Great Egret

Great Egret

Thursday, 24 November 2016

Peep conundrum and other late autumn shorebirds

Birders will be aware of the recent conundrum surrounding a small peep seen at the Blenheim Sewage Lagoons in the last couple of weeks. Peeps, for the benefit of non-birders, are those smaller shorebirds of the genus Calidris, and are sometimes difficult to identify to species due to their general similarity as well as their various stages of moult which seem to overlap.

Peeps are fairly rare as the autumn progresses. Certainly by late October and early November, any peep is quite rare in southern Ontario. Indeed, the majority of them have made their way to South America! So the presence of a peep at the sewage lagoon, mixed in with larger, more distinct shorebirds known as Dunlin, was out-of-the-ordinary to say the least.

One of my first shots of this peep, between two Dunlin
Two of the 40+ Dunlin present Nov 18, 2016

Steve Charbonneau was one of the first to notice this peep at the lagoons during his almost daily visits there.
Steve C on the prowl for birds at the Blenheim lagoons

There are a number of useful birding references that we used to attempt to sort out this bird:
-Sibley Guide to Birds (Sibley)
-Advanced Birding (Kaufman)
-The Shorebird Guide (O'Brien, Crossley and Karlson)
-Shorebirds: An Identification Guide (Hayman, Marchant and Prater)

In addition to using these references, other birders got photos of various angles and in various light. Some of these photos were sent off to other birders, most of whom had more experience with these peeps than Steve and I had.

What follows does in no way attempt to consolidate all the detailed information found in these references pertaining to these two species!

Given the subtle differences, and decent but perhaps less than ideal views, it was first called a Semipalmated Sandpiper (SESA). SESA are some of the most abundant smaller shorebirds in eastern North America. Now had some of us, myself included, clued in to the fact that SESA are almost unheard of anywhere on the North American continent this late in the season, we might have given it a bit more careful scrutiny. We certainly had entertained the thought of it being a Western Sandpiper (WESA), which is one the most abundant smaller shorebirds in western North America, but not seen very often in the east. But in spite of our considering WESA, some of the features didn't seem quite right.

For example, WESAs have a longer, finer tipped bill than the shorter, somewhat chunkier bill of a SESA. In addition, the bill tip of a SESA is often slightly enlarged, not finely tipped, and the bill of a WESA usually has a slight droop to the tip.

Peep on the right has a slightly bigger tip?
bill doesn't have much of a drooping tip, if any
Complicating this 'bill' issue is that the bills of females are typically somewhat longer than that of a male, and there is some overlap even between the species. Even at that, the comparative length differences is a matter of millimetres. So using the bill characteristics is not all that reliable.

The shape of the head is marginally different, with some field guides suggesting that a SESA is more rounded compared to a slightly more squarish look to the head of a WESA.

WESA is slightly slimmer and longer looking than a slightly chunkier looking SESA. Of course given the time of year and the relative cold temperatures (it got below freezing on more than one occasion, and ice had formed around the edge of the cells), perhaps the bird was cold and has fluffed up its feathers, given the appearance of being a bit more chunky looking.

Since WESA have slightly longer legs, they are more often found feeding in deeper water, often belly deep, compared to SESA which is more likely to be found in shallower water and closer to the edge. There is some variability, of course. This bird seemed to stay in shallower water than the larger Dunlin, however.

What might have been especially helpful is having one of each species side by side, since the differences are somewhat relative, and this bird was only in the vicinity of the much larger Dunlin.

Dunlin and presumptive WESA
Dunlin and presumptive WESA
Moult is important to consider. The young WESA apparently begin their moult as early as August, even when they are on their breeding ground before they head south, whereas young SESA often do not moult much until they get to their wintering ground in the southern hemisphere.

SESA August 24, 2016
SESA, Sept 4, 2016
And that leads us to the feature that perhaps was the deciding factor in the consensus of this bird being a WESA. Under certain light conditions, especially in close-up views, there is a slight but distinctive rufous colour on their scapular feathering. SESA does not have this rufous colouring this late in the season.
A bit of rufous on the scapulars
So given all of the above, it seems the collective opinion of this bird is that it is a WESA. Some field guides state that distinguishing a winter WESA from a winter SESA is one of the more difficult birding challenges, and that certainly was the case with this bird.

Check out Blake's blog for some additional details as well as some of the November and December records of WESA in Ontario.

When trying to ID this bird, I even spent a bit of time trying to determine if it was one of the other even rarer small Calidrids that are Asiatic in range, but have been recorded in North America on extremely rare occasions. The two closest in appearance would be the Red-necked Stint and the Little Stint. One of the most distinct differences, if it is visible, is that the two latter species do not have any webbing between their toes, whereas WESA and SESA both have some webbing. I noted that one of my photos showed the feet and webbing, so I could not make this into a Calidrid from Asia!

Other shorebird species can linger or even turn up in November. As mentioned earlier, Dunlin are around, and more than 40 were seen accompanying the WESA a few days ago. The colder weather in the last couple of days seems to have encouraged them to move on, as only half a dozen or so were seen earlier today.

One rare but regular shorebird that always attracts attention is the Purple Sandpiper. It is a medium-sized, dark and chunky shorebird that shows up in late fall. I had been looking for them at Erieau on Tuesday of this week, but was not successful in finding any. Yesterday morning, I got word from Jim Burk that one was seen at the pier at Erieau. Unfortunately I had to go off to Burlington and would not have a chance to look for it yesterday. When I got home in the evening, I discovered that several birders were able to get some excellent close photos of this species, and in at least one case, actually captured two of them in one image.

Check these out:
Garry Sadler's ebird list and image here.

Steve Charbonneau's ebird list and images here.

Today, Thursday, I made a point of heading to Erieau. Unfortunately the first couple of hours were unsuccessful in finding this species. There were several other birders in the area looking as well, and we did console ourselves with decent looks through the 'scope of the bright male Harlequin Duck that has been around the rocks on the far side of the breakwall for a few days. The other birders eventually left, but since I didn't have anything pressing, I drove over to where the fish tugs often are moored, as it gives a better angle of view to the rocks on the east side of the breakwall across the main channel. I scanned back and forth for awhile through the 'scope, and all of a sudden a Purple Sandpiper hopped up on a rock in excellent view but only for about three seconds before dropping down, not to be seen again. So no photos this day. This next photo is a scan of a slide that I was able to get of a very cooperative Purple Sandpiper back in my film days. It was taken on the main pier heading out into the lake.

With the relatively mild weather continuing, it is only a matter of time to see if any of these shorebirds are around for the Blenheim/Rondeau Christmas Bird Count less than a month away. Over the years, I have had about 10 species of shorebird in my area, so I am hoping for some shorebird activity!

No comments:

Post a Comment