Abstract:
FOX PREDATION AS A CAUSE OF LAMB MORTALITY R. W. MOORE*, I. M. DONALD and J. J. MESSENGER* Summary Neo-natal lamb mortality was investigated in a flock of 545 Merino ewes under two management systems during lambing at Minnipa, South Australia. Lamb mortalities of 21 and 27% in the drifted and set stocked groups respectively were not significantly different. Both primary predation (P < 0.05) and mutilation of lamb carcases (P < 0.001) were higher in the set stocked group. The fox was responsible for most deaths due to primary predation; of four foxes killed, the stomachs of three contained fresh lamb carcase. Proximity to native scrub and the system of management are suggested as contributing factors to the higher predation-mutilation pattern in the set stocked group. I. INTRODUCTION Predation as a cause of lamb mortality has been considered of minor importance by Alexander, McCance and Watson (1955), McFarlane (1964), Hughes et al. (1964) and Dennis (1965), although Moule (1954) and Smith (1964, 1965a, 1965b) found high levels of predation in Queensland. McHugh and Edwards (1958) and Davies (1964) measured lamb deaths associated with predation. Individual flocks have sometimes suffered heavy predation losses (Moule 1954) due to a killer or rogue fox (McIntosh 1963; McFarlane 1964). In this paper, evidence is presented that fox attack contributed to, neo-natal lamb mortality and that in two commercial management systems of lambing under study, its effect was less in the drifted than in the set stocked group. II. MATERIALS AND METHODS The observations were carried out on a flock of 545 Merino ewes aged two to six years at the Minnipa Research Centre, situated in a wheat-sheep area of South Australia receiving a 13 in. (33 cm) rainfall. On April 7, 1965 the flock was divided into two groups of almost equal numbers, previously matched for age and body weight. One group was drifted and the other group set stocked during lambing which extended from April 11 to May 24, 1965. A 136-acre paddock of windrowed hay and unreaped oats was subdivided into two. The drifted group area was further divided into three drifting paddocks of approximately eight acres each (Dl, D2 and D3), (Figure 1) and a 42-acre 'bulk up ' area (BU) (Figure 1). Unlambed ewes were separated at dawn each day. Ewes with lambs remained in the drifting paddocks for 48 to 72 hours after birth and were then shifted into the bulk up paddock. All sheep were inspected and lamb carcases collected at dawn and 4 p.m. Lamb mortalities were classified according to D. M. Keenan (personal communication). *South Australian Department of Agriculture, Adelaide, S.A. $South Aust ra 1ran Department of Agriculture, Research Centre, Minnipa, S.A. ' $Present address: Department of Animal Science, Purdue University, Lafayette, Indiana, U.S.A. Fig. l.-Location and subdivision of a 136-acre paddock used in the lambing observations. KEY S-set stocked group. D 1, D2, D3-drifting paddocks. BU-bulk up area for drifted group. a-2500 ac paddock of adjoining property. b-pine and mallee scrub for one mile. c-four feet high netting fence from point c southwards. d-scrub with stone and stump heaps. h-hay, windrowed. o-oats, unreaped. Predation was defined as lambs showing injury with haemorrhage, indicating that the lamb was alive when injured; (a) primary predation: an apparently normal lamb showing signs of fatal injury as the only abnormality, or (b) secondary predation: a weak lamb that walked but did not suck, usually with fat reserves metabolised. A stocked the set between 0.05). III. RESULTS AND DISCUSSI0N total of 633 lambs was born, 320 in the drifted group, 3 13 in the set group. In the drifted group, there were 21% mortalities (67 lambs) ; in stocked group there were 27% mortalities (85 lambs). The difference the numbers of mortalities in the two groups was not significant (P > TABLE 1 Classification of lamb mortailities :sThese carcases were found outside the Drifted and Set-stocked areas. A classification of 157 carcases collected from the two groups showed (Table 1) that the only significant difference between the two treatment groups was in the level of primary predation (P' < 0.05). Mortalities due to primary predation were 12.1% of lamb deaths and 19/633 or 3.0% of lambs born. All predation (Classes 7a and 7b) accounted for 26.7% of lamb mortalities or 6.6% of lambs born. These figures are similar to those found in a survey by McFarlane ( 1964). Table 2 shows a dissection of total carcases on a basis of mutilation. Mutilation includes damage to lambs before and after death. The types of mutilations attributed to foxes were: crushed skulls, removal of jaws, heads, or heads and necks, and bitten throats with little attempt made to eat the carcase. Of the 19 primary predation deaths, seven showed these types of mutilation with no other carcase damage, and ten showed additional body, leg and tail mutilation most certainly due to foxes. TABLE 2 Mutilations of carcases 159' Eleven foxes were sighted and shot in and around the lambing paddocks on the night of May 4, 1965 and of four fox carcases recovered, the stomachs of three contained fresh lamb identified by its wool, and the fourth contained sheep carrion. The set stocked group suffered both a higher level of primary predation (P < 0.05) due almost entirely to foxes, and more mutilation of carcases (P < 0.001) than did the drifted group. Two explanations are suggested for this predation-mutilation pattern: ( a 1 Proximiiy to native scrub may have offered good cover for foxes. Scrub was close to both the set stocked area and paddock D3 which incurred the heaviest predation and mutilation in the drifted group. A four feet (1.3 m) high dog fence extending southwards beyond the lambing area indirectly protected the bulk up paddock of the drifted group. W The drifting system created small groups of ewes with lambs of similar age in small paddocks, a situation which could allow the formation of strong bonds between ewe and lamb (Alexander 1960). The set stocked group of 274 ewes in one group with lambs of all ages may have given greater scope for separation of lamb from ewe with consequently greater exposure to attack by predators. IV. ACKNOWLEDGMENTS We would like to thank Mr. C. J. Mulhearn for much helpful encouragement, advice and criticism of the manuscript. Grateful acknowledgment for financial assistance is made to the Wool Research Trust Fund. V. REFERENCES A A D G. ( 1960). Maternal behaviour in the Merino ewe. Proceedings of the Australian Society of Animal Production 3: 105. LEXANDER , G., MCCANCE, I., and W ATSON , R. H. (1955). Some observations on losses among Merino Lambs. 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