Use of shelter and selection of lambing sites by shorn and unshorn ewes in paddocks with closely or widely spaced shelters

Abstract

This paper extends previous findings that recently shorn ewes make extensive use of the shelter provided by grass hedges, of a phalaris hybrid, 20 m apart, whereas unshorn ewes make no use of the available shelter. In the present study, shorn sheep were observed sheltering near phalaris hedges, 240 m apart, for about 30% of the time during the day and 60% of the time during the night, compared with 60% and 80%, respectively, for shelters 20 m apart. These differences can only partly be accounted for on the basis of chance occupancy of shelter, since 10% fewer sheep appeared to move to shelter with the spacing of 240 m than with a spacing of 20 m. Shelters were also used extensively by shorn ewes during periods of inclement weather during the day. Lambs made slightly more use of shelter than their mothers. The use made of shelters in the form of fences of black, plastic mesh (60% porosity), 240 m apart, was only 70% of the use made of similarly spaced phalaris hedges. Ewes, with the exception of unshorn ewes that were still to lamb, spent a disproportionately large amount of the time at the eastern or up-hill end of the paddocks. During the day, the proportion of shorn ewes lambing in the lee of the widely spaced shelters was similar to the proportion of ewes in shelter (about 30%), but during the night when 50–70% of the ewes were in shelter, the proportion of lambing sites in shelter was well below this range. In contrast, while only 10–20% of unshorn ewes lambed near the widely spaced shelters, this was several fold higher than the small proportion of non-lambing unshorn ewes in shelter. In addition, of the shorn and unshorn sheep that lambed away from shelter in these paddocks, some 50% more than expected on the basis of even distribution lambed in close proximity to the boundary fences; this disproportionate distribution was not seen in ewes that had not lambed. These results indicate that perhaps half of these Merino ewes isolated themselves from high concentrations of other sheep, for lambing, and in the process lambed near boundary fences or shelters. It is not clear whether the movement to isolated lambing sites is deliberate or fortuitous due to restlessness arising from physical discomfort. Lambing sites of both shorn and unshorn ewes were more concentrated near the eastern or up-hill end of the paddocks than the positions of ewes that had not lambed; the eastern end was clearly a preferred lambing area. The provision of ample shelter near any preferred lambing areas in large paddocks could lead to many lambs being born in shelter and hence to a reduction in mortality of lambs born during inclement weather.