Saving the Cerulean Warbler in the Capital Region

Management of the Kittatinny Ridge Conservation Landscape has meant optimizing particular patches of land in order to benefit specific species. An effective example of this strategy are efforts surrounding the cerulean warbler.

The cerulean warbler is a songbird that breeds throughout Eastern North America in mature hardwood forests, specifically preferring to nest and forage in the high canopy of older trees, especially oak[1]. Each year, the cerulean warbler migrates as far as the Andes Mountains in South American to winter. Yet habitat loss in both the cerulean warbler’s breeding and non-breeding range has caused it to be one of the fastest declining tropical migrant bird species in the U.S., with a 70% population loss since 1970. In Pennsylvania, extensive clearcutting has all but all eliminated the old, structurally complex forests these birds rely on[2]. Saving the cerulean warbler requires conservation efforts both in their winter homes in South America as well as their habitat in Eastern North America, and the Kittatinny Ridge is home to prime habitat for both migrating and breeding cerulean warblers.

Habitat connectivity is also particularly important for this species. Even where there is prime habitat available for the warbler, that habitat will likely remain empty of ceruleans if there isn’t an established population nearby. For this reason, as conservationists aim to manage forests in ways that support cerulean warblers, it’s important to site these projects near existing populations[3].

Expanding habitat for the cerulean

Two such projects are being carried out in the Harrisburg area by The Nature Conservancy and Audubon Mid-Atlantic. These organizations are helping to manage land owned by the Capital Region Water Authority to support cerulean warblers and expand preserved warbler habitat at nearby Cove Mountain.

In 2017, The Nature Conservancy purchased roughly 350 acres of Hamer Woodlands at Cove Mountain. Located in Marysville, Pennsylvania (a mere 8 miles from the state Capitol building in Harrisburg), habitat like that found at Hamer Woodlands is increasingly rare in the capitol metropolitan region, as more and more open spaces have been lost to encroaching development.

Hamer Woodlands location in the capital region.Photo by The Nature Conservancy | Used by permission

The conservation goal for the Hamer Woodlands was not only to protect the land itself, but to manage it in a way that would optimize it as both a stopover and summer nesting habitat for migrant bird species like the cerulean warbler[4]. In 2021, The Nature Conservancy expanded the Hamer Woodlands with the purchase of an additional 1,200 acres, quadrupling the preserve size and connecting it to adjoining conserved lands, creating a 14 mile stretch of protected land along the Kittatinny Ridge. This acquisition increased both local terrestrial connectivity and expanded the area as a stepping stone for migrant bird species passing through[5].

A bit farther north, across a bend in the Susquehanna River at a Capital Region Water Authority property near Halifax, Pennsylvania, there are similar efforts to optimize woodland for cerulean warblers underway. 100 new acres of habitat have been created by managing a mixed-species forest stand to encourage the growth of large white oak, which are a key part of cerulean warbler habitat and which had been previously struggling on the property. Also important is the lot’s proximity to nearby Peter’s Mountain, where there is an established cerulean warbler population to colonize the new habitat[6].

The dual purposes of supporting migrant songbirds on their journey and encouraging cerulean warblers to stop and nest required altering the forest in different ways. To ensure migrant songbirds have enough to eat on their stopovers, invasive species were removed and an understory of native fruiting shrubs were planted[7]. To meet the very specific nesting requirements of the cerulean warbler, which nests high in the top of the canopy near open gaps between the branches, the land was managed in a way that focused on improving the health of the white oak trees that ceruleans favor for their nests[8]. Oak trees also host a particularly high number of insects that the insectivorous cerulean warbler eats.

This management included removing other tree species that were competing with the white oak and creating the canopy gaps the cerulean looks for. The selective removal of these other trees is called a shelterwood harvest. Beyond the immediate benefit for that season’s nesting warblers, this thinning of the canopy allows more light to reach the forest floor, encouraging the growth of the white oak, which isn’t particularly shade tolerant, thus ensuring the next generation of oaks are available to support cerulean warblers well into the future[9].

A mature oak forest after a shelterwood cut – note the spaces in the canopy and light that reaches the forest floor.Photo by Indiana Department of Natural Resources | Public Domain

In large part due to habitat conservation efforts like
this, populations of the cerulean warbler have stabilized in many parts of the Appalachian Mountains. Given this, the North American Bird Conservation Initiative’s 2022 State of the Birds report highlighted the cerulean warbler as a success story[10].

References

1. Sean Grace, Does the Cerulean Warbler Have the Blues (blog post), 6 July 2021.

2. Appalachian Mountains Joint Ventures, Cerulean Warbler: Management Guidelines for Enhancing Breeding Habitat in Appalachian Hardwood Forests. February 2013.

3. Ibid.

4. Scott Parkhill, Audubon Mid-Atlantic, Partnership-based Conservation at Cove Mountain & Kittatinny Ridge (blog post), 26 April 2024.

5. Kittatinny Ridge Conservation Landscape, PA DCNR, A Sustainable Model for Landscape Protection (blog post) 26 August 2024.

6. Scott Parkhill, Forest Program Manager, Audubon Mid-Atlantic, personal communication, 9 December 2024.

7. Kittatinny Ridge Conservation Landscape, PA DCNR, A Sustainable Model for Landscape Protection (blog post), 26 August 2024.

8. Appalachian Mountains Joint Ventures, Cerulean
Warbler: Management Guidelines for Enhancing Breeding Habitat in Appalachian Hardwood Forests. February 2013.

9. Appalachian Mountains Joint Venture, Virtual Training:
Forest Management for Birds, accessed 19 February 2025.

10. U.S. North American Bird Conservation Initiative,
State of the Birds Report: United States of America, 2022.