Physiological responses to social treatment: (a) body condition (SMI), (b) heterophil-to-lymphocyte ratio (H/L ratio, an indicator of physiological stress response), (c) oxidative damage to lipids (i.e. malondialdehyde, MDA), and (d–e) constitutive immune capacity, as expressed through agglutination score (d) and lysis score (e). Model-predicted mean ± s.e. are shown for each treatment group both at pre-treatment (dark bars) and post-treatment (light bars) sampling events. (f) Male house sparrow painting credit: Márton Zsoldos. (Online version in colour.)