Figure 1
From: Barn swallows long-distance migration occurs between significantly temperature-correlated areas
Continental scale analysis of correlations between temperatures at departure of barn swallows from Africa and at their arrival in Europe. (A) Ranking of partial correlations coefficients between temperatures at departure time from Africa (τA,t, see text) and at arrival time in Europe (τE,t). Climatic series in the actual African locations are contrasted to alternative locations in the whole sub-Saharan African subcontinent (see broad scale simulation test in Methods). The dashed line is the expected distribution if no site selection occurred (complete random process). (B) Geographical locations of the 61 barn swallows for which τA,t explained at least 10% of the variance of τE,t. Circles identify individuals that winter either north of 7°S (cluster N) while dots those that winter south of 18°S (cluster S). Colors code the sign of the partial correlation coefficient between τA,t and τE,t (red for positive and blue for negative partial correlation). Dot size is proportional to the number of individuals found at any location. (C) Scatterplot of temperature anomalies in breeding vs wintering areas for individuals of cluster N whose migratory relevant temperature conditions in Africa explain more than 10% of variance of their European equivalent. Data referring to the same individual are denoted by a unique color: each circle represents the values of wintering and breeding temperatures anomalies for the focal individual in one of the 30-years of climatic reference for it. (D) As (C), but for cluster S.
