Due Diligence with Vermont Dowitchers

By Kent McFarland August 31, 2014
Short-billed Dowitcher (Limnodromus griseus)

Short-billed Dowitcher (Limnodromus griseus) / K.P. McFarland

Wouldn’t it be nice if bird names always told how to identify a bird?  Imagine a world where Red-bellied Woodpeckers had flashy red bellies, Ring-necked Ducks had a neck ring that was as visible, Spotted Sandpipers had spots all year round, Winter Wrens were here in the winter, Little Blue Herons were always blue, and you could tell Long-billed Dowitchers and Short-billed Dowitchers apart by their bill lengths?  Such are the woes and challenges of birders.

In October 2013, a small group of dowitchers flew into the Brilyea Access marsh at Dead Creek WMA in Addison and presented a case study for the significant challenges in determining the species of individual birds for even the most experienced and skilled birders.  Rare Species Documentation forms (RSDs) needed to be evaluated by the Vermont Bird Records Committee for each of the species since Long-billeds have been documented in the state only a few times, and Short-billeds are rarely present at so late a date (October-November).

Bill length problems aside, the other problem in identifying dowitchers is that in the fall, the variety is compounded because we have adults and juveniles as well as the potential for two subspecies of Short-billed Dowitchers.

(a) The first problem in telling the two species apart is figuring out what guide books, websites, apps, and articles to use and trust for birds we see in Vermont, where they are seen only during migration.  That is just about as hard as figuring out the birds.  At the very least, use multiple resources. A great review, although technical, can be found here.  Another website summarizes characteristics from a number of sources and shows that the amount of contradictory, published information is astonishingly high.

(b) The second problem is deciding which characteristics of an individual bird to use in determining the species.  Don’t count on there being a single magical feature that if seen well, will solve your ID dilemma.  Yes, there was one bird in that 2013 Brilyea flock that was often described as having a “ridiculously long bill” and was likely Long-billed.  But even that bird needed documentation of more verifying features.

(c) Third, give yourself lots of time.  ID-ing these birds takes lots of patience, and often lots of experience.

(d) Fourth, document both what you can see and hear, and what you are not able to discern.

So, what should you look for as you view these marvelous shorebirds with sewing machine-like foraging motions in shallow wetlands?  The key is seeing (and hearing, if you can) a variety of features … whose combination could lead to a positive ID.

Fall migrant Dowitchers come in all ages, sexes, stages of moult, and body weights.  Determining as many of these as possible can be a crucial starting point for most identifications.  If a bird is viewed for several weeks, as appeared to be the case with some or all of the 2013 Brilyea birds, plumage, weight, and dimensions can change.  This can confuse or, hopefully, aid identification. Ideally, some of the identification criteria here will help point you in the right direction. But keep in mind, there is no shame in calling an individual a “dowitcher sp.,” especially for distant birds or those in poor light.

Structural characteristics; all ages and plumages: Some of the structural characteristics that can be helpful in identification are summarized below. Along with these characteristics, vocalizations and tail feathers are also generally considered to be invariant with respect to age, so they can be helpful regardless of time of year.

Characteristic Short-billed Dowitcher Long-billed Dowitcher
Leg length1 Shorter Longer
Wing/tail shape (posterior) More truncate More elongated and attenuated
Supercilium More arched Straighter
Posture (relaxed feeding) Straighter backed Hunch-backed
Bill1 Shorter, slight downward bend Longer, straight
Tail feathers (often difficult to see) Black and white bars in tail of even width Black bars in tail wider than white bars
Vocalizations A rapid “tu, tu, tu” A high pitched “keek,” but this can be given in series

1Some sources state that only 1 out of 6 birds have a sufficiently longer bill or longer legs to be positively identified by these characters alone – in other words, use multiple features!

After looking at some of the structural characteristics, plumage patterns can also be helpful, however, with molt, feather wear, adults, juveniles, and multiple subspecies, it is important to start with an assessment of the age and plumage of the bird you are observing.

Plumage characteristics; adult breeding: To effectively use plumage characteristics, it is important to know whether it is spring or fall and whether you are looking at a juvenile or an adult. In spring, dowitchers are relatively uncommon in Vermont, but all birds that pass through will be in alternate (or breeding) plumage.Let’s start with a few characteristics that can help distinguish the two species in alternate plumage. In spring, birds have just molted into their alternate plumage, so their plumage is in better condition than in fall when their feathers are showing the signs of wear. Most of the spring characteristics can still work in the fall, but identification becomes trickier with feather wear and molt.

Spring migration
Characteristic Short-billed Dowitcher Long-billed Dowitcher
Sides of breast and flank Spotted Barred
Lower breast and belly White Brownish-red
Wing coverts V-shaped feathers with white tips Squared off feathers with white tips

Plumage characteristics; adult non-breeding:
The two species are very similar in non-breeding (or basic) plumage and separating them is difficult without vocalizations, structural characteristics, or a great look at the tail. Long-billed Dowitchers tend to migrate south later than Short-bills, and they molt some of their flight feathers during migration. Thus, late birds (Oct-Nov) molting wing feathers are likely going to be Long-billed Dowitchers.

Plumage characteristics; juveniles: Juveniles (birds making their first migration south) are generally easily distinguished by the broad, neat, buffy-red edges to their scapulars, tertials, and coverts (for a review of shorebird feathers, click here).

Juveniles (or juvenal plumage)

Characteristic Short-billed Dowitcher Long-billed Dowitcher
Tertials Fringed with contrastingbuff/orange edges; strong internal markings with buff/orange stripes; looks “tiger-striped” Narrower buff edges; internal markings dull or lacking
Coverts and scapulars More strongly marked; brighter and bolder buff fringes with internal patterning Less strongly marked; limited internal patterning

We can’t overemphasize the use of several supporting features to determine the species.  At this writing, an RSD is required by the Vermont Bird Records Committee and eBird for any Long-billed Dowitcher submission, and for out-of-season Short-billed Dowitcher submissions.  The details can be found at:  http://www.vtecostudies.org/vbrc/checklists.html

(f)  If the species is in doubt, submit the bird(s) to eBird as Short-Billed/Long-Billed Dowitcher [use Add Species on the submission page].

Thanks to Ian Worley, Vermont eBird county editor, and Allan Strong, co-chair Vermont Bird Records Committee, for putting this article together.