LAUSR

20 Reproduction is costly. Despite this, evidence suggests that parents sometimes feed unrelated 21 offspring. Several hypotheses could explain this puzzling phenomenon. Adults could feed 22 unrelated offspring that are (1) of their close social associates to facilitate these juveniles’ 23 integration into their social network (the social inheritance hypothesis), (2) potential extra24 pair offspring, (3) at a similar developmental stage as their own, (4) coercing feeding by 25 begging, or (5) less-developed (to enhance their survival, which could benefit the adult or its 26 offspring; the group augmentation hypothesis). Colonial breeders are ideal for investigating 27 the relative importance of these hypotheses because offspring are often kept in crèches where 28 adults can exhibit allofeeding. Using automated monitoring of replicated captive zebra finch 29 (Taeniopygia guttata) colonies, we found that while parents selectively fed their own 30 offspring, they also consistently fed unrelated offspring (32.48% of feeding events). Social 31 relationships among adults prior to breeding did not predict allofeeding, nor was allofeeding 32 directed towards potential genetic offspring. Instead, adults with more-developed offspring 33 preferentially fed less-developed non-offspring over non-offspring at a similar developmental 34 stage as their own offspring, and this tendency was not explained by differences in begging 35 behaviour. Our study suggests that allofeeding is consistent with group augmentation, 36 potentially benefiting adults through colony maintenance or increased offspring survival. 37 38