Fox predation as a cause of lamb mortality on hill farms.

Data collected between 1993 and 1996 from two Scottish hill farms were used to assess the potential importance of predation by foxes as a cause of lamb mortality. Farm 1 was in Midlothian and farm 2 in West Perthshire. Overall lamb mortality rates from birth onwards were 10.2 per cent for farm 1 and 9.3 per cent for farm 2. Sixteen lambs were identified as killed by foxes on the two farms during the four-year period. The minimum rates of fox predation were 0.6 per cent for farm 1 and 0.2 per cent for farm 2. All confirmed cases of fox predation were recorded during the period until the lambs were marked at about six weeks of age, and during this period another 53 lambs went missing from the two farms. Both groups of missing lambs were characterised by having significantly more siblings than the remaining lambs. A logistic regression model was able to classify the lambs killed by foxes and the missing lambs with 75 per cent accuracy on the basis of their birth rank alone. Of the total potential revenue from lamb production, the maximum losses due to confirmed fox predation in any one year were equivalent to 1.5 per cent on farm 1 and 0.6 per cent on farm 2.