Ptilochronology: Feather Growth Bars as Indicators of Nutritional Status

AsSTRACT.--Ptilochronology is the study of the growth rates of feathers by the measuring of growth bars.Growth bars are cross-bands on feathers that denote 24-h periods of growth.If a rectrix is plucked from a bird that is released, and then recaptured more than a month later, the width of the growth bars on the replacement (or induced) rectrix can provide a day-by-day record of the nutritional regime under which the bird had lived.Growth rate of induced rectrices varies among ages, sexes, and species of birds.I measured growth bars on feathers induced in Downy Woodpeckers (Picoides pubescens) that wintered in Ohio woodlots without supplemental food.On a daily basis, females grew feathers significantly more slowly than males.In other woodlots, where the woodpeckers were given supplementary food, daily feather growth did not differ between sexes.I concluded that male Downy Woodpeckers normally have a better nutritional status than females during the winter.A difference in nutritional status may explain why male Downy Woodpeckers use their social dominance to exclude females from parts of the species niche during winter.Ptilochronology could permit new insights into the nutritional ecology of free-ranging birds.Hypotheses that predict even minor variation in the nutritional status of birds should become accessible to testing.