Bills I

Our most common birds give us great opportunities to examine them in detail. Here’s a close up of a House Sparrow (Passer domesticus). The bony upper and lower mandibles of birds are covered with a horny sheath of keratin, which is why it reminds me of unkempt fingernails, since it’s essentially the same material. The hole at the top is one of two nares, which are like nostrils, connecting to the respiratory system.

(I’ve got about a week’s worth of bird bill posts coming up, mostly of birds captured during fall migration.)