Discrimination of colours and grey shades by Merino ewes: Tests using coloured lambs

Abstract

The tendency of lactating ewes to run to lambs visible some distance away, was used to examine the responsiveness of ewes to various colours and to test the ewes for colour vision. Lambs were coloured red, orange, yellow, green or blue (colour series) and white, black or one of eight shades of grey (grey series) by dusting pigments or mixtures of talc and carbon black into the coat. Ewes presented with their own lamb immediately after colouring showed various types of abnormal behaviour, the incidence of which clearly increased with increased darkness of grey. In the colour series there were few abnormal responses to yellow, more to orange and a high incidence with green, blue and red. Thus red is either seen as a dark colour or has a special visual impact. Tests on colour vision were carried out 3–4 days later when ewes had become accustomed to the colour of their lambs. In these tests, ewes and lambs were separated for several hours, and “multiple choice” tests were then conducted using 4 or 5 alien lambs each in a separate wire-mesh cage; one of the lambs was the same colour as the ewe's own lamb while the others were from the grey series. The ewe was released 7 m from the cages, and her choice of cage was assessed by several criteria. Two consecutive tests were done so that each ewe was offered a choice between own colour and most of the grey shades. The ewes showed a significant preference for own colour when this was red, orange, yellow and white, but ewes whose lambs were blue, green, a light grey, a darker grey or black performed poorly. These results indicate that ewes have some sort of spectral vision, at least for colours in the longer wavelength range.