Can home range be used as an identifier of lambing for grazing pregnant Merino ewes?
R.C. DobosA,D, D.B. TaylorB,D, M.G. Trotter,C,D and G.N. HinchB,D
AN.S.W.
Department of Primary Industries Beef Industry Centre of Excellence, Armidale, N.S.W., 2351
of Environmental & Rural Sciences, University of New England, Armidale, N.S.W., 2351
CSchool of Science & Technology, University of New England, Armidale, N.S.W., 2351
DPrecision Agriculture Research Group, University of New England, Armidale, N.S.W., 2351
BSchool
Lamb survival is a critical issue within sheep flocks (Alexander 1986). Therefore, understanding grazing
pregnant ewe behaviour before, during and after lambing could help reduce lamb losses. Devices such as global
positioning systems (GPS) have the potential to remotely monitor behavioural indicators that could be used to
identify the onset of lambing. Such indicators could then be used to help improve lamb survival. Taylor et al.
(2011) reported how GPS tracking devices helped in understanding grazing pregnant Merino ewes’ use of shelter
at lambing. An alternative behavioural indicator that could be used is the animal’s home range as its size,
location and shape may change depending on the physiological state of the individual and environmental
conditions. Many of the statistical methodologies to estimate home range have their origin within wildlife and
endangered species research. It is unknown if these statistical methods would be suitable to identify changes in
ewe behaviour within small paddock sizes.
GPS locations from 5 single bearing Merino ewes with known lambing dates (Taylor et al 2011) were used
to determine if lambing influenced home range size. Paddock size was 20ha. To calculate home range, a 90%
minimum convex polygon (MCP, Mohr 1947) was used for each ewe 7d before, at lambing, and 3 and 7d after
lambing.
There was a significant (P=0.02) reduction in mean 90% MCP size at lambing, while it increased after
lambing. Home range varied considerably between individual ewes before and after lambing but was less
variable at lambing (Table 1).
Table 1. Mean (± se) and individual 90% MCP home range (ha) for grazing pregnant Merino ewes 7d
before lambing, at lambing, and 3 and 7d after lambing.
Period
Mean (± se) 90%
MCP area (ha)
Individual ewe 90% MCP area (ha)
Ewe number
1
2
3
4
5
7d before lambing
7.7 (± 1.63)
7.1
4.4
10.8
4.1
12.1
Lambing
3.5 (± 0.72)
5.3
3.1
1.6
5.0
2.4
3d after lambing
6.9 (± 1.60)
5.5
2.3
6.5
11.8
4.1
7d after lambing
9.9 (± 0.74)
8.6
8.4
9.5
12.3
10.8
Grazing pregnant Merino ewe home range size is reduced at lambing. Therefore, size of home range could
possibly be used by the producer to identify the onset of lambing and implement strategies to potentially reduce
lambing losses. A major limitation to this research was that only 5 ewes were fitted with GPS collars. Therefore,
this could limit the usefulness of home range as a metric to identifying lambing. The MCP technique is subject to
bias, and further analysis should utilise methodologies that reduce bias in estimating ewe home range. Therefore,
estimations of home range using other methods is warranted to further test the validity of this concept to
determine its suitability as an identifier of changes in ewe behaviour because of lambing.
Alexander G. (1986) In “Factors affecting the survival of newborn lambs”, (Eds G Alexander, JD Barker, J Slee)
p. 99 (Commission of European Communities: Luxembourg).
Mohr C.O. (1947) The American Midland Naturalist 37, 223.
Taylor D.B., Schneider D.A., Brown W.Y., Price I.R., Trotter M.G., Lamb D.W. and Hinch G.N. (2011) Animal
Production Science 51, 724.
Email: robin.dobos@dpi.nsw.gov.au