<p>Contour plots of the date in which the CAR model predicts that a given percentage of Barn Swallows have been recorded during (A) spring and (B) autumn migration. Contours were generated by linear kriging interpolation. Numbers in the colour scale represent the mean date for each 10-days colour belt (1 January = 1). For ease of interpretation we here report some reference dates: 100 = 31 March, 120 = 30 April; 150 = 30 May, 180 = 29 June, 200 = 19 July, 230 = 18 August, 260 = 17 September, 300 = 27 October.</p
