Sheltering behaviour of lambing Merino sheep in relation to grass hedges and artificial windbreaks

Abstract

This study extends previous findings that recently shorn, lambing ewes made extensive use of the shelter provided by hedges of a tall grass (Phalaris hybrid) and that the provision of such windbreaks was associated with a reduction in lamb mortality. The study compares phalaris hedges with fences of a polyethylene garden-mesh (Sarlon; 60% porosity) and examines the effect of different spacings between Sarlon shelters. The phalaris reduced wind speed over the lee 20 m to a greater extent than Sarlon. In contrast to the marked concentration of ewes immediately adjacent to the lee of the phalaris (0–2 m), ewes were dispersed over a greater distance (0-6 m) from the lee of the Sarlon; at night about 12% more of the flock were found within 6 m of the lee of the phalaris than within the same distance of the Sarlon. In addition to the proportion of shorn ewes that were expected to be in shelter on the basis of random distribution alone, c. 35% were found within 6 m of the shelter at night, and 15% during the day regardless of whether Sarlon shelters were 20, 40 or 80 m apart. Unshorn ewes made very little use of the shelters, and lambs from shorn and unshorn ewes made more use of shelters and particularly of the phalaris than their mothers. Ewes tended to congregate at one end of the paddock regardless of wind direction and the presence of shelter, which indicated a role for strategic selection of sites for shelters. As in the previous study, lamb mortality was lower in the sheltered than in the unsheltered group, especially amongst twins.