Yellowlegs and Northern Thrush
by Dr. Robert "Bob" White
Dave Kandz, the Conservation Chairman and 2nd Vice-president of St. Petersburg Audubon passed along the photo below of two Greater and one Lesser Yellowlegs. They were foraging together in the now wet field at 102nd Ave and 9th St No in north St. Petersburg. It made me think about how some times it can really be difficult to tell whether you're seeing a Greater or a Lesser Yellowlegs when seeing them at a distance.When looking at Dave's great photo it is easy to see that the two birds on the right are Greaters and the bird on the left is a Lesser. There is a size difference that makes it easy to tell them apart, but when seen alone size is less definitive. The Lesser has a short, straight bill that is no longer than its head. A Greater's bill is longer than its head and is typically slightly upcurved (more noticeable in the bird at right). The Lesser's bill is always black, sometimes with a touch of gray at the base of the upper mandible in juveniles. A Greater's bill is black, with the base of it being extensively gray in non-breeding adults and juveniles. Sometimes this is hard to see with just binoculars at a distance, but can be picked out when viewing from a scope. This time of year most, if not all, the yellowlegs we see will be in non-breeding plumage or are juveniles.
A Greater Yellowlegs has twice the "bulk" of a Lesser and its voice is a loud, ringing three-or-four noted tew tew tew tew or klee klee klee. The Lesser Yellowlegs, meanwhile, has an almost as loud, two-noted tu tu that is considered much less musical or ringing as that of a Greater.
Suzi Fleck photographed a Northern Waterthrush at Sawgrass Lake Park recently and in her excellent head-on photo, below, we can see several of the characteristics that makes this bird a Northern and not a Louisiana. But before we get to that, keep in mind that as we enter the second half of September our chances of seeing a Louisiana become slimmer and slimmer. Though the latest in fall Louisiana for Pinellas is September 28th, they are really just an occasional migrant after the 1st of September, unlike the Northern which is seen into October.
In the photo you can see that the Northern's supercilium, or eyebrown stripe, is of even width throughout and that it is pale yellowish, unlike that of a Louisiana's which is generally described as being whiter and then wider as it progresses behind the eye.
A Northern usually has a spotted throat (as this bird shows) whereas a Louisiana's throat is usually unspotted. The dense blackish brown spots on the underparts align themselves to form neat streaks. In a Louisiana the streaks are sparser, paler and are less neatly arranged into rows. We cannot get a feel for how large (or not) the bill is on Suzi's bird, but a Louisiana has a slightly heavier and larger bill. We can see, however, the leg color. The leg color of a Louisiana Waterthrush is often described as being bubblegum. The legs of a Northern are duller, more dusky pink.
And finally, there is a difference in the way each of the two species bob their tails (obviously not shown in the photo). The Northern has a faster, more up-and-down tail bobbing motion, while the Louisiana's tail bobbing is more circular and involves more body motion.