Figure 2.

Seasonal variation in onset, end and length of subjective day. We retrieved data from birds tagged and recaptured in three different habitats (rural forest, circles; urban park, triangles; and business district, squares), between the end of March and the end of June, from a total of 32 birds (see figure 1 for sample sizes). Each symbol represents the mean for an individual bird, and all means are standardized to the relative sunrise (a), sunset (b) and total number of daylength hours (c). We found a significant effect of date on the onset of the subjective day (a) and the subjective daylength (c), such that early during the breeding season the onset of day was earlier and the subjective daylength longer in urban birds compared with the forest conspecifics. No significant effect of date was detected for the end of the subjective day (b). Trend lines represents data simulated from the model using the function predict in the R package lme4 [26] (dashed line, rural forest; solid black line, urban park; solid grey line, business district). Date was plotted as the midpoint between the two capture dates for each individual.