Figure 1.

Relationship between the best individual environmental predictor variables and two measures of blue tit reproductive phenology (a–c: nest initiation, d–f: lay date). (a) Mean night-time (2000–0500 h) temperature during the period 24 February–18 April; (b) mean birch budburst date; (c) mean invertebrate availability during the period 23 March–5 April; (d) mean night-time (2100–0400 h) temperature during the period 16 March–8 May; (e) mean birch budburst date; and (f) mean invertebrate availability during the period 3 April–3 May. All slopes shown are taken from the best predicting models summarized in the electronic supplementary material, tables A2–A4 and significant slopes are marked with an asterisk.