Rooks, it seems, do a little digging under certain circumstances. Selous tells about it in his "Bird Life Glimpses." In this book you will find a delightful description of martins building. It almost makes you want to _be_ a martin. It also tells about the work of the sand martins. You will hardly believe how fast they work. The house-martin's nest is more elaborate than the swallow's. This book tells why the house-martins begin work so early in the morning, and why they have to delay their nest-building if the weather is either too wet or too dry. White, in his famous "Natural History of Selbourne," tells how worried he was because certain swallows just _would_ build facing southeast and southwest. Birds, besides being workers of the soil, are great sowers of seeds. Darwin tells how he reared eighty seedlings from a single little clod on a bird's foot. What do you suppose he did that for? You just look it up in the index to his "Origin of Species." Doesn't it seem funny that one of the little farmer birds--a burrower--should go into partnership with a lizard? There is one in New Zealand that does that very thing. He is called the titi. What the titi does for the lizard is to provide him with a home in his burrow, but what do you suppose the lizard does in return to pay for his lodging? Read about it in Ingersoll's "Wit of the Wild," in the chapter on "Animal Partnerships." Do you know why the phoebe bird so often uses moss in building her nest? And how the phoebes that make green nests keep them green? And how Mrs. P. puts a stone roof on her house? You will find all about it in "Wit of the Wild." The same chapter, "The Phoebe at Home," tells why the phoebe bird took to building under bridges, and why she builds in a carriage shed instead of a barn, as the barn-swallow does. "Bird Life," by Chapman, is a guide to the study of our common birds. The beauty about this book is that it has seventy-five full-page plates in the natural colors, with brief descriptions, so that all you have to do is to bring the _mind_ picture of the bird you have seen alongside the picture in the book, and there's the answer! Nobody has written more delightful books on birds than Olive Thorne Miller. "Little Brothers of the Air" is one of them. You couldn't keep your hands off a book with a name like that, could you? Then there is her "Children's Book of Birds," "True Bird Stories," illustrated by Louis Agassiz Fuertes, and "Little Folks in Feathers and Fur," which, as you can see, goes outside the bird family. John Burroughs's "Wake Robin" deals not with robins alone, but with birds and bird habits in general.