Fig. 4. Association between metabolic rates (measured at ±20.8°C) of starlings measured during the day (MR_day) and the night (MR_night) during a 24 h respirometer measurement. MR_day and MR_night were strongly correlated (r=0.75, N=24, P<0.001, controlling for mass); the regression line is shown. The grey lines show the average values of MR_night for our birds and the estimated values of MR_day in the rich and poor environment.