Selection of heather by captive red grouse in relation to the age of the plant.
A method for measuring food preference of captive red grouse (Lagopus lagopus scoticus) is described. Selection from heather (Calluna vulgaris) of different ages was studied for 2 years and some samples were analysed chemically. The grouse showed a marked but unexplained distaste for 1- and 2-year-old heather. This provides a possible explanation for the delay in the increase in grouse numbers after heather burning. Grouse often preferred 3- and 4-year-old heather and this corresponds with greater contents of N and P than in older heather. When captive birds were growing or laying, preferences were correlated with the N and P contents of the heather, but less of the youngest heather was eaten than expected on this basis. It is suggested that preferences were conditioned by physiological state of the birds. The proportion of Erica cinerea taken followed the same pattern in captivity as in the wild, decreasing from summer to winter and increasing again in spring. The amount of E. tetralix eaten also decreased from summer to winter, but did not increase in the spring as it does in the wild.