Figure 1.

Breeding unit size effects. (a) Increasing breeding unit size was associated with an asymptotic increase in annual fledgling productivity (see electronic supplementary material, table S1a: y = 4.63–6.77x⁻¹; n = 125 measures, 106 breeding females, 3 years); and (b) Manipulating unit : brood size ratio led to a similar asymptotic relationship on the per capita rate at which nestlings received food (see electronic supplementary material, table S1b: y = 14.36–12.55x⁻¹; n = 15 measures (one data point is missing due to equipment failure), eight nests). Points show (a) raw means (±s.e.) and (b) raw values for each nest-treatment combination. Lines are generated from the best models. Brackets show naturally occurring range of unit : brood size ratios for the given range of unit sizes.