Cliff swallows have returned to Oklahoma in force! Historically, these “square-tailed” swallows nested on vertical cliff faces and the entrances to caves, but now they’ll regularly use bridges and highway culverts. Mud pellets are collected in the bird’s beaks from nearby streams and puddles and up to two pellets may be added to the nest every minute. A pair can add more than half an inch to their nest rim in half an hour. #OutdoorOklahoma #nature #birdsofinstagram