Fig. 3. The effect of multiple step changes in the magnetic field and time of season on migratory fuelling in thrush nightingales. Data from experiments in 2000 and 2001 are pooled. Body mass increase from day 1 (mean ± s.e.m.) for the early (A) and late (B) replicate, respectively. Experimental birds receiving a magnetic treatment are represented by open symbols; control birds are represented by filled symbols. In the early replicate, experimental birds increased more in body mass than control birds, whereas in the late replicate there was no difference between the treatments (ANOVA with repeated measurement; early replicate: F_1,12=8.1, P=0.02; late replicate: F_1,12=0.1, P=0.8). From Kullberg et al. (Kullberg et al., 2003).