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This article is in 3 parts: Least Peeps | Standard Peeps (this page) | Long-winged Peeps

Standard Peeps (Semipalmated and Western Sandpipers) Figures 6-13

By far the most numerous of the peeps, both these species form huge flocks on tidal mudflats.  They prefer more open habitat than does Least Sandpiper, often packing themselves shoulder-to-shoulder in huge feeding flocks.  They feed by dropping their necks while keeping the chest well above the surface.  Their tarsi are angled back only slightly when feeding, completely unlike the deep knee-bend of the Least.  When feeding on a mudflat, they tend to plant their feet farther back and reach slightly forward with their bills.  Unlike Least, there is a large gap between where the feet are placed and where the bill is probing. (Figs. 11-12) The standard peeps are like a person bending at the waist and reaching forward to pick up something in front of them, while Least Sandpiper’s feeding style is more like someone crouching down to pick up something that is right by their feet.  Standard peeps usually seem very focused while feeding, pausing to glance around far less frequently than Least.  Though if a falcon is constantly harassing them, they may appear more cautious.  Both Western and Semipalmated show very slight primary projection, slightly longer in juveniles.  Their legs are clearly heavier than those of Least with more obvious knobby joints. (Fig 6) These two species are the only peeps with “palmations”, small webs of skin between the toes, which can be seen if you look for them, especially on birds standing on sandy beaches.

Figure 6. click to enlarge Semipalmated, Least and Western Sandpipers
From top to bottom. Semipalmated, Least, Western.  Start by comparing the two standard peeps.  Note how the Semipalmated looks compact while the Western looks lanky. The difference in bill structure is quite minimal. In this photo, head size seems more telling than bill structure. The Least is noticeably smaller than the standard peeps. The leg bones of the Least have a delicate appearance.  Compare the knee joints of all three.  Also notice how easy it is to see the presence/absence of toe webbing.  In this situation, feeding on a tilted rock, feeding postures completely change.  How would Least differ from the standard peeps in this setting? Tony Leukering 09/23/05 Avalon NJ

Semipalmated Sandpiper

Semipalmated is the dominant species of peep throughout most of eastern North America except during the late fall and winter, when virtually all depart for wintering areas in the West Indies and northern South America.  Adult Semipalmateds molt to varying degrees during migration, rarely up to 95% of their body plumage, but will very rarely show full basic plumage in the US or Canada and never molt flight feathers until they reach their winter grounds.  In late fall, first-year Semipalmated Sandpipers are instantly separated from Westerns because they maintain their brown juvenile plumage while Westerns are in gray formative (winter) plumage.  It has been suggested that Semipalmated is significantly more aggressive than Western, often engaging in intense and drawn-out physical interactions, even among juveniles (C. Wright pers. comm.). 

Figure 7. click to enlarge Western and Semipalmated Sandpiper
In this great comparison of Western and Semipalmated Sandpipers notice the head of the Semi is proportionally smaller and the underparts are smoothly rounded. To put it succinctly, the Western looks lean and the Semipalmated looks portly.  With these individuals the difference in bill shape is striking, likely a female Western and a male Semipalmated.  These adults in spring are also easily separated by plumage. When such a clear comparison is available it is valuable to spend time studying the differences in structure and behaviorBill Schmoker-Weld Co, CO 06 Apr www.schmoker.org/BirdPics

Structure

Semipalmated Sandpipers look compact, with even proportions.  Both the breast and the belly are robust so the underparts are smoothly rounded and their heads are proportionally smaller than Western’s. (Fig. 9) The species often appears bull-necked, unlike Western, which looks rangier.  Their legs appear to be placed at the center of the body, so the distribution of weight looks even. Typical bill shape is short and straight with a blunt and slightly swollen tip. However, many do not have this classic shape.  Both length and shape vary a great deal due to several variables. Females are substantially longer-billed than males. They also vary clinally, with birds breeding in the east having longer bills than western birds.  Because of this, the greatest variability is seen along the East Coast where more typically individuals may be seen alongside extraordinarily long-billed females.  In the fall, bills also vary somewhat by age, as many juvenile shorebirds attain their full bill length during their first winter, so some fall migrants will have abnormally short bills. On top of all this, add individual variation.  Semipalmateds with longer bills also have finer bill tips and the longest billed females can even show a bit of a droop, closely approximating Western Sandpiper. Individuals with the classic bill shape can be identified by this feature alone, but more often several other characteristics must be used along with bill shape.

Figure 8. click to enlarge Semipalmated and Western Sandpipers
The Semipalmated, the darkest bird, stands out clearly among the Westerns.  Why is this? The Semipalmated is still in brown juvenile plumage while the Westerns have recently completed a molt and have even gray upperparts.  Next to the Semipalmated, the Westerns look leggy and longer-necked.  The Westerns quickly become slimmer behind the legs while the Semipalmated is more substantial creating a more balanced appearance.  The partially webbed toes can be seen clearly.  The Western directly in front of the Semipalmated is an adult and the rest are first-year birds. Tony Leukering 09-23-05 Avalon NJ

Western Sandpiper

Western is by far the dominant peep on the West Coast, and Western along with Least are the only peeps likely to be seen in North America in winter.  In fall, molt timing can be a quick way to separate Western from Semipalmated.  Western Sandpipers molt much earlier, with some attaining full basic plumage by August.  Large gaps appear in the wings of adult Western due to missing flight feathers, while Semipalmated Sandpiper is unlikely to be seen replacing flight feathers in North America.  Any first-year standard peep with extensive gray, formative (winter) plumage is a Western. (Fig. 8

Figure 9. click to enlarge Semipalmated and Western Sandpipers
See how the Semipalmated, sandwiched between these two Westerns, looks compact while the Westerns look rangier.  The difference in bill structure is clear compared to the Western on the left and while it is still noticeable compared to the right-hand Western it is less obvious.  What differences in behavior would the Semipalmated exhibit as it feeds in deep water compared to the Westerns? Cin-Ty Lee Brazoria NWR, TX 05 July

Structure

Western is lanky and long-legged compared to Semipalmated. Their head usually looks slightly too large for their bodies, while the reverse is true of Semipalmated. (Fig. 7) Western appears to be carrying more weight in front of their legs which are placed slightly farther back on the body compared to Semipalmated. This creates a heavy-chested appearance that can be so pronounced that it seems surprising that they are able to stay upright. This is particularly apparent on roosting birds. (Fig. 13

While bill length does not vary clinally in Western, as it does Semipalmated, the variation between the sexes is greater.  Most, but not all, Westerns have a perceivable droop to the bill. At one extreme, many females have bills that recall Dunlin.  While some juvenile males have short bills that are absolutely straight, like Semipalmated, but are slimmer with a finer tip.

Flight and Voice

I have yet to notice structural characteristics that allow consistent separation of the two standard peeps in flight. In fall, adult Westerns are instantly recognizable by the large gaps in the flight feather due to molt.  Fortunately, both species are extremely vocal in flight and their calls are easily recognizable.  Semipalmated gives a low-pitched, rolling “chrrk” while Western gives a high, “shik” that is both sharp and squeaky with a slightly whining quality.  Feeding flocks may give these calls, but when feeding both species give a wide variety of short, sharp notes that are too variable to be consistently discernable.  

Figure 10. click to enlarge Semipalmated Sandpiper
This probably does not match your mental image of what a Semipalmated Sandpiper’s bill should look like. However along the East Coast such birds are regular and some have even longer bills.  How can we be sure this is a Semipalmated?  Look at the date on this photo.  Clearly a juvenile with no visible molt.  At this time of the year, all Westerns are well into their molt and the majority have already finish.  Note this bird looks exceptionally bulky because the feathers are fluffed up against the cold.  Cameron Cox Avalon, NJ 09 Oct


Figure 11. click to enlarge Semipalmated Sandpiper
Typical Semipalmated feeding posture (compare to fig. 12).  Chest held well above the water and the bill is reaching slightly forward.  The bill and the feet are widely spaced and the back is almost level.  Look at the blurry birds in the background.  Do they show the same shape?  Are they all Semipalmated Sandpipers?  Notice how the head of this bird is subtly more rounded and slightly smaller than that of the Western in fig. 12.  Semipalmated Plovers, like the one in the foreground on the right, often feed side-by-side with peeps and can be used as a size reference.  Least and standard peeps are noticeably smaller than Semipalmated Plovers, while long-winged peeps have clearly longer bodies. Scott Elowitz 06/03/04 Stone Harbor, NJ  www.scottelowitzphotography.com    


Figure 12. click to enlarge Western Sandpiper
Typical Western Sandpiper feeding posture.  See how it reaches forward to feed.  Note the distance between the bill and the feet, also the distance between the chest and the surface of the water.  The “knees” are only slightly bent and the body tilts forward only slightly.  Semipalmated Sandpipers feed with a similar posture  (fig. 11) but have slightly shorter, thicker necks and do not stretch as far forward. Jessie Barry San Diego, CA 06 Mar  


Figure 13. click to enlarge Western Sandpiper
All the bulk of this bird falls in front of the legs.  While Semipalmated can also appear front-heavy when roosting, the impression is rarely as dramatic as it is on Western.  Even in this position the head seems quite large.  The eye seems lost in the face.  Westerns appear to have the smallest eyes of any of the peeps, but it is subtle distinction.  Also note how square the head is.  White-rumped is the only other peep that can have such a square head. Cameron Cox- Crockett Lake, WA 27 Aug