Choice of foraging patches by hill sheep given different opportunities to seek shelter and food

Abstract

AbstractA patch choice experiment was conducted in which sheep were offered choices between patches of upland pasture which differed in their sward height and degree of shelter from the wind. Experimental plots (48 m ✕ 4 m) were divided into 4 m ✕ 4 m patches. Alternate patches were mown in advance of the experiment to create nominal sward heights of 4 and 6 cm. Portable shelters were erected on the windward side of alternate patches to reduce wind speed on sheltered patches by half. The four treatment combinations used to test the influence of sward height, shelter and their interaction on patch use were: patchy swards with and without shelters and uniform swards with and without shelters. Five adult sheep per treatment were observed while grazing the plots for 6 h/day on five occasions (days) in autumn. Patch choice was measured by video observation and using a patch marker technique. On none of the observation days was the weather condition sufficiently severe that animals were outside their thermoneutral zone. There was a strong influence of sward height on patch use with sheep spending 0·382 of their time on short swards when patchy swards were offered compared with 0·503 of their time on equivalent areas when swards were uniform. Thermal conditions did not influence patch choice with sheep spending an average of 0·442 of their time on equivalent patches whether they were sheltered or not. There was no interaction between sward conditions and thermal conditions on the amount of time spent on different patches. Data from the patch marker method supported observation data. The results confirm that sheep are resilient to extremes of cold weather commonly occurring at temperate latitudes and suggest that thermal constraints have minimal influence on the small-scale foraging movements of sheep, as long as they remain within their thermoneutral zone.