Studies of Avocet behaviour

P. /. S. Olney "Photographs by W. H. van Schieveen and Eric Hosking

Plates 32-39

The accompanying photographs admirably illustrate various facets of the behaviour of Avocets Kecurvirostra avosetta. The following notes are based on the work of Makkink (1932, 1936) and Brown (1950) and on my own observations at Havergate, Suffolk, and in France and the Netherlands.

Grouping

Plate 32 shows some of the characteristic aggressive behaviour of Avocets which often, though not always, precedes fighting. These behaviour patterns are basically a series of postures, movements and vocalisations which serve as threats. They tend to repel or intimidate the opponent and sometimes lead to actual combat. They may take place on land or on water.

The first distinguishable movement is the gathering together of more than two Avocets into a group. These groupings are not chance meetings, but are deliberate encounters in which the birds form a rough circle with their heads towards the centre (see especially plate 32c) and their bills lowered almost to or just below the surface. Within the group the Avocets may stand quite still for a short time or they may move forward slightly. A common behavioural component at this stage is for the birds to move their feet and bills up and down in a bowing movement. This movement may be interrupted by peck­ing at objects or picking them up and throwing them aside with a slight jerk of the head. The bowing is often accompanied by a weak and rapid call—'cwit, cwit, cwit . . . '—which tends to become more excited as a two-note call—'c-c-c-creewer . . . '. Bowing is not only a common element in aggressive behaviour, but is also seen during parental change-over at the nest and as a primary nest-building activity.

The number of Avocets in a group may vary from three to 15, and very occasionally up to 18 are seen together. On one occasion in the Netherlands in May I watched 16 gather into a circle and a series of spectacular bowing movements occurred, followed by some stylised fighting. In this group six definite pairs could be distinguished. Usually it is comparatively easy to distinguish pairs, for they tend to keep close together and often they will copulate before entering

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the group or after leaving it. Within the group, even if separated, the two birds quickly come together again and constantly keep side by side.

Normally there are a number of movements preceding any actual contact. The Avocets walk toward one another with their heads stretched out horizontally or slightly upward and with their wings held just away from their bodies. They move forward and around each other rather carefully and slowly. Then suddenly one may spring forward with unfolded and flapping wings (plate 33). Usually the opponents move quickly away. Though the wings play an important part in the attack, the legs and bill may also be used. The attacker may leap on to another bird and may peck or pull at its neck and body. Usually it is merely a stabbing movement, but occasionally one Avocet will hold on to another. Little damage ensues from these attacks and the individual which is being attacked usually moves quickly away, often jumping sideways to avoid the flick of the other's wings. Occasionally one flies away and is chased by a would-be attacker uttering 'kluut, kluut' notes. Normally this is followed by the Avocets dispersing or regrouping.

Often during these encounters individuals will follow each other around with their necks drawn back, their bodies in a horizontal position and their heads held slightly downwards. Occasionally birds from a group will also take to the air. Then the attacker will closely pursue its opponent and turn away only just when it seems as if contact is imminent.

Two strange pieces of behaviour often occur during these aggressive movements. In the first, one or more of the Avocets may suddenly sit down; once seated, they usually begin to peck or pull at surrounding objects and then just as suddenly they get up and move back into the conflict. In the second, one or more of the birds may suddenly assume a sleeping position with the bill tucked below one wing. This often occurs just before or even during an attack and may forestall actual contact. Sometimes, however, it is the attacker which suddenly takes up this attitude that Makkink (1936) called 'pseudo-sleeping'. The position differs from ordinary sleeping in that it is kept up only for a very short time and normally both the bird's legs remain on the ground.

What is the biological significance of these groupings with their aggressive components? Mainly they seem to be a method of strengthen­ing the pair bond. The groupings occur before nest-building and while eggs and young are present. They may take place away from obvious territories and therefore away from eggs and young. The bond appears to be strengthened by the constant coming together of the pair within the group, by their mutual bowing, and by the mutual attack on other Avocets.

208 Studies of Avocet behaviour

Attacking intruders

Intruders into nesting or feeding territories are usually subjected to some form of intimidating or attacking display. Other Avocets and other birds, especially Shelducks Tadorna tadorna, are frequently harassed by territory-holding parents (plates 34-35). Usually no real contact takes place and the intruder is merely pursued and disturbed enough to make it go away. Normally the attack begins with a typical warning posture, in which the head is held forward and downward and the wings slightly away from the body (plate 34a). Moving forward in this posture or edging toward the intruder may be enough to intimidate the latter to move away. Sometimes, however, an aerial wing-flapping attack follows, in which wings, legs and bill may be used as weapons (plates 34b and 35).

Occasionally an intruder, especially one at close quarters, produces an apparent conflict in the parent Avocets between the motive to re­main close to the nest or chicks and the impulse to escape. A com­promise behaviour pattern appears to have evolved which is basically a ritualised threat leading often to a distraction display. Smith and Hosking (1955) have well described and illustrated such situations. As an intruder approaches the nest or chicks, one or occasionally both parents will fly around calling excitedly and diving down repeatedly, swerving away just before contact would be made. If this fails to deter the intruder, one of the birds may alight in front of, and run towards, the intruder and begin a threat display. This is the same posture as is often adopted by a sitting Avocet when confronted by an intruder (plate 39). The tail is cocked up, the wings are spread (showing clearly the black and white markings) and the bird repeatedly calls 'creewer, creewer . . . ' . The wing tips are drooped almost to touch the ground and may even spasmodically hit the ground with a comparatively loud noise. The bird may move backwards and forwards or mark time with its feet straddling the nest or chicks (plate 39a). This posture may be adopted a number of times, with intervals in which the bird flies up and repeatedly dives at the intruder, or may lead into a dis­traction display in which it moves away with one wing trailing along the ground.

Sexual behaviour

Precopulatory display begins with both of a pair of Avocets preening. Brown (1950) called this 'false-preening' to distinguish it from the less vigorous and less exaggerated normal preening behaviour. Precopulatory preening has the same behavioural components as normal preening, though it is often, but not invariably, interspersed with water pecking and splashing. In preening, the bill is passed through the feathers, beginning near the rump and working into the wings and body, with the head being frequently rolled over the

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plumage. The feathers are ruffled up and shaken, often with some stretching of the legs and wings.

Copulation always begins with the female suddenly lowering her head and neck to the water surface (plate 36). In this stance she will remain almost motionless, though occasionally she will make inter­mittent movements of the head from side to side as in feeding. The male still vigorously preening and water-splashing moves close to the female's side (plate 36a); he then moves behind her to the opposite side and continues with his exaggerated preening movements. The female remains still, though as the male moves she may turn her head and feet slightly in his direction. The male continues to preen on alternative sides of the female for a variable time, and he may change sides many times before coition occurs. The male of a pair on Haver-gate was seen to change sides 25 times over a period of 48 minutes before attempting to mount the female. This was exceptional and during 50 observations of copulation the number of side changes varied from three to 16.

The male then suddenly jumps up sideways on to the back of the female and with his wings outstretched sinks down on to his tarsi; his bill is slightly open, though no sound is heard (plate 37). She usually moves her head from side to side in a wide arc. Immediately after coition the male drops sideways into the water. From the moment he mounts her to the moment he moves back into the water takes only a few seconds. The birds, now separated, hold their wings slightly away from their bodies and move forward with crossed bills (plate 38a). They then move away from each other (plate 38b), either to resume feeding or to begin false-preening again. It is not uncommon for a pair of birds to undertake the complete sexual display again within a few minutes.

The sequence of events described above is not always so clear-cut, and often some of the actions are missing or suppressed. Though it is quick, the behavioural components are easily distinguishable and together they form a beautifully stylised display which is a wonder to behold.

REFERENCES

BROWN, P. E. 1950. Avocets in England. R.S.P.B. occasional publication no. 14. London.

MAKKINK, G. F. 1932. 'Einige Beobachtungen uber die Paarungsbiologie des Sabelschnabels (Recurvirostra avosetta L,)\ Ardea, 21: 38-43.

1936- 'An attempt at an ethograrn of the European Avocet {Recurvirostra avosetta L.), with ethological and psychological remarks'. Ardea, 25: 1-62. plates

SMITH, S., and HOSKING E, 1955. Birds Fighting. London, pp. 105-109 and 30-31.

P. J. S. Qfoej, The Zoological Society of London, Regent's Park, London NWI

P L A T E 32. Avocets Kecurpirostra avosetta grouping, Netherlands, April 1968. Three to 18 meet in a circle with heads inward. Bowing movements, pecking at objects and special calls and postures lead to actual attack (plate 33). Grouping strengthens the pair-bond; coition often follows (pages 206-209) {photos: W. H. van Schieveeri)

P L A T E 33. Avocets Recurpirostra avosetta attacking during grouping, Netherlands, April 1968. Suddenly one leaps with flapping wings at a bird of another pair. The latter usually moves away, but the aggressor may land on it, striking at it with legs and wings and stabbing with the beak (page 207) (photos: W. H. van Schieveen)

P L A T E 34. Avocets Recurvirostra avosetta attacking Shelducks Tadorna tadorna, Neth­erlands, May 1969. Normally the warning posture above, with head forward and wings held out from the body, discourages the intruders, but sometimes an aerial attack mav follow, as shown below and on plate 3 5 (page 208) {photos: W. H. van Schieveen)

P L A T E 35. Avocet Kecurvirostra avosetta making aerial attack on Shelduck 'Tadorna tadorna, Netherlands, May 1969. Wings, legs and bill are all used as weapons (page 208). Avocets harass birds of many other species which enter their territory, but seem especially to resent Shelducks (see also plate 34) {photo: W, H. van Schieveen)

P L A T E 36. Precopulatory display of Avocets Kecurvirostra avosetta, Netherlands, April 1969. Both birds 'false-preen'; then the female lowers her head and neck and stands almost motionless, while the male continues preening on one side of her and then the other, often switching many times (page 209) (photos: W. H. van Sckievsen)

P L A T E 37. Copulation of Avocets Recurvirostra avosetta, Netherlands, April 1969. After the preening at each side of the female (plate 36), the male jumps sideways on to her back and with wings stretched and mandibles parted, sinks down upon his tarsi; she moves her head from side to side (page 209) (photo: W. H. van Schieveen)

P L A T E 38. Post-copulatory actions of Avocets Kecurvirostra avosetta, Netherlands, April 1969. After coition the male drops sideways into the water and the pair then run forward with bills crossed and wings held out from their bodies before moving apart with a characteristic crouching gait (page 209) {photos: W. H. van Scbieveeri)

P L A T E 39. Threat displays by Avocet Reairvirostra avosetta at nest, Netherlands, May 1952. A human intruder at close quarters (note the hand below) may produce a conflict between attack and escape. With tail cocked and spread wings drooped, the bird moves back and forth, and calls repeatedly (page 208) {photos: Eric Hosking)