Egg-turning rates in birds: A review of recording methods and the influence of egg composition and developmental maturity

Abstract Egg turning during incubation is a crucial behavior in birds that influences embryonic development, yet its underlying evolutionary drivers remain poorly understood. Recent advances in technology, particularly the integration of triaxial accelerometers and magnetometers, have significantly improved the accuracy of egg-turning measurements in nests. This study reviews the methods for determining egg-turning rates and examines how egg-turning rates are influenced by egg mass, egg composition, female body mass, incubation period, and developmental maturity of hatchlings. Data were compiled from published sources together with new unpublished findings. The results showed significant variation in turning frequency across bird orders and developmental maturity groups, with the highest rates observed in altricial species and the lowest in super-precocial megapodes. Phylogenetically controlled regression analysis revealed that a significant negative relationship between turning frequency and incubation period was the best model, although other variables also exhibited highly significant relationships. This study highlights the complexity of avian incubation strategies and the need for further research to better understand how egg turning affects embryonic development across species.