Species and housing
Between July and September 2018 we established 45 pairs of zebra finches from a pool of wild-derived captive birds available at Macquarie University. Randomly chosen groups of three males and three females were placed in aviaries 230×175×410 cm (height ×width ×depth), containing four nest boxes (22×12×15cm) located 175cm from the ground and shaded from direct sunlight. Birds were fed dry finch seed mix and waterad libitum , with a daily supplement of hardboiled eggs, cuttlebone and green seeds. After an initial week of acclimation, birds were provided with November grass, cotton strings and Emu feathers to allow nest construction. Clutches were monitored occasionally during the first part of the incubation and checked multiple times a day when approaching hatch date. When exact hatching date was ascertained, we experimentally heated 13 nests with a minimum brood size of three and simulated the same experimental procedure for 12 control nests (See Tables S1-4 for a detailed description of the sampling protocol). Our set up allowed us to control for food availability (Hall et al.2004) and prevented all sources of predation risk (Noguera & Velando 2019) that are also factors known to have reflections on telomere dynamics.