Simple SummaryIn some species of birds, asynchronous hatching occurs when incubation begins before completion of clutch, resulting in age differences between nestlings. According to the brood reduction hypothesis, which explains the reason for asynchronous hatching, selective survival is permitted only for older nestlings when availability of food is unpredictable. Due to the feature of food distribution, passerines are not likely to practice selective feeding of older nestlings. The essential purpose of this study is to determine whether the brood reduction hypothesis can explain asynchronous hatching in passerines. Infrared cameras were installed inside nest boxes to determine whether great tit (Parus major) parents, which show asynchronous hatching, practices selective feeding of older nestlings. The results of this study showed that great tit parents did not practice selective feeding of older nestlings, highlighting that using the brood reduction hypothesis to explain asynchronous hatching of great tits is not reasonable. Further research is needed in order to explain the adaptiveness of asynchronous hatching.AbstractThe brood reduction hypothesis, which explains asynchronous hatching in birds, as an adaptation that enables selective survival of older nestlings when availability of food is unpredictable. This study was conducted in order to determine whether the brood reduction hypothesis can explain asynchronous hatching in passerines. Infrared cameras were installed inside nest boxes where great tits (Parus major) were attempting to reproduce in order to determine whether the parents practiced selective feeding of older nestlings. According to the results of the study, no significant difference was observed between the hatching order and the average number of feedings per nestling. In addition, when examining the distribution of food according to hatching order over time, every 30 min, beginning at 9 a.m., selective distribution of food to older nestlings was not observed. In conclusion, use of the brood reduction hypothesis, which supports selective provision of beneficial feeding of older and larger nestlings, to explain the asynchronous hatching of passerines is problematic, thus conduct of future studies focusing on other hypotheses in order to explain the asynchronous hatching of this passerine bird will be necessary.