We investigated whether the badge size of the Eurasian Tree Sparrow Passer montanus is correlated with morphological traits and hematocrit during the breeding season in order to elucidate the function of badge size as a potential signal of body size and physiological condition. We found a positive correlation in males between badge size and hematocrit, but not in females. As individuals with larger hematocrit values can transport more oxygen to their tissues or organs, male badge size may be linked with oxygen transport ability. We suggest that male badge size may be a signal of physiological status.
2017 The Ornithological Society of Japan