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New advances in the field identification of dowitchers - continued

Cin-Ty Lee and Andrew Birch

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4. Plumage field marks

4.1 Pattern of tail feathers

Tail feather pattern is one plumage feature that is believed not to change significantly with age. It is often cited as a very reliable field mark (Wilds, 1990; Jaramillo et al., 1991; Jaramillo and Henshaw, 1995): on Short-billed, the white (or buff in alternate plumage) bars on the tail feathers are reported to be as wide or slightly wider than the black bars (Fig. 8) whereas on Long-billed, the black bars are wider than the white (or buff in alternate plumage) bars, sometimes even twice as wide (Fig. 3). Paulson (1993), however, has noted that there is considerable overlap in tail feather pattern between Long-billeds and Pacific coast Short-billeds (L. g. caurinus). We have also observed significant variability in tail feather patterns in Long-billeds and Short-billeds along the Gulf Coast (L. g. hendersoni in Texas). Our observations force us to conclude that although Short-billed tends to have wider pale bars on the tail feathers, there are enough exceptions to this "rule" that this field mark should never be used without the context of other field marks. Exceptions to this so-called "textbook" rule can be seen in Figure 19. These cautionary caveats are in agreement with Jaramillo et al. (1991).

4.2 Field marks in juvenal plumage

Dowitchers are easiest to separate in juvenal plumage. Tertial pattern is an easy and reliable field mark. Fresh juvenal tertials on Short-billed are overall dark gray, but are fringed with constrasting buff/orange edges and are internally marked by strong buff/orange stripes (Fig. 8) the latter giving a "tiger-striped" appearance (cf. Paulson, 1993). In contrast, Long-billed tertials are dark gray with narrower buff edges and duller internal markings (Fig. 9). It is often erroneously stated that juvenal Long-billed tertials lack internal markings altogether; the example in Figure 9 shows that this is not the case.

Juvenal greater coverts on Short-billed are also strongly patterned whereas those on Long-billed are typically uniform gray. Both species have patterned juvenal scapulars, but those on Short-billed tend to be more strongly marked owing to brighter and bolder buff fringes to the scapulars. Finally, the crown on juvenile Short-billeds has an overall dark brown coloration, which is a manifestation of its chestnut ground coloration upon which are superimposed fine black streaks. The dark brown crown contrasts with the white supercilium. On juvenal-plumaged Long-bills, the crown is slightly grayer, showing slightly less contrast with the rest of the plumage.

4.3 Field marks in basic plumage

Basic plumaged dowitchers present the greatest identification challenges. There are, however, some field marks that, when collectively used, are fairly reliable. The sides and flanks on Long-billed tend to be washed with dusky to dark gray vertical bars (Fig. 13, Fig 20, Fig 21). On Short-billed, the flanks and sides have slightly paler gray splotches or spots; these spots are occasionally arranged in a somewhat vertical barred pattern, but overall, the spotting is sparser than the barring on Long-billed (Fig. 4, Fig 12, Fig 18, Fig 19). Thus, the sides and flanks of Short-billed tend to be slightly paler overall and as consequence the contrast between the sides/flanks and white belly is less than that seen in Long-billed.

Chest coloration is also a helpful field mark. On Long-billed, the chest appears to be composed of a continuous and uniform dark wash. On Short-billed the gray color of the chest is composed of small spots or streaks upon close inspection. As a consequence, Long-billed has a slightly darker chest that contrasts more with the white belly than Short-billed. We also note that the slightly darker chest of Long-billed is more sharply demarcated from the white undersides, whereas that on Short-billed is only slightly demarcated.

Another helpful field mark is that the dark wash on the chest of Long-billed grades gradually into the chin (Fig. 22). However, on Short-billed, the entire chin tends to be whiter or paler (Fig. 22). From a distance, this often gives Short-billed a pale-chinned appearance whereas Long-billed often has a more uniform gray wash from the chin down to the upper chest or a limited region of paleness confined to the chin. The Short-billed’s slightly pale chin gives this species a somewhat "belted" appearance, which is not as pronounced as in Long-billed. The more extensive pale chin on Short-billed can be seen on sleeping birds (Fig. 16). Sleeping Long-billeds show less obvious pale chins (Fig. 21).

4.4 Field marks in alternate plumage

The identification of alternate plumaged dowitchers is often much more difficult than standard field guides or texts portray. Jaramillo et al. (1991) recognized this challenge and presented a detailed study of the field identification of alternate plumaged birds. In this section, we focus primarily on field separation of Long-billed and Short-billed Dowitchers. Subspecific variation in Short-billed is presented in the following section.

The most commonly cited field mark in alternate plumage is the difference in underpart coloration and in the pattern of barring or spotting on the flanks and sides of the breast. On all three subspecies of Short-billed, the sides of the breast are typically spotted whereas the sides of the breast on Long-billed are barred (flanks of griseus and caurinus Short-billeds may be slightly barred). In fresh alternate plumage, these features are generally reliable, provided one can get close-enough views to see these features. Another characteristic that has been reported in the literature is that Short-billeds tend to have paler bellies whereas the entire underparts of Long-billed are typically orangish red. The problem is that in worn alternate plumage (almost all southward bound migrants are in worn alternate), the barring and/or spots can be non-existent due to fading and wear. In addition, birds in transition to or from alternate plumage can be characterized by highly variable underpart coloration. Transitional birds of both species may have unusually pale bellies associated with basic plumage, rendering the above-mentioned field marks somewhat ambiguous. Below, we present a few under-appreciated field marks that, when used in combination with underpart coloration and pattern, will greatly aid in field identification.

Lower scapulars and greater and median coverts — Although not explicitly presented in the literature, we found that all subspecies of Short-billed have lower scapular and median and greater covert patterns that differ distinctly from that of Long-billed (Fig. 23). The diagnostic feature is the shape and extent of the feather tips. The alternate-plumaged lower scapulars and median and greater covert feather tips on both species are edged with white. On Short-billed, the white edges on the feather tips continue up the feather, gradually grading into buff feather edges. This gives the lower scapulars and covert feathers on Short-billed a distinct V-shaped appearance. On Long-billed, the white on the edges of the lower scapular and covert feathers is largely confined to the tips. The upper part of the white edges of the feather tips stop abruptly and is often separated from the buff edges of the upper parts of each feather by a black bar across the feather. Thus, the white feather tips on Long-billed do not typically show a V-shape but instead appear to have flat tops and only shallow indentations. Although one might think these features can only be seen with careful close-up scrutiny, these overall differences can actually be seen from afar. On Long-billed, the "squared off" tops of the white feather tips often gives fresh alternate Long-billeds a white-barred appearance from a distance. On Short-billed, the V-shaped covert feather tips and more extensive buffy edges to the lower scapular and covert feathers tend to give a more striped appearance to the upperparts (cf. Jaramillo et al., 1991). This results in an overall lighter coloration to the upperparts on Short-billeds than on Long-billeds.

One advantage of the lower scapular and covert feather field mark is that even in highly worn alternate plumage (July or August), a few relatively unworn lower scapular and covert feathers usually remain (Fig 1 and Fig 24). These unworn feather tips often stand out in worn alternate plumage because the rest of the upperparts appear darker due to the abrasion of the pale feather edges. However, even in the case in which all alternate plumaged feathers exhibit wear, the foregoing field marks can still be used. After the pale feather tips have been worn down, the shape of the alternate lower scapular and covert feathers tend to retain the shape of the dark feather centers. Thus, in Short-billed, wearing away of the V-shaped white feather tips results in deeply pointed black scapular and covert feathers (Fig. 24). In Long-billed, worn lower scapular and covert feathers accordingly have a more squarish or blunt tip (Fig. 1). It is also important to highlight that although most the whitish tips of the lower scapular and covert feathers in worn alternate plumaged birds are often worn away, the upper edges of these feathers are usually less worn. Because Short-billed shows more extensive white edging than on Long-billed, this feature is often still preserved in worn alternate plumage, such that late summer Long-billeds appear very dark-backed while Short-billeds appear lighter-backed from a distance.

Underparts and sides of breast — In fresh full alternate plumage, Long-billeds are characterized by extensive dark reddish underparts and sides of breasted marked by vertical black bars edged with white fringes (Fig. 3). The pattern of barring is only visible in close-up views. However, when this feature is seen, it is diagnostic of Long-billed and has been widely reported or illustrated in the literature. It is important to note that the black bars and their white fringes are very delicate such that they are often worn away by the end of May (cf. Jaramillo et al., 1991). In worn alternate plumage, Long-billeds often have clear sides and appear dark reddish throughout the undersides (Fig. 1).

Short-billeds in fresh alternate plumage (Fig. 11) are characterized by orangish underparts that are slightly lighter than that of Long-billeds. Short-billeds also tend to have more white on the belly or vent, ranging from small amounts of white on the vent of L. g. hendersoni to an extensively pale belly in L. g. caurinus. Instead of the white-fringed black bars of Long-billed, the side of the breast on Short-billeds is characterized by round black spots. The extent of spotting on the sides of the breast in Short-billed is highly variable. The spots are many in L. g. caurinus but sparse to non-existent in L. g. hendersoni. These side spots appear to be more easily retained than the black bars on Long-billed. As such, on worn alternate Short-billeds, the sides remain somewhat spotted unlike Long-billed (Fig. 1, Fig 2).

5. Voice

The best field mark for distinguishing the two dowitcher species is voice. Short-billed gives a "call tututu, a staccato series of low, musical notes a bit faster than but similar to those of a Lesser Yellowlegs" (Paulson, 1993). Long-billed typically gives a higher pitched keek or peep call often repeated several to numerous times in rapid succession. The difference in voice is regarded as a nearly fail-proof field mark, and over the course of our studies.

6. On the identification of Short-billed subspecies

The three subspecies of Short-billed Dowitcher show subtle differences in alternate plumage, but are indistinguishable in basic and juvenal plumages. In general, in fresh alternate plumage hendersoni has the most extensive reddish coloration. On hendersoni, the upper chest, breast, and belly are reddish, leaving only the flanks and undertail coverts whitish. The eastern subspecies griseus appears to have the least amount of red/orange on its underparts in fresh alternate plumage. In griseus, the upper chest, face and chin will have a orangish wash, but the breast, belly, flanks and undertail coverts are typically whitish. The western subspecies caurinus appears to be intermediate between hendersoni and griseus in terms of the extent of reddish/orangish coloration on the undersides.

Other differences include the pattern of the barring/spotting on the flanks in fresh alternate plumage. On hendersoni, the sides and flanks are marked by sparsely spaced spots or small chevrons. In some cases, the spotting on the sides of hendersoni are so sparse that the sides look uniformly red/orange until closer inspection. On caurinus and griseus, the sides are more extensively marked and often are arranged in the appearance of bars or chevrons rather than spots (Fig. 25).

The pattern of lower scapular and covert feathers also differs subtly among the subspecies. In hendersoni and caurinus the upper edges of these feathers are fringed buff or orange whereas in griseus the upper edges are fringed white. The width of the pale fringes to the lower scapular and covert feathers tends to be thicker on hendersoni than on caurinus and griseus. Overall, hendersoni will thus appear to have much brighter and buffier upperparts when viewed from a distance. In contrast, griseus and caurinus have overall darker upperparts (due to the thinner pale fringes), with griseus appearing white-striped and caurinus appearing orange-striped.

Despite these subtle differences, we leave the reader with two caveats. First, these differences pertain only to fresh alternate plumage. When birds are in transition or in worn alternate plumage, the amount of reddish coloration on underparts can be highly variable. In addition, scapular and covert feather coloration and patterns and the extent and pattern of markings on the sides and flanks will also vary with wear and molt stage. Thus, subspecific identification is, at best, only possible within a narrow window of time (spring). The second caveat is that that there is considerable overlap in these plumage features. In fact, Pitelka (1950) emphasized that structural and plumage differences between the three subspecies exhibit clinal gradation from western to eastern populations. Birds with intermediate characteristics are best left unidentified at the subspecies level. Any claim that all alternate-plumaged Short-billeds can be identified to the subspecific level should be met with skepticism.

7. Habitat

7.1 Winter and migration

These two species, in general, prefer different habitats on their wintering grounds. Short-billeds prefer saltwater habitats, thus are usually found feeding on estuarine mudflats and open ocean shores/beaches. However, by no means is this habitat preference strict. For example, wintering Short-billeds can often be found in shallow freshwater pools along the immediate coast in Texas. We note, however, that where wintering Short-billeds have been found in freshwater, saltwater environments are usually in very close proximity. We speculate that although Short-billeds along the coast prefer saltwater habitats, they can often be forced to feed or roost in nearby freshwater environments during high tides.

In contrast to Short-billeds, the habitat preference of wintering Long-billeds may be stricter. Long-billeds prefer freshwater habitats, such as marshes, the edges of freshwater lakes, concrete-lined river channels, etc. They may occasionally frequent saltwater environments along the coast, but in these cases, they tend to the upper reaches of estuaries, where there is more vegetation and the water is less saline. Long-billeds are very rarely seen feeding out in estuarine mudflats or ocean beaches. Figure 1 shows an example of a Long-billed and Short-billed Dowticher feeding side-by-side in saline water at Bolivar Flats in Texas during July.

Despite these general habitat preferences on wintering grounds, we caution birders not to rely too heavily on this field "mark", particularly during migration. During migration, shorebirds can be found in almost any type of aquatic habitat, especially when the choices are limited. This is certainly the case for birds migrating through the continental interior. However, even along the upper Texas coast, we regularly observe, during migration, a few Short-billeds in flooded rice fields within large flocks of Long-billeds. Similarly, at the Salton Sea in southern California, both species are found along the shores of this inland saline lake (pers. obs.).

7.2 Breeding grounds

The habitats on the breeding grounds of both species also differ although both species breed in freshwater habitats (cf. Bent, 1927). The difference is that Long-billed breeds in open arctic tundra in western and northern Alaska, whereas Short-billed breeds in bogs in the boreal forests of southern Alaska and Yukon, central Canada, and the Maritime Provinces (Bent, 1927; Pitelka, 1950). The nesting habitat for Long-billed tends to be more open, being composed of low-lying groundcover characteristic of the northern tundra. In contrast, the nesting grounds for Short-billed are interspersed with bushes and trees.

8. Are structural differences related to differences in habitat preference on breeding grounds

As discussed earlier, the more obtuse loral angle on Short-billed is a manifestation of the higher placement of the eye on the head compared to Long-billed. Can this structural difference be related to differences in habitat preference on breeding grounds According to Pitelka (1950), Short-billeds do not range further north than the northern limit of the boreal forest or taiga. The forested bogs, where Short-billeds nest, are characterized by much denser vegetation than the arctic tundra breeding grounds of Long-billeds. In the former, the presence of shrubs and trees may give rise to statistically more obstructed views. Could the higher placement of the eyes on Short-billed be an evolutionary feature that allows nesting birds to scan more of the sky in a habitat with obstructed views It is often speculated that the higher placement of the eye on snipes and woodcocks is also an evolutionary response to the preferred habitats of these birds — forested bogs and weedy fields. The distinct structural difference in the placement of the eye combined with other structural differences outlined by Pitelka (1950) suggests that the two dowitcher species are not as genetically related as their superficial plumage characteristics might suggest. Avise and Zink (1988) showed using mitochondrial DNA that, despite their superficial similarities, Short-billed and Long-billed Dowitchers are more genetically divergent than certain species of Dendroica warblers and Aythya ducks.

Acknowledgments

We thank Carla Cicero for access to specimens at the University of California at Berkeley Museum of Vertebrate Zoology and Kimball Garrett for access to the Los Angeles County Natural History Museum. The first author is indebted to the late Ned K. Johnson (UC Berkeley Museum of Vertebrate Zoology) and the late Raymond Paynter (Harvard University) for inspiration and encouragement. We thank Brian J. Small, Martin Birch, Ron Weeks and Brush Freeman for discussions. Matthew Hysell, Jo-Szu Tsai, Tokio Sugiyama, Akira Yamamoto, and Kinjo Yonemoto are thanked for photographs or acquiring them.

References

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