Fig. 1

Exemplification curve representing the cumulative proportion of encounters in a cell for (a) bird species that do not winter in the study area; (b) bird species in cells where few birds winter; (c) bird species in cells where many birds winter. In b) the onset of the non-stationary period is estimated as the date when the curve deviates from an approximately linear growth in the left tail. In c) the onset of migration is estimated by a decrease, rather than an increase, in the proportion of encounters