The Case of the Dinosaur Birds — John R. Erickson

It's scrap day on the ranch -- a glorious day for Hank, his sidekick, Drover, and Pete the Barncat. But when two very unusual-looking creatures fly overhead, the glorious day takes a sudden turn for the worse. Suddenly the scraps have vanished, and the Head of Ranch Security finds himself dealing with an invasion by a couple of ancient dinosaur birds! There's never a dull moment when Hank the Cowdog is around!