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A case report of bill color aberration in a free-living Eurasian Tree Sparrow (Passer montanus): Morphological and physiological description

ABSTRACT Color aberration in birds is a common biological phenomenon relative to other vertebrates. To date, a large number of avian species with abnormally colored individuals have been documented. Although evidence has shown that color aberration may co-vary with morphological and physiological traits, little information is available on the variations of morphological and physiological traits of free-living aberrantly colored birds. Here we report a case of a free-living female Eurasian Tree Sparrow (Passer montanus) with bleached bill but normally pigmented plumage. We further compare the differences in 5 morphological indices including body mass, body condition index (BCI), length of the bill, tarsus, and wing, and 14 physiological indices including core temperature, hematocrit (Hct), baseline plasma glucose (GLU), total protein (TP), uric acid (UA), total cholesterol (TC), triglycerides (TG), free fatty acid (FFA), beta-hydroxybutyrate (β-HB), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), and creatinine (CREA) between the aberrant individual and other normal birds. Our results show that the aberrant sparrow has significantly shorter tarsi, longer wings, and higher core temperature, lower levels of plasma TP, UA, LDL-C, ALP, and CREA than normal sparrows, while no significant differences were noted in other morphological and physiological indices between the 2 phenotypes. Our results indicate that bill-color aberration in the Eurasian Tree Sparrow may be associated with a few morphological and physiological alterations, especially in terms of thermoregulation and protein metabolism. However, these alterations do not result in dramatic changes in body condition, other plasma metabolites, or enzyme activities.