep grasslands and farmland as part of the Civil War–era landscape — making them permanent habitat in a fast-developing region.
The NPS has surveyed grassland birds yearly at Manassas since 2014, Antietam since 2015, and Monocacy and Harpers Ferry since 2016. A recent analysis of data through 2021 looked at two contrasting species spanning a range of habitat needs: the eastern meadowlark (Sturnella magna) and the grasshopper sparrow (Ammodramus savannarum).
Occupancy — whether a species is present at a spot — differed by park: Manassas had the highest for both species and Monocacy the lowest, where meadowlarks were seldom detected.
Breeding-season occupancy of the two species by park, by field type (native warm-season versus non-native cool-season grass), and by years since hay harvest was delayed. NPS
What helps
1. Leasing land for hay and pasture. Agricultural lease programs let farmers crop or graze park fields, keeping the historic look and stopping fields from turning to forest. Hayfields and pastures held the most meadowlarks and grasshopper sparrows; unleased areas (mostly derelict fields and road edges) and row crops held the fewest.
2. Mowing late. Delaying the year's first hay cut until mid-July or later raised occupancy for both species, probably letting them raise young in the fields. The benefit builds over time: fields with several consecutive years of late mowing were more likely to have both birds than fields where the delay was new or not yet in place. Writing mowing rules into lease agreements and park plans can greatly improve the birds' survival and occupancy.
3. Keeping fields open. Many grassland birds are area-sensitive: they avoid small fields and forest edges, preferring wide spaces where they can spot raptors and where nests are safer from raccoons, foxes and other forest predators. Managers can reduce this "visual enclosure" by holding back encroaching forest and removing shrub islands and tall trees along fence lines.
4. Prescribed fire. Burning cuts woody shrubs, clears dead thatch and encourages native plants. Grasshopper sparrows were more likely in areas burned within the past two years; meadowlarks showed no change.
Birds of the battlefields
All four parks have grassland restoration projects under way or planned, and monitoring will continue. Share of surveys, 2014–2021, on which selected grassland species were detected:
| Species | Antietam | Harpers Ferry | Manassas | Monocacy |
|---|---|---|---|---|
| Grasshopper sparrow | 48.7% | 49.9% | 55.2% | 23.7% |
| Eastern meadowlark | 18% | 29.8% | 57.3% | 1.4% |
| Field sparrow | 68.2% | 55.4% | 48.4% | 11.8% |
| Red-winged blackbird | 4.8% | 49.9% | 30% | 16.3% |
| Mourning dove | 32.9% | 11.8% | 9.9% | 13.5% |
| Brown-headed cowbird | 25.8% | 16.5% | 8.3% | 24.1% |
| Eastern kingbird | 18.5% | 9% | 6.6% | 6.8% |
| Barn swallow | 12.4% | 4.5% | 11.2% | 12.7% |
| Horned lark | 3.4% | 0.3% | — | 8.9% |
| Northern bobwhite | — | — | 1.4% | — |
| Bobolink | 0.3% | — | 0.1% | 0.7% |
| Dickcissel | — | — | 0.2% | — |
Sources
Based on "Battling to Save Battlefield Birds," by Nicholas Tait, NCRN I&M Science Communication Intern, National Park Service, drawing on Massa, Matthews, Shriver and Cohen, "Response of Grassland Birds to Management in National Battlefield Parks," The Journal of Wildlife Management, 2023; rewritten in hubnx's own words. A graphic credited to the Cornell Lab of Ornithology is not reproduced.
Dans ces publicationsAntietam National BattlefieldHarpers Ferry National Historical ParkManassas National Battlefield ParkMonocacy National Battlefield
Licence : CC0 1.0 (domaine public) · Adapté de www.nps.gov
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