55 the Distraction Displays of the Little Ringed Plover and Territorial Competition with the Ringed Plover

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THE DISTRACTION DISPLAYS OF THE LITTLE RINGED PLOVER AND TERRITORIAL COMPETITION WITH THE RINGED PLOVER. BY EDWARD A. ARMSTRONG. THE distraction displays of the Little Ringed Plover (Charadrius dubius) bear a general similarity to those of the Ringed Plover (Charadrius hiaticula) (Williamson 1947) and Kentish Plover (Leucopolius alexandrinus) (Simmons 1951). The following observa tions are based mainly on the behaviour of a pair with small chicks in East Anglia. It was not possible to study the forms of display throughout the nesting cycle so these notes are necessarily incomplete. As the behaviour of the birds with the brightest plumage was consistent with their being males they are referred to as such. The principal display-patterns observed were (1) the crouch- run, (2) the squat and (3) injury-simulation. The sense in which "injury-simulation" is used is indicated elsewhere (Armstrong 1949).

(1) THE CROUCH-RUN. The first reaction to an intruder of a bird on the ground consisted of running away with the body held low. It was most characteristic of the female. As performed by some other waders this has been styled the "rodent-run" (Williamson 1950). Although Selous (1927), writing of such behaviour by the Kentish Plover, describes the bird as looking rather like a rat the term "crouch-run" used by Simmons when referring to this species seems more suitable as it avoids raising the question of the degree of similarity between the appearance of bird and mammal. The Golden Plover (Pluvialis apricaria) and, to a rather lesser extent, the Ringed Plover, and even less the Little Ringed Plover, act during the crouch-run in such a way that one has the impression that the bird is being inconspicuous conspicuously.' Their behaviour seems to be, not simply retreating in the manner best adapted to evade observation, as a Corn-Crake (Crex crex) will run with head and neck depressed through low herbage looking like a small quadruped, but a form of distraction display. A little evolutionary modification may transform escape move ments into diversionary activity. It is perhaps, impossible to make a rigid distinction between behaviour such as the Corn-Crake's, which is purely an escape reaction, and the crouch-run by other species which functions as distraction display, but during the latter the bird is apt to appear occasionally where inequalities in the ground would enable it to remain con cealed and to look around from time to time. As the term "mobile lure-display", used by Simmons to describe another form of display, would include the crouch-run and other types of 56 BRITISH BIRDS. [VOL. XLV. behaviour its employment in this connexion is ambiguous and confusing. Similarly his term "static lure-display" does not aptly denote the incapacity-simulation display which he describes nor discriminate it from other forms of display to which it might be applied.

(2) THE SQUAT. After running a short distance either male or female may squat, but the male's attitude is peculiar, for his head and body are held low but his stern is often raised and he is apt to make odd little shifting or turning movements. The male Ringed Plover performs in a similar way, as shown in one of my photographs (Armstrong igsob). It is difficult to decide whether the net effect is to conceal the bird or render him more conspicuous as much depends on the nature of the terrain. The posture seems to be distinct from displacement-brooding though it bears some super ficial resemblance to it. Probably it has a threat function. A crouching attitude when menaced is characteristic of many birds.

(3) INJURY-SIMULATION. After the crouch-run the Little Ringed Plover commonly squats, frequently in a hollow or rut, and begins flicking its wings; first a quick wing-flip, then another, gradually warming up to realistic injury-simulation with first one pointed wing raised high, then the other, and so on, sometimes spread-eagled with both wings on the ground. Neither of the birds was seen to flounder forward, then pause with flapping wings and flop with both wings outspread as a Ringed Plover, disturbed at the nest, will do, though a wing-flip or two may precede the performance. Like the Ringed Plover the Little Ringed Plover manages to keep an eye on a human intruder while engaged in this form of distraction display. When I was the occasion of it the display was never enacted nearer than 25 yards. Although the bird rendered itself highly conspicuous, exposing a remarkable amount of white plumage and constantly uttering clinking notes, yet at this distance a mammalian predator probably would not have seen it and a human spectator without binoculars could scarcely have recog nized it. When the bird performed in a hollow the under-side of the expanded tail was exposed. The dark markings on the white feathers constituted a strikingly conspicuous and beautiful pattern. This incapacity-display sometimes continued for a minute or longer while the bird spasmodically flapped in the chosen hollow; then it would run on and start performing again. I have not noticed such prolonged injury-simulation in one spot by a Ringed Plover. A fragment of epigamic display was seen. With tail fanned the male flew near to where the female was feeding and uttered a high, sweet trill before alighting. VOL. XLV] DISPLAY OF LITTLE RINGED PLOVER. 57

As an incidental matter of interest it may be mentioned that one bird was seen to spend some minutes pecking at a large dragon-fly.

TERRITORIAL RELATIONS BETWEEN LITTLE RINGED PLOVER AND RINGED PLOVER. There was constant quarrelling between the Little Ringed Plovers and the male of a pair of Ringed Plovers. The latter frequently flew near to the Little Ringed Plovers and often both the smaller birds would fly at him. There would be a flurry of fawn and white plumage, but in spite of the vicious darts made at him it is doubtful whether he was ever actually struck. At the height of these attacks the Little Ringed Plovers uttered a high chirruping or hinny—apparently a higher-pitched version of the whistle which Ringed Plovers utter when attacking. On such occasions the threat display of the Ringed Plover consisted of fluffing the feathers on head, neck and breast while the body was held at a slight angle, the wing opposite the Little Ringed Plover being somewhat raised and the partly-expanded tail held rather obliquely so that its markings were visible to the attacker approaching from the side. The tail was not depressed acutely or trailed as in the injury-simulation display and, sometimes, during threat display. The posture bore a vague resemblance to the beginning of injury-simulation. The Little Ringed Plovers also enlarged their contours by fluffing the white plumage, including the body feathers. I have suggested (1950 c) that the injury-simulation of the Ringel Plover and Killdeer (Oxyechus vociferus) incorporate elements from the threat and courtship displays. Probably this is also true of the Little Ringed Plover's injury-simulation display. Sometimes the male Ringed Plover would pursue the (presumed) male Little Ringed Plover by stages, though the procedure was more like following than pursuing. When the Ringed Plover alighted the Little Ringed Plover would squat a few feet ahead, the Ringed Plover would run past a foot or two and the smaller bird would again run ahead, perhaps giving a flip of his wings, and squat again. So they would proceed until they reached the boundary of the Little Ringed Plover's territory ; then the latter would fly back with the Ringed Plover in pursuit and the pro cedure would begin all over again. Once during this curious progress, when the Ringed Plover was obviously in a state of tension, he raised and shook his plumage—a common displacement- activity in this species (and others) (Armstrong 1950a). Imme diately the Little Ringed Plover, which had been squatting, flew at him. Sometimes during these territorial disputes the Little Ringed Plover's squatting developed into injury-simulation, either a mere a-synchronous flipping of the wings or the full performance 2-3 feet from the Ringed Plover. The latter would follow and the 58 BRITISH BIRDS. [VOL. XLV. Little Ringed Plover would move on, creeping, crouching and injury-simulating until the boundary was reached and the birds returned. The male never did anything more interesting than squat when I approached him. Two days later the Ringed Plover, which had then three small chicks, was frequently seen chasing the Little Ringed Plover in flight, sometimes flying around the area in which both families fed for more than five minutes at a time. They flew fast, the Ringed Plover following every dart and swerve of the Little Ringed1 Plover. Once when both had alighted the male Little Ringed Plover squatted but the Ringed Plover dashed at him before he could begin his incapacity-display. The Little Ringed Plover was silent most of the time during the chase but occa- sinally uttered whistling notes. A chittering call was also heard, apparently emanating from this bird. In spite of this continual friction, which occupied a great deal of the birds' time, the Little Ringed Plover reared young success fully, and doubtless the Ringed Plovers were also successful. Thus the situation provided an illustration of territorial alterca tions between closely related species with somewhat similar ecological preferences, one larger and more powerful than the other with the advantage of being resident and so of being able to establish territory before the other arrives, the other a smaller summer visitor, yet neither succeeding in preventing the other competitor from breeding.* However, a few hundred yards away the relationship between the two species was puzzling. In a Little Ringed Plover's territory there was an apparently deserted clutch of three Ringed Plover's eggs, yet there was no sign that the Little Ringed Plovers had' eggs or young. Once or twice they both flew around high up as if the male was chasing the female.

Both sexes of the breeding pair of Little Ringed Plover acted sentinel, but the male appeared to spend more time acting in this capacity than his mate. He would spend as long "as 15 minutes on the look-out perched on his right leg on a vantage-point, but his alertness may have been accentuated by the state of tension which existed between the two species. Ringed Plovers will shelter their fledged young under their bodies as they perch on the ridge of a shingle bank or hillock where they can have a wide view and perceive approaching intruders; this appears to be the customary way for an adult with small chicks to spend the night. The manner in which Little Ringed Plovers were seen with chicks around them on a shingle bank suggests that they may roost in the same way.

SUMMARY. VOL. XLV] DISPLAY OF LITTLE RINGED PLOVER. 59 Forms of display by a pair of Little Ringed Plover with chicks are described' and an account is given of territorial altercations with a Ringed Plover, which did not prevent successful breeding.

REFERENCES.

ARMSTRONG, E. A. (1949)- "Diversionary display." Ibis, xci: 88-97, 179-188. ARMSTRONG, E. A. (1950 a). "The nature and function of displacement activities." Symposia Soc. Exp. Biol., iv: 361-384. ARMSTRONG, E. A. (1950 b). "Photographs of the complete series of the Ringed Plover's 'distraction display'." Illust. Lond. News, ccxvii: 219. ARMSTRONG, E. A. (1950 c). "Counterfeit terror." Animal Kingdom, Iiii: 11-15. SELOUS, E. (1927). Realities of Bird Life. London. SIMMONS, K. E. L. (1951). "Distraction-display in the Kentish Plover." Brit. Birds, xliv: 181-187. WILLIAMSON, K. (1947). "The distraction display of the Ringed Plover." Ibis, lxxxix: 511-513. WILLIAMSON, K. (1950). "Interpretation of 'rodent-run' display." Ibis, xcii: 28-33.

*Mr. K. E. L. Simmons has drawn my attention to the observations of S. Durango (Fauna och Flora, 1943: 145-154) who gives two records of Ringed Plovers taking over Little Ringed Plovers' nests containing two eggs and laying their own c/4 in them,