Battling to Save Battlefield Birds

By Nicholas Tait, NCRN I&M Science Communication Intern

Grassland birds are among the fastest declining bird species in the United States.

Cornell Lab of Ornithology

Grassland Birds in Peril

Grassland birds are in steep decline across the United States, particularly in the country's east. In the past 50 years, more than 700 million breeding grassland birds, representing 31 species, disappeared and declines have been reported in 74% of North American grassland bird species—higher than any other bird group in the US. The loss of grassland habitats to development, forest, and intensive agriculture is a major driver of these downward trends.

Contemporary farming practices favor fields of corn and soybeans (row crops) over pasture and hayfields which are better suited to the needs of grassland birds. Hay and pasture have an abundance of the grass and twigs the birds use to make their nests, while row crops lack suitable habitat to reproduce. In the agricultural areas that do become hayfields, earlier and more frequent harvests leave birds without habitat for reproduction, destroy nests, and kill the baby birds inside nests before they can survive on their own.

The loss of grassland bird species has a profound impact on parks and their ecosystems. Grassland birds are an indicator species of a healthy ecosystem and serve valuable ecological functions in these habitats (e.g., preying on insects, becoming food for predators, dispersing seeds). Additionally, many visitors to the parks hope to hear the fluted song of the eastern meadowlark and the insect-like hum of the grasshopper sparrow when traversing trails through grassland habitat. Preserving the future of grassland birds is a must in pursuit of the NPS mission to maintain natural and historic areas for generations to come.

Battlefields as Refuges

Due to the rapid population declines, scientists and resource managers have made considerable efforts to learn about the habitat needs of grassland birds and how agriculture and other land management practices impact them.

In national parks of the National Capital Region, habitats suitable for declining grassland species mainly occur at the Civil War battlefield parks of: Antietam National Battlefield (ANTI), Harpers Ferry National Historical Park (HAFE), Manassas National Battlefield Park (MANA), and Monocacy National Battlefield (MONO). These parks preserve grasslands and agricultural areas as part of the Civil War-era landscape, even as surrounding areas urbanize and change. As a result, battlefield parks represent permanent habitat for grassland birds in an otherwise rapidly developing region.

To better understand populations in the parks, the NPS has monitored grassland birds every year at MANA since 2014, at ANTI since 2015, and at MONO and HAFE since 2016.

A recent analysis of this monitoring data aimed to uncover how battlefield parks and their land management —farming practices in particular—help conserve grassland birds. The authors analyzed data collected through 2021 on eastern meadowlarks (Sturnella magna) and grasshopper sparrows (Ammodramus savannarum) at the four battlefield parks. These two contrasting species represent a wide spectrum of grassland bird habitat needs.

Researchers first looked at how bird occupancy (whether a species is present or absent at a given location) varied across the different parks over time. They found that each had different occupancy levels of grasshopper sparrow and meadowlark (Figure 1). MANA had the highest occupancy for both species, and MONO had the lowest—Eastern meadowlark was seldom detected at MONO.

Figure 1: Observed breeding-season occupancy, by park, of 2 focal bird species monitored in National Capital Region battlefield parks.
Figure 2: Predicted breeding-season occupancy by field type. WSG = native warm-season grass; CSG = non-native cool-season grass.
Figure 3: Predicted breeding-season occupancy in delayed hay harvest areas and years since delayed harvest began. Year 0 indicates first year in which harvest was delayed. Error bars and shaded areas indicate 95% confidence intervals.

NPS

Agricultural Leasing for Pasture and Hay Plus Late Mowing Helps Birds

Researchers looked at land cover and agricultural practices in the surrounding landscape to figure out why species occupy each park at different levels.

One approach beneficial to grassland birds is the use of agricultural leases. Agricultural lease programs maintain a park’s agricultural working lands and can support grassland birds as well. Leasing programs permit farmers to use fields for crops or grazing, which helps parks maintain a historic landscape appearance and keeps the area from becoming forested, thus maintaining open habitat that could be used by grassland birds. The recent analysis of grassland bird data showed that eastern meadowlark and grasshopper sparrow occupancy varies across a spectrum of habitat types within the parks (Figure 2). Unleased areas (mainly derelict fields and road edges) and row crops had the lowest occupancy levels, whereas hayfields and pastures hosted more meadowlarks and grasshopper sparrows.

Another management action that protects grassland birds is to delay the year’s first hay harvest (also called mowing) until mid-July or later. This timing increased occupancy for both eastern meadowlark and grasshopper sparrow, likely allowing the birds to successfully raise young in cultivated fields. The benefits of these harvest delays can also accumulate over time. Grasshopper sparrows and meadowlarks were more likely to occupy fields with multiple, consecutive years of delayed harvests than fields where harvest delays had just begun or had not yet been implemented. Including mowing guidelines in agricultural lease agreements and park management plans can drastically increase the survival and occupancy of grassland birds (Figure 3).

Open Fields and Prescribed Fire Help Too

Other types of vegetation management in grasslands can also improve habitat for birds. Many grassland bird species are area-sensitive and typically do not use fields below a certain size and avoid forested field edges. These birds are adapted to expansive grassland habitats where aerial threats such as raptors can be easily spotted, and their nests are safer from raccoons, foxes, or other forest-dwelling predators.

To reduce this type of “visual enclosure” and preserve ideal habitat for grassland birds, park managers can control encroaching forest edges and remove shrub islands and tall trees along fence lines that visually divide fields.

Prescribed fire is another tool that parks can use to manage vegetation and help grassland birds. Burning reduces woody shrub cover, removes dead thatch from the ground, and encourages regrowth of native plants. The research showed that grasshopper sparrows were more likely to occupy areas that had been burned within the past two years. Eastern meadowlarks showed no change.

Grassland Birds in NCR Parks

The National Park Service is working hard to preserve grassland birds. All four battlefield parks in our region have grassland restoration projects either in progress or forthcoming. Additionally, NCRN I&M will continue long-term monitoring to provide park managers with updated data on the status of grassland bird populations in our region.

To see all the grassland species encountered during NCRN monitoring, check table below.

Common name	Scientific name	Antietam	Harpers Ferry	Manassas	Monocacy
Northern bobwhite	Colinus virginianus	-	-	1.4%	-
Mourning dove	Zenaida macroura	32.9%	11.8%	9.9%	13.5%
Killdeer	Charadrius vociferus	0.8%	0.3%	0.7%	2.6%
Northern harrier	Circus hudsonius	-	-	-	0.1%
American kestrel	Falco sparverius	0.8%	0.3%	0.9%	0.4%
Eastern kingbird	Tyrannus tyrannus	18.5%	9%	6.6%	6.8%
American crow	Corvus brachyrhynchos	17.2%	21.6%	16.2%	6.4%
Common raven	Corvus corax	0.4%	5%	-	0.4%
Horned lark	Eremophila alpestris	3.4%	0.3%	-	8.9%
Barn swallow	Hirundo rustica	12.4%	4.5%	11.2%	12.7%
Grasshopper sparrow	Ammodramus savannarum	48.7%	49.9%	55.2%	23.7%
Field sparrow	Spizella pusilla	68.2%	55.4%	48.4%	11.8%
Vesper sparrow	Pooecetes gramineus	1.1%	0.3%	0.7%	0.2%
Savannah sparrow	Passerculus sandwichensis	0.1%	-	0.5%	0.3%
Bobolink	Dolichonyx oryzivorus	0.3%	-	0.1%	0.7%
Eastern meadowlark	Sturnella magna	18%	29.8%	57.3%	1.4%
Red-winged blackbird	Agelaius phoeniceus	4.8%	49.9%	30%	16.3%
Brown-headed cowbird	Molothrus ater	25.8%	16.5%	8.3%	24.1%
Common grackle	Quiscalus quiscula	4.4%	5.8%	3.8%	10.3%
Dickcissel	Spiza americana	-	-	0.2%	-

Table 1: Grassland-dependent/reliant species detected during NCRN I&M grassland bird point count surveys in National Capital Region battlefield parks (2014-2021). Percent of surveys on which the species was detected are indicated for each park.
NPS

This article is based on findings in: Massa, Megan, Elizabeth Matthews, W. Gregory Shriver, and Emily Cohen. “Response of Grassland Birds to Management in National Battlefield Parks.” The Journal of Wildlife Management, October 18, 2023. https://doi.org/10.1002/jwmg.22519

Further Reading

Read how grassland restoration efforts at Manassas National Battlefield Park has helped pollinators: Prospering Pollinators in Manassas Grasslands (U.S. National Park Service) (nps.gov)