The Zoologist/4th series, vol 5 (1901)/Issue 717/Varieties of the Dunlin, Backhouse

by James Backhouse

 

VARIETIES OF THE DUNLIN.

By J. Backhouse.

 

For several years past, when observing birds on the coast of Yorkshire, the writer has taken particular notice of what may be looked upon as our commonest Wader—the Dunlin. He has also seen the species repeatedly at its breeding haunts upon some of the highest Yorkshire "Fells," and now ventures to offer a few remarks upon the subject for the benefit of those who, like himself, know and can appreciate these common and often despised little birds wherever they meet with them. That two remarkably distinct races of the Dunlin regularly occur in Yorkshire is a fact realised by ornithologists, and by those who are habitual gunners on our coasts. The one is a strongly built bird, with long straight bill, and wings some 4¾ in. in length, found in enormous flocks, often congregating with other Waders; the other is a smaller, slighter built bird, with a shorter and straighter bill, and a decidedly shorter wing-measurement.

The latter bird is more solitary in its ways, and, as the late Mr. John Cordeaux points out, "differs from the more common species in resorting to the borders of the marsh-drains, or to the 'fittie-land' adjoining the 'muds,' in preference to the flats, and is remarkable for its extreme tameness, permitting a very close approach." This small Dunlin was described by Brehm, under the distinctive title Tringa schinzii, as early as 1822, and, as compared with certain other so-called species, is equally worthy of a separate designation to-day; for, although mere relative measurements of bill or wing may not of themselves be looked upon as sufficient to differentiate the two forms specifically, there are other reasons why the question should, we think, be reconsidered. The following illustration showing the typical heads of the respective forms is here given, in the hope that it may prove useful as showing the general pose of the bill in each case.

It is somewhat remarkable, that whereas the Dunlin seldom, if ever, exhibits any violent variation in its plumage, such as a tendency to melanism or albinism, in the smaller race alluded to we have a constant and well-marked variation from the type.

The Dunlin.—Larger and smaller forms.

Neither the late Mr. Cordeaux nor Mr. Oxley Grabham—both of whom have had practically a life-long acquaintance with the Dunlin—have known any such violent variations as are just alluded to; nothing more, in fact, than the great variation in overall markings, which presumably gave rise to the name of Tringa variabilis, as applied by Bechstein and others.

Some time ago, while collecting on the Yorkshire coast, a heavy shot brought down some Knot (buff-breasted), several Dunlin, many of them in exceedingly beautiful breeding plumage (thanks to the lateness of the season), and also a solitary example of the "drain Dunlin," which so closely resembled the Little Stint as to be mistaken at the moment for that species. The markings of the back especially, coupled with the short measurement of bill and wings, almost suggested a possible case of hybridity; such, however, we feel sure, is not the case, but the specimen in question was Brehm's T. schinzii pure and simple.

The following list shows the comparative dimensions of several specimens of both larger and smaller races in the writer's collection:—

Smaller Form.
	Bill.	Wings.
♂ Spurn, 1898⁠	0·99⁠	4·1
♂ Dunn Fell, 1884	1·1	4·2
♀ Dunn Fell„1884„	1·2	4·3
♂ Teesdale, 1886	0·99	4·15
♀ Teesdale„1886„	1·0	4·2
Juvenile, Teesdale, 1882	1·05	4·2
Adult, Ramsgill, 1886	1·2	4·5
Juvenile ♀ Ramsgill, 1886	1·2	4·3
Larger Form.
Adult, Helmsley, 1891	1·35	4·65
♂ Spurn, 1887	1·3	4·65
♀ Spurn„ 1882	1·3	4·6
♀ Spurn„ 1887	1·3	4·55
♀ Spurn„ 1884	1·4	4·75
♂ Spurn„ 1887	1·27	4·55

In the foregoing lists it will be at once noticed that all the large birds are from the sea-coast; and, oddly enough, among several specimens before us, collected on the North of England "fells" during the summer-time, not a single example of the larger billed bird is to be found, nor can we recollect having seen any but the smaller race upon these "fells." The question then seems to resolve itself, first of all, into a distributional one as to the breeding of the two forms; that point settled, we shall surely come one step nearer to a satisfactory basis upon which to establish the validity or otherwise of Tringa schinzii as a species. The writer has now been fortunate in discovering what may well be looked upon as "headquarters" for Yorkshire breeding Dunlin, and it is to be hoped that during the coming season careful observation can be made upon a large number of nesting birds.

Meantime the evidence of two well-known north-country ornithologists must now be given as bearing in an important manner upon the subject at issue.

In a letter, dated Jan. 30th, 1899, Mr. Harvie-Brown writes as follows:—"The short, straight-billed form breeds very abundantly in the Outer Hebrides; also in Tiree and elsewhere in the west and north, where I have taken their eggs. Here also, within five miles of this house (Larbert, Stirlingshire), in two localities, the short-billed form is found nesting; I had their eggs here several seasons, and can always go to their nesting-ground any season. In Sutherlandshire I have taken a few Dunlins' eggs. The birds appeared to me to be larger than the Hebridean birds, but not so large as others which I have shot on the Firth of Forth, where, however, I have, during the prevalence or after a sharp change of wind, also shot the small form. If we have an east wind blowing at Grangemouth, or between that and Kincardine, which continues any length of time, our coast becomes bared of almost all the big flocks of Dunlins. But at such times small trips of perhaps two, three, four to six may be seen, and these are almost invariably the small short-billed birds. Or if a west wind has prevailed for long (and that is our best wind for shooting the shore-birds on our coast) immense flocks of Dunlins are found—thousands strong; on one occasion I fired two barrels into a huge flock upon Grangemouth breakwater,.... and picked up sixty-seven;.... but of all these not one was a short-billed bird. But if the wind suddenly went round from west to east, these big flocks flew right away across to the Fife shore; and if the wind continued twenty-four hours in the east, then we would begin to pick up the short-billed birds, apparently in family parties. My own belief is that these birds come across from 'Clyde' to 'Forth,' with (or rather against) the change of wind."

Again, in a letter from Dumfries, Mr. Robert Service states: "A good many pairs nest along the merse-lands west of Southerness Point, and these certainly belong to the small-bodied and short-billed race, if race it be. I always think their summer plumage is not so deep or bright as the others that, at that time, are still flying along the sands in great flocks, and that even till the end of May are to be seen or heard flying northward to further breeding quarters."