(by Pam Hunt)
May is famous for the peak of spring migration in New Hampshire, particularly of warblers, and the third Friday in the month is also “Endangered Species Day.” To honor both of these important items on the calendar, this month’s special additional “Bird of the Month” is a warbler on the NH Threatened and Endangered Species List. The Cerulean Warbler was listed as “threatened” here in 2017 due to declines both locally and nationally. This is a small warbler, so named because of the male’s sky-blue head and back. Because Ceruleans stay high in trees however, this coloration can be hard to see and the view most people get is of the clean white underparts broken by a black breast band.
As befits a threatened species, the Cerulean Warbler is quite rare in the Granite State. It wasn’t even known to occur here regularly until the 1990s, when a small population was discovered in Pawtuckaway State Park. Around the same time there were irregular records from Mount Wantastiquet in Chesterfield and Hinsdale in the southwest corner of the state, and a couple of records from along the Blackwater River in Salisbury. Pawtuckaway was by far the most reliable site, hosting up to at least 4-5 males in some years, but around 2010 the species started to become less reliable there and appears to have disappeared entirely. Over that same time period, reports increased from Wantastiquet, although this may in part be due to more intensive birder visitation. There were at least two males there in 2024.
New Hampshire is at the extreme northeastern corner of the Cerulean Warbler’s range, which is centered on hardwood forests of the Appalachians and Midwest. Across most of this range it has been in decline for over 50 years (Figure 1), leading to extensive study of its habitat and migration. Researchers have found that Ceruleans prefer forests with high canopies and diverse mixes of tree heights in the understory, and in the core range several projects have implemented forestry practices to improve forest structure for the species. This warbler winters in mid-elevation forests of the northern Andes in South America, an area subject to high human pressures such as deforestation for agriculture. To this end, conservation groups have initiated land protection efforts in the non-breeding range, initiatives that also benefit native resident wildlife.
Although rare in New Hampshire, Ceruleans have a stronger toehold in southern New England, where populations are slowly increasing (Figure 1). Most of these birds are in the western portions of Connecticut and Massachusetts and are likely linked by dispersal to the birds in southwestern New Hampshire. In this region they are found mainly in hardwood forests on slopes or ridgelines and with a significant component of oaks. They arrive in early May and can be very hard to find after early July when they stop singing.
Because Ceruleans spend their time high in the forest canopy, they are almost always first detected by their song: a rising series of buzzy notes reminiscent of a Northern Parula or Black-throated Blue Warbler. In fact, many Black-throated Blues in New England have a song variant that is remarkably similar to a Cerulean, and for this reason records of singing Ceruleans in New Hampshire require visual confirmation. Given the species’ rarity and threatened status, we need to be careful that observers are reporting the correct type of warbler.
Are there Ceruleans elsewhere in New Hampshire? It’s certainly possible, and good places to look include other slopeside forests along the Connecticut River and Massachusetts border. Who knows, maybe some lucky observer will find a new site through the combination of good ears, patience, and a strong neck to scan the treetops for a little bit of the sky in warbler form.
State of the Birds at a Glance:
- Habitat: Deciduous forests
- Migration: Long-distance
- Population trend: Declining
- Threats: Habitat Loss and Fragmentation, including in winter range
- Conservation actions: Conserve non-breeding habitat, Manage forests for diverse structure
More information on “The State of New Hampshire’s Birds” is available here. Full species profiles in the format of “Bird of the Month” are now available here.