UC Davis

Growth rates of American barn owl (Tyto furcata) nestlings in the Central Valley of California were examined for this study. Growth rates between male and female fledged nestlings were compared and growth patterns were found to be similar between sexes. The data best fit growth models that were split between Gompertz and logistic depending on the parameter and sex of the given model. Morphometrics correlated with reversed sexual dimorphism which has been reported for other barn owls. Measurements between fledged nestlings and adults were also compared and fledging measurements of hallux, culmen, and body mass had not reached adult sizes according to Welch’s t-test. The results from this study suggest that American barn owl nestlings continue to grow post-fledging. Female and male nestlings have wing and tail lengths that are longer than adult averages, respectively, which is seen in other hatch year bird of prey species. To our knowledge, this is the largest published dataset of the American barn owls’ growth patterns. With barn owls being used in integrated pest management strategies throughout California, this information may help future research using barn owls in these systems to identify natural and artificial environmental impacts on their growth.