Editor’s Note: This article was originally published in the Spring 2014 issue of New Hampshire Bird Records, Vol. 33(1). While the banding station dates may have shifted slightly the patterns hold true.
The Northern Waterthrush and the Louisiana Waterthrush are two very similar species of warblers and are the only members in the genus Parkesia. As their names suggest, they are both thrush-like warblers. They occur most commonly in wetland areas and are often seen on or near the ground. They are very similar in appearance and both occur in New Hampshire, however, many aspects of their breeding and migratory behavior in the state are distinct. I am going to attempt to highlight a few differences that are not found in most field guides.
Identification
Most field guides do a good job at highlighting the differences between these two species. However, I want to emphasize the fact that they can be very difficult to identify based on sight alone. Compounding the problem is the secretive nature of these birds that skulk in brushy tangles of low wetland areas. The songs of the two species are distinct and easy to learn; however, silent birds should be treated with extreme caution when you attempt to identify them.
Editor’s Note: Listen to the differences in song below. For the Northern Waterthrush the song is loud and ringing, described as sweet sweet sweet swee wee wee chew chew chew chew. The Louisiana Waterthrush starts with 2-4 clear notes and then is followed by a lovely jumble.
Habitat
On breeding territory in New Hampshire, both species prefer low thickets in wetland areas; however, the Louisiana Waterthrush typically prefers areas with moving water. This can include small swampy streams to medium sized rivers. The Northern Waterthrush prefers stagnant swampy wetlands, sometimes near small streams. These habitats can overlap and I have seen both species nesting on opposite ends of a swamp nearby in Massachusetts. In migration, the habitat they occupy likely overlaps greatly; however, in all cases, the birds will stay low near the ground in dense thickets.
Breeding Distribution in New Hampshire
The Louisiana Waterthrush is a more southern warbler, restricted to the eastern United States, and reaches the northern limits of its breeding range in New Hampshire. It is an uncommon nesting species and is widespread but local across southern New Hampshire. It is found almost exclusively south of the White Mountains and any sightings north of the White Mountains should be carefully scrutinized and documented, since they are almost certainly a Northern Waterthrush.
The Northern Waterthrush is the widespread northern counterpart to the Louisiana Waterthrush. It nests across most of Canada west to and including almost all of Alaska. In New Hampshire, it is fairly common in northern parts of the state; however, it becomes less common as a nesting species in southern and eastern parts of the state.
Migration Behavior
Perhaps one of the most often overlooked differences between the two species, and the reason behind this article, is the uniqueness of their migration behaviors. The Northern Waterthrush is very similar to the other species of northern warblers in its timing during migration. It arrives here slightly earlier than most, with the first migrants appearing during the last week of April. Peak migration occurs in mid-May when it can be fairly common anywhere in the state. In the fall, the Northern Waterthrush is likely fairly common in migration, although it often goes undetected due to its retiring habits. Reports of more than three or four from a location are rare; however, records from the Appledore Island Migration Banding Station at the Isles of Shoals in Maine show this species to be one of the more commonly captured species from mid-August to mid September (S. Morris, personal communication).
The Louisiana Waterthrush is an early migrating warbler in the state in the spring. They arrive on their breeding grounds about a week earlier than the Northern Waterthrush, with the first birds appearing during the third, or sometimes second, week of April. They are well established on their breeding territories by the beginning of May. In the fall, they are one of the first warblers to completely leave the state. Late nesters may linger into August; however, most, if not all, are gone by mid to late August. Jon Dunn, in National Geographic’s Field Guide to the Birds of Eastern North American, goes further:
“In fall, any waterthrush seen [anywhere in the eastern United States] after about 20 August is almost certainly a Northern, especially on into September.”
The status of “in-transit” migrants (birds that stop over during migration) is still a bit of a mystery. It appears that most Louisiana Waterthrushes fly straight to their breeding grounds when they arrive in New Hampshire and most depart straight to their wintering grounds.
Because we are on the northern edge of their breeding range, there are comparatively few migrants that could possibly pass through our state. This makes them an extremely rare bird of passage, and therefore, extremely rare away from breeding areas.
Bird banding data would seem to support this. The Appledore Island Migration Banding Station has been capturing and banding birds during spring and fall migration for over 30 years (S. Morris, personal communication). Data collected from 1981 through 2013 shows that a total of 7,119 Northern Waterthrushes were captured and banded in their nets as compared to only two Louisiana Waterthrushes!
In addition, during research work on Star Island (Isles of Shoals, New Hampshire) in 2009-2010, a total of 18 Northern Waterthrushes were banded during spring migration and 166 were banded during fall migration, but there were no Louisiana Waterthrushes banded (R. Suomala, personal communication). On a personal level, with 33 years of experience, I have never seen a Louisiana Waterthrush in migration along the immediate coastline or away from known or suspected breeding areas.
The above information can be summarized with three important “rules of thumb” to keep in mind:
1. Any waterthrush sighting in, or north, of the White Mountains is almost certainly a Northern Waterthrush.
2. After August 31, any waterthrush in the state of New Hampshire is almost certainly a Northern Waterthrush.
3. Any waterthrush, at any date, along the immediate coastline, at the Isles of Shoals, or away from breeding grounds of the Louisiana Waterthrush, is almost certainly a Northern Waterthrush.
References
Bird Banding Laboratory Data online. USGS. Patuxent Wildlife Research Center. https://www.pwrc.usgs.gov/ BBL/index.cfm.Accessed October 2014.
National Geographic. 2008. Field Guide to the Birds of Eastern North America. National Geographic Society, Washington, D.C.
Foss, C. ed. 1994. Atlas of Breeding Birds in New Hampshire. Audubon Society of New Hampshire, Concord, NH.
Keith, A. and R. Fox. 2013. The Birds of New Hampshire. The Nuttall Ornithological Club, Cambridge, MA.
Sibley, D. 2014. The Sibley Guide to Birds. Alfred A. Knopf, New York, NY.
Veit, R. and W. Petersen. 1993. Birds of Massachusetts. Massachusetts Audubon Society, Lincoln, MA.