Resumen de Tree Sparrow (Passer montanus) with an extra wing flight-feather
Abnormal numbers of flight-feathers in the wing have rarely been reported, especially for passerines. On 10th September 1992 on adult Tree Sparrow undergoing a complete moult was caught at Deltebre (Tarragona, NE Spain]; it had on extra flight-feather in both wings. These feothers were probobly secondaries in active growth, each inserted between the innermost secondary and the outermost tertial. Therefore, in each wing this bird showed 20 flight-feathers, rather than the 19 shown by most passerines
