Thursday, May 5, 2011

Louisiana vs Northern Waterthrush

The differences between Louisiana and Northern waterthrushes are subtle. On 3 May, we saw both species in the western unit of the Cannon River Wilderness Area in Rice Co. The first two photographs are of the Louisiana Waterthrush we saw; the second two are of Northern Waterthrushes, banded near Dundas in 2008 (third photo) and on 4 May 2011 (last photo).
So how do you tell these birds apart?

1) Throat.  In these photographs, you can clearly see that the throat of the Louisiana Waterthrush is plain white, unlike the finely speckled throat of the Northern Waterthrush.  This field mark is usually good, except these speckles can vary in both species.

2) Eyestripe.  The Louisiana Waterthrush's eyestripe is white and broad (specially behind the eye).  The Northern Waterthrush's eyestripe tapers to a point behind the eye and is often dusky.

3) Flanks.  The flanks of a Louisiana Waterthrush are often buffy, contrasting with the white breast.  This color may be subtle, as you can see in the photo above.

4) Leg color.  Note the bright pink legs on the spring Louisiana Waterthrush in the photos above.  The Northern Waterthrush tends to have dusky, horn-colored legs.

4) Size.  Most Louisiana Waterthrushes are at least a quarter of an inch larger than Northerns.  Good luck discerning this size difference in the field.
Just to make this situation a bit trickier, Northern Waterthrushes vary in underpart color.  Some are white, as is the bird above.  Others are yellowish, like the bird below. Louisiana Waterthrushes are always white-breasted behind the streaks. Yellowish Northern Waterthrushes have yellowish eyestripes quite unlike the white eyestripes of all Louisiana Waterthrushes. The eyestripe of a pale Northern Waterthrush, however, can be similar to the color in the Louisiana.

The songs of the two waterthrushes are perhaps the best way to tell them apart.  This field mark only works if the birds are singing!  In Rice Co., Louisiana Waterthrushes breed near limestone cliffs along the Cannon River. Northern Waterthrushes are migrants that breed further north and usually are not singing.  The Northern Waterthrush song ends in a diagnostic "chew-chew-chew." The Louisiana song begins with three clear slurred whistles, followed by a number of twittering notes dropping in pitch (Peterson 1947).  Thayer Birding Software graciously allowed me to use their copy-righted mp3 files of bird calls so that you can listen to the songs of the Louisiana Waterthrush and the Northern WaterthrushThayer Birding Software produces the DVD Birds of North America (Mac and PC versions available), which is well worth the price. This disk contains multiple bird photographs, videos, and bird calls of North American birds.

2 comments:

  1. Thanks for the tutorial, Dan. I need to see a Lousiana this year for my life list, so it's good to be reminded of the subtle ID contrasts!

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  2. We saw a Northern at River Bend yesterday. Life bird for Henry and me.

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