White-backed Duck Behaviour 71 The behaviour of the White-backed Duck A. C LARK Introduction up instantly when a Marsh Harrier Circus These observations on the White-backed ranivorus flies near, or move away from Duck Thalassomis leuconotus were under­ an approaching Coot Fulica cristata. taken to check and extend those which Maccoa, Southern Pochard Netta erythro- Johnsgard (1967) made on captive birds, phthalma and Red-billed Pintail Anas because of the apparent lack o f informa­ erythroryncha have also been seen tion on this species in the wild. They amongst the White-backed Duck. Often were made on ducks which were present when disturbed from their sleep the latter for varying periods at three dams and one push their heads up and will often Wing- natural pan situated in the vicinity of the flap. The sequence, Nibbling - preen, Witwatersrand, Transvaal, South Africa. Shake and Wing-flap is not unusual at The waters were relatively shallow, with this time and Leg-wave, Wing-and-leg- maximum depths varying from two to six stretch and Head-scratch may also be seen. feet. Although sedges and other aquatic The break up of sleeping parties takes plants provided suitable nesting sites, no place gradually. Single birds or small breeding took place during the period of groups will leave and go on their way to observation, i.e. July 1968 to April 1969. feed. Flights just above the water surface The names of the various comfort move­ for distances of ten feet to fifty yards are ments described are taken from M c­ occasionally taken. There are often short Kinney (1965) and for the movements swimming movements with little apparent associated with threat and copulation the purpose. These involve direction changes, names are taken from Johnsgard (1967). movements away as though avoiding, movements towards as though asserting Resting or sleeping and much pausing with head partly raised and held stiffly. The birds rest or sleep on the water in groups, invariably with the beak tucked Feeding into the scapulars, the distances between individual birds varying from one foot to The White-backed Duck feeds by diving two yards. At such times the tail is incon­ to the floor of the water and sifting food spicuous but sometimes it is raised slightly from the mud or debris resting there. off the water. At Spaarwater where the Although Clancey states the birds dive greater portion o f the water surface was with a leaping action and Johnsgard con­ choked with mats of grass stalks and firms this, all the Whiteback under obser­ other aquatic plants, they preferred this vation made a smooth plunge like the area and were never seen very near the Maccoa except that the birds made a shore nor resting in open water. This splash dive when avoiding a Coot. The seems to be the general pattern, but at Fulvous Whistling Duck Dendrocygna Impala Park they had to move very close bicolor lifts part or the whole of its body to the shore to get anchorage of this type clear of the water when diving but may and would sometimes sleep in open water frequently feed by ‘ up-ending.’ The where, like the Maccoa Oxyura maccoa, Whiteback does not move far laterally they would drift in the wind. Although under water when feeding. In water Clancey (1967) states that Whiteback approximately one foot deep I have re­ repair to dry land for rest, I would con­ corded 12-14 seconds under water and sider this exceptional for the study area. 4-6 seconds between dives above. At Frequently a bird may be seen sleeping Spaarwater where the depth was two to with one expanded webbed foot visible, three feet, time under water varied from sometimes with both feet sticking out on 15-20 seconds, time on surface from 5-10 either side like fins, and this habit may seconds. At Tweefontein Dam where the explain their preference for the anchorage water had an estimated depth of six feet, provided by stalks of aquatic plants. I recorded 25-30 seconds under water and During the daytime most birds sleep for 7-12 seconds above. Feeding from the sur­ three to four hours in the late morning face is unusual. The times under water with casual shorter spells at other times. agree closely with those given by Johns­ The greater part o f the day is spent gard but he gives a more extended period sleeping, giving the impression that the on the surface between dives. birds are inactive. Although they are Whilst on the surface between dives I apparently sleeping, they push their heads have seen birds tread water, the feet 72 Wildfowl pushing water downwards, not backwards than exercise, take place at from 5-30 feet as when swimming. This behaviour is and the birds keep over the water. evidenced in the slight rocking movement T w o typical instances of pre-flight be­ of the body and the movement of the haviour were recorded as follows : ‘ Six surrounding water. As a result of the birds swam off in single file. After a short treading action the body is lifted notice- distance they mostly turned to face the ably and the breast prominentiy displayed. wind with heads up. There was a pause The treading continues until the birds and I saw one bird Shake and two Wing- dive again and it is possible that they flap. After another pause I saw one lateral behave in this way when they are feeding Head-shake. There was another brief in rather shallow water, the slight lift of pause and they all flew off and did a the body facilitating the dive. figure-of-eight over the pan.’ ‘ T w o birds As the water level at Spaarwater drop­ with heads up faced the wind. They ped, the birds occasionally fed where the turned and swam with the wind. After a surface water was matted with grass. Here short distance they turned to face the they had to struggle to surface properly wind, hesitated and then swam again with and sometimes the head only came out. the wind. They repeated this movement Before diving again they would lower the a third time before facing the wind to beak on to the breast. Occasionally when take off.’ a bird surfaces it carries a string of weed It is evidently important for the White- in its beak which it makes no attempt to back to have a good stretch of water in swallow. Sometimes the head is blackened front before attempting to fly. I have seen by debris the bird has stirred up in feed­ a bird swim 100 yards with the wind to ing. At Spaarwater Coots frequently fed enable it to get into a position to take off in the wake of a diving bird. into the wind. The Head-shake is not The main observed feeding times are often used and when it is, is not neces­ from dawn to shortly after sunrise and sarily repeated by other birds in the in the late afternoon until sundown. At group. Pre-flight behaviour is mainly Spaarwater they mainly chose the areas recognised by birds gathering, hesitating where the surface water was free of vege­ with their heads up and facing into the tation and the birds joined together in wind. Flight is not always simultaneous. groups of varying sizes. Once feeding Quite frequently after flight I have seen commenced the birds continued steadily birds rest with beak in scapulars. and some fed for 60-80 minutes without a break. Sometimes they would cease for Voice a period and then continue feeding. The main call of the Whiteback consists of a double note which sounds like ‘Tit-weet,’ Flight reed-like, with the second longer note The Whiteback seldom flies during the lower than the first. When on the water day and when it does, like the Maccoa, the bird puts its head right up to call. it has difficulty in getting airborne and Single birds may call between dives, or paddles the surface for 10-20 yards before during a pause in swimming or during a rising clear. For this reason it usually takes break from sleep, but occasionally others off into the wind and prefers windy days. will join in. The call is sometimes given Its wings beat steadily and it appears to during a take-off, during flight or immedi­ have little manoeuvreability. It flies with ately after coming down on water. The legs to the rear protruding beyond the double note is often repeated several tail. Before landing, its legs are lowered times and I have heard one bird repeat and the webs of the feet fanned out, as the call at intervals over a period of 50 if as air brakes, before being moved for­ minutes when it seemed to have no signal ward to take the impact of the water. value. It is also sometimes heard after Even so the bird usually ploughs into the disturbance occasioned by people or an water with its breast. I have not seen them aggressive approach of another bird. The come down on land. ‘ Tit-weet ’ call carries well and can To reach another bird, or to feed, some readily be heard at a distance of 100 take short flights of ten yards just skim­ yards or more. Johnsgard also records a ming the water or longer flights in a ‘ conversational ’ or contact call consisting direct line at a height of approximately of three to five notes uttered on a rising four feet. Protracted flights of a more series of soft whistles.