Group structures within a flock of Merino ewes and rams on a large paddock in semiarid pastoral country.

Abstract

GROUP STRUCTURES WITHIN A FLOCK OF MERINO EWES AND RAMS ON A LARGE PADDOCK IN SEMI-ARID PASTORAL COUNTRY I.C. FLETCHER* and A. NICOLSON+ Group structures within a flock of about 400 Merino ewes and rams on a 1550 ha paddock in semi-arid pastoral country were observed over a period of eight days. Small groups of ewes, often with a single ram, were seen around the paddock during the day, but they congregated at water in the early morning and/or evening into larger groups of ewes with several rams. The possible effects of this changing pattern of group structure on mating efficiency are briefly discussed. I. INTRODUCTION The group structures of sheep grazing on large paddocks in semi-arid areas of Australia have been described by Dudzinski, Pahl and Arnold (1969), Squires (1970), and Lynch (19721.. However, to quote Lynch (1973) s 'There is no information of the effects on groups of sexually active animals. Nor is there information about the possibilities of groups of ewes being isolated from rams'. General observation in the Gawler Ranges area of South Australia indicates that ewe flocks frequently split into small groups during th.e mating period. The present observations were made to determine whether grouping has any important effect on mating efficiency. II. MATERIALS AND METHODS Observations were made in a 1550 ha paddock on Middleback Station, about 22 km NW of Whyalla, South Australia. Vegetation is a woodland/shrubland complex in which myall (Acacia sowdenii], bluebush (Kochia sedifolia), and saltbush (Atriplex vesicaria) are the character plants. Abundant feed, which included Stipa spp. and Bassia spp., was available throughout the paddock during the period of observation. Woodland makes up more than 50% of the paddock area, and visual contact among much of this woodland is limited to a range of about 50 m. Stock water was available from a single dam sited on the southern boundary, About 400 &-year-old Collinsville strain Merino ewes were in the paddock with 14 Merino rams of mixed ages. Rams were put with the ewes on 2 January 19'75, and were branded on both mid-sides with numbers about 30 cm high so they could be individually identified, with the aid of binoculars, from a distance of up to 100 m. # + Agricultural College, Roseworthy, S.A. 5371 Middleback Station, via Whyalla,-'S.A. 5600 145 Ten sets of observations of the ewes and rams were made over a period of eight days between 8 and 15 January 1975. Five of these were made early in the morning (between about 0600 and 0800h), three during the day ([between about 1000 and 1400h), and two in the evening (between about 1800 and 2000h). Each time, observations were first made at the dam to record the nmbers of sheep at water. Further observations were made through an area within about 1 km radius of the dam in the mornings, and through an area within about 3 km radius of the dam during the days. No sheep had been found further than about 3 km from water during preliminary surveys. Observations were made by moving through the paddock on foot, since previous experience had shown that the use of vehicles caused small groups of sheep to flock together. Records were taken of all groups of sheep sighted, their approximate position in the paddock and any obvious direction of movement, and the number and identity of rams in the groups. Groups of up to 15 sheep were counted accurately, but larger numbers were recorded only as estimated classes of about 20, 30, 50, loo,, 150, or 200 sheep. Animals judged to be beyond visual contact in wooded areas, or greater than 100 m apart in open country, were classed as belonging to separate groups. III. RESULTS Observations of sheep groups were limited for two reasons. %irst, sheep began moving away from the dam before sunrise, so only those remaining when it was light enough to distinguish ram identities were recorded. Second, some groups remained undetected during each period of observation because the undulating and heavily-wooded nature of the paddock, and the necessity to make observations on foot, make complete visual coverage of the paddock impossible. On average, eight rams and about 150 ewes were seen during each period of observation. Sightings of groups of sheep, classed according to the number of rams present and'their position in the paddock, are shown with approximate group sizes in Table 1. TABLE1 Sightings of groups of sheep according to location in the paddock and the number of rams present (pooled results from 10 observations spread over 8 days). Figures in parentheses are estimates of the mean numbers of sheep per group 146 Mean group sizes are based on estimates, and are not amenable to statistical analysis. They nevertheless indicate that group size was greatest at the dam and least away from the dam, and that group size was positively associated with the number of rams present. Significantly more multiple ram groups were seen at or movsng away from water than were seen away from or moving in to the dam (x = 24.7, d.f. = 1, P(O.001). Thus groups tended to comprise large numbers of ewes with several rams at the dam, and small nwnbers of ewes with a single ram away from the dam. Nine groups (17% of all groups sighted, but only about 4% of all animals sighted) seen away from the dam did not include a ram. On average, nine rams were seen at or near the dam each day. On the one day when observations were made at the dam in both the morning and the evening, four rams were seen only in the morning, two only in the evening, five in both the morning and the evening, and three not at all. More than 200 ewes were seen at water in the morning, and about 150 in the evening. These limited data indicate that most rams and ewes were coming in to water at least once per day, though not necessarily at the same time of day. IV. DISCUSSION These observations clearly confirmed local opinion that ewe flocks split into small groups during the mating period. This contrasts with observations of Squires (1970) and Lynch (1972) that sheep on large paddocks with abundant feed remained in a single flock or split into few large groups. The sexually active flock and heavily-wooded paddock used in this study, compared with the sexually inactive flocks and sparsely-wooded paddocks studied by other authors, may account for the difference. Dudzinski, Pahl and Arnold (1969) and Lynch (1972) have observed sheep scattered throughout large paddocks in small groups, but only during periods of food scarcity. Any effect of grouping on mating efficiency would depend on whether the composition of small groups was static or dynamic, and group structure in the present study obviously did not remain constant. Small groups of ewes, frequently with a single ram, were seen away from water during the day, but they congregated-at the dam into larger groups of ewes with several rams in the early morning and/or evening. Active partner-seeking behaviour shown by rams (Lindsay 1965) and ewes in oestrus (Inkster 1957) should ensure sexual contact among animals at the dam. Groups of ewes seen without rams might remain isolated if they watered *hen there were no rams at the dam, since the partnerseeking activity of ewes in oestrus may only occur when rams are within the range of visual contact (Lindsay and Fletcher 1972). Prolonged isolation of this nature seems unlikely however, since many sheep appeared to water at least once per day, and ewes were never seen at the dam without rams also being present. Even if prolonged isolation occurred, the relatively small numbers of ewes seen isolated from rams (about 4% of all sh eep sighted in this study) would not constitute a major problem of reduced mating efficiency on a whole flock basis. 147 Contact between ewes and rams might be inhibited if sheep remained away from water for extended periods (as observed by Lynch 19721, and remained scattered throughout the paddock in small groups such that some ewes were beyond the range of visual contact with rams. Under the conditions of the present study, however, it is concluded that the separation of ewe flocks into small groups during the mating perioddid not seriously affect ewe-ram contact and successful mating. V. REFERENCES Journal of DUDZINSKI, M.L., PAHL, P.J., and ARNOLD, G.W. (-1g6g1, Range Management, 22: 230. INK&R, I.J. (1957). New Zealand Sheep Farming Annual, p.163. LINDSAY, D.R. (1965). Animal Behaviour, 13: 75. LINDSAY, D.R., and FLETCHER, I.C. (1972). -Animal Behaviour, C 452. 20: LYNCH, J.J. (1972). Proceedings of Conference on Behaviour of Ungulates and its Relations to Management, ed. V. Geist and (International Union for Conservation of Nature: F. Walther. Switzerland.) LYNCH, J.J. (1973). Proceedings of Symposium on Studies of the Australian Arid Zone. 2. Animal Production, ed. A.D. Wilson. (CSIRO: Melbourne). SQUIRES, V.R. (1970). M.A. Thesis, University of New England. 148