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Activity and Time Budget of Tufted Ducks on Swiss Lakes During Winter JEAN-CARLO PEDROLI

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Activity and Time Budget of Tufted Ducks on Swiss Lakes During Winter JEAN-CARLO PEDROLI Activity and time budget of Tufted Ducks on Swiss lakes during winter JEAN-CARLO PEDROLI Introduction Description of Lake Neuchâtel Alternation of day and night produces a Lake Neuchâtel (Figure 1) belongs to the change of activity for most living organisms great lake region of central Europe, which adhering to a rhythm and following a regu­ was once covered by alpine glaciers. Its lar pattern. Changes in the other environ­ coordinates are 46°53'N and 6°51'E and mental conditions were shown in the case the altitude is 429-3 m above sea level. of ducks by Nilsson (1970) and Tamisier With a total length of 38-3 km and a maxi­ (1972) to produce only minor alterations in mum width of 8-1 km, it is the largest the activity pattern, alterations which it is subjurassic lake. The surface is 214-6 km2, important to know in order to determine a the mean depth 64-2 m and the maximum habitat’s quality. When the activity rhythm depth 153 m. There is a large littoral zone is altered too much by environmental con­ (0-9 m) covering 58-86 km2, 26-6% of the ditions, producing higher energy consump­ surface, a favourable characteristic for tion, the birds are forced to leaved the aquatic birds. wintering ground to seek others more The substratum of the littoral zone com­ favourable. The present study concerns the prises sand and mud (50-84 km2) and activities of Tufted Ducks Aythya fuligula gravel (8-02 km2). The gravel is concen­ wintering in Switzerland. trated in three deposit regions, Bas-lac, Most Swiss lakes were recently colonized Vaumarcus and Yvonand, which are the by Dreissena polymorpha, a bivalve mol­ main feeding and resting areas of the lusc which rapidly invaded the whole of the ducks, because of the high density of D. bottom of the littoral zone. This increase of polymorpha. biomass in the bentos attracted very high numbers of wintering Tufted Ducks. (Ped­ roli 1981a, b, c.) T h i e l l e Figure 1. Lake Neuchâtel—geographical sketch. 105 Wildfowl 33 (1982): 105-12 106 Jean-Carlo Pedroli Material and methods main feeding and resting grounds of Lake Neuchâtel was similar (Figure 2). Resting Field studies were conducted from 1975 to was the main activity everywhere. The 1979. The diurnal part of the time budget time devoted to preening was also similar was established in the winters 1976-1977 in each place. Diving, the feeding activity and 1977-1978 on the three main concen­ of the ducks, occurred only seldom. Dur­ tration points of Tufted Ducks on Lake ing daylight, there were two periods of Neuchâtel: Bas-lac, Vaumarcus and Yvo­ higher activity with swimming, and some­ nand. Every 15 to 30 minutes the indi­ times diving, in the morning when birds vidual behaviour of 100 birds, randomly had finished their nocturnal feeding and selected within a flock, was observed by late in the afternoon when birds initiate, telescope and recorded on a dictaphone, their feeding. Data collected from Lake according to the following categories: rest­ Geneva and the Niederried reservoir were ing, preening, swimming and diving (time also similar to those from Lake Neuchâtel. spent under water). The data were col­ lected throughout the winter under various meteorological conditions. The nocturnal Nocturnal activity part of the time budget was established during winter 1977-1978 in the same way, The results from both Lake Neuchâtel, using a night vision scope. Bas-lac, and Lake Geneva, Ouchy, were The electronic part was by RCA, USA; similar and contrast strongly with the diur­ amplification power 40,000x, catode S 20; nal pattern. During the night the birds the optic part by Zoomar, BRD, objective have their feeding activity, which at flock 180 mm, aperture 1:1-3. A minimum re­ level seemed to be constant throughout the sidual light was required, which limited our night. Between 30 and 50% of the time was investigation to the Bas-lac region, those of devoted to diving, the remaining time Vaumarcus and Yvonand being too dark. being spent swimming. Sometimes birds The observations were extended in preened, mostly in the first and last hours 1978-1979 to Ouchy on Lake Geneva, of the night and around midnight. today colonized by D. polymorpha, where As diurnal activity was the same in each day and night behaviour could be estab­ place of investigation, it is likely that night lished, and on Niederried reservoir, not yet activity was similar everywhere as well. colonized and for which only day activity This presumption was confirmed by the could be observed. number of ducks caught during the night in Our results are based on data from 1,259 gill nets used by commercial fishermen, groups of 100 birds: 856 diurnal and 106 1975-1976 to 1977-1978 at Ouchy, Bas-lac nocturnal on Lake Neuchâtel; 145 diurnal (306), Vaumarcus (78), and Yvonand and 66 nocturnal on Lake Geneva; and 106 (209). diurnal on Niederried reservoir. The time budget of a bird flock was expressed as a percentage of each activity. The activity rhythm During these instant observations of flocks every 15 to 30 minutes, flight pro­ Our results showed, without any doubt, an duced by sporadic disturbance was not alternation of diurnal resting and nocturnal considered. In several cases, however, con­ foraging activity. During daylight, resting tinuous observation for 232 hours allowed seemed to be very continuous, interrupted us to note the flight activity of the ducks, only briefly for individual birds by preen­ its causes and duration. ing. In a flock, this was randomly distri­ Bi-mensual ground or aerial counts of buted, not being induced by a collective the total wintering Tufted Duck population stimulus. In some rare cases, however, a of Lake Neuchâtel were conducted, to find whole bird flock began to preen, probably the number of bird-days for each concen­ when favourable conditions occurred, such tration place, and the fluctuation within as a rapid rise in temperature after the and between winters. disappearance of haze, or sudden sunshine on a cloudy day. Detailed observations of small bird Results groups during the night showed that diving was an irregular activity, stimulated by Diurnal activity collective behaviour. When an individual dived, other members of the group rapidly The activity of Tufted Duck on the three did the same, this sequence being repeated Tufted ducks on Swiss lakes 107 ac ti vi ty (#) 100 ^ 2 6 L. Neuchâtel, Bas-lac : : : : : 1976/1977 : : : : : : : : : : : : : : L. Neuchâtel, Yvonand'. : : : : : : 1976/1977 ::::::::::: 1978/1979 1— 1 i i i r i 1 i r rs 8 l o 12 14 16 h o u r s 100 [.. I Resting U H Preening £ 2 2 Swimming ¡¡¡¡¡¡piving Figure 2. Tufted Duck, daytime and night-time activity. at least ten times. The diving also stopped During the night, the ducks did not swim rapidly and the whole bird group began to from one place to another, but after a swim for several seconds. Again an indi­ series of dives, allowing them to regulate vidual began to dive and the whole group their respiration. During the day, only did the same, and so on throughout the isolated individuals in the flocks swam. night. This collective behaviour is probably Courtship activities were never observed. stimulated by the noise of a bird entering However, in some particular situations a the water. During these rapid diving sequ­ whole bird flock showed a high agitation ences the birds vocalized which also phase. All the ducks swam rapidly in the seemed to serve as a stimulation. same direction; some birds splashed, slap- 108 Jean-Carlo Pedroli ped their wings on the water and pursued Number o f bird-days on the three major others, uttering the same frequent vocal concentration points on Lake Neuchâtel noises as during feeding. These vocaliza­ tions were the only ones recorded. Agita­ Our data revealed (Table 2) that the num­ tion phases with rapid swimming were ber of bird-days on the Bas-lac region was observed on all the concentration points always higher than on the other two. and they always occurred at dawn and Annual fluctuations, however, were high. dusk. This can be interpreted as a sign of Yvonand and Vaumarcus had about the the transition between resting during the same number of bird days. day and feeding during the night. In some rare cases this behaviour was also observed in the daytime, especially after the disturb­ Disturbances producing flying ance of a flock or arrival on a new resting ground. For the Bas-lac region, where the ducks rest in a bird sanctuary, disturbances were minor (Table 3), in total duration as well as Duration o f the Tufted Ducks' activities in frequency. Their origin was, moreover, for the most part unconnected with man, For winter 1977-1978 on Lake Neuchâtel the wind playing a major role. The sanctu­ (Bas-lac), and 1978-1979 on Lake Geneva ary is situated at the north-eastern end of (Ouchy), the time devoted to the different the lake, where the south-west wind some­ activities was similar (Table 1). From the times produces high waves. Birds resting data collected for Lake Neuchâtel we were on open water away from the shore made able to divide the winter season into four periodic flights to adjust their position periods: when the wind and the waves pushed them 10.X-24.XI: lake with hunting pressure. near the shore. 25.XI-31.XII: lake with hunting and When ice covered the bird sanctuary, the fishing pressure. ducks sometimes rested on open water 1.1-31.1: lake with hunting pressure.
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