During his PhD, Nicolas Dubos worked at distinguishing the direct effects of temperature on juvenile body size from the indirect effets of temperature via primary production, in temperate common songbirds (41 species from all over France, with the French Constant ringing Effort Site dataset). It resulted that spring primary production (indexed by NDVI) is a better predictor of body size (positive effect) than spring temperature. To know more, please, read the paper:

Dubos, N., Le Viol, I., Robert, A., Téplitsky, C., Ghislain, M., Dehorter, O., Julliard, R. and P.-Y. Henry (2018). Disentangling the effects of spring anomalies in climate and net primary production on body size of temperate songbirds. Ecography (Cop.)., 41, 1319–1330