_Number and Colour of Eggs._--The full complement of eggs laid by a bird is known as a set or clutch. The number varies greatly with different species. The Leach's Petrel, Murre, and some other sea birds, have but one egg. The Turkey Vulture, Mourning Dove, Hummingbird, Whip-poor-will, and Nighthawk lay two. Various Thrushes, such as the {24} Robin, Veery, and Wood Thrush, deposit from three to five, four being the most usual number. Wild Ducks, Turkeys, and Grouse range from eight to a dozen or more; while Quails sometimes lay as many as eighteen. Eggs are variously coloured, and some are so marked that the blending of their colours with those of their surroundings renders them inconspicuous. Thus those of the Killdeer, Sandpiper, and Nighthawk, for example, are not easily distinguished from the ground on which they lie. Many eggs that are laid in holes or other dark places are white without markings of any kind, as illustrated by those of the Chimney Swift, Belted Kingfisher, and all Woodpeckers. In such instances Nature shows no disposition to be lavish with her colouring matter where it is not needed. _Behaviour When Nest Is Discovered._--After the young are hatched it is even easier to find nests by watching the parents. The nestlings are hungry at all hours, and the old ones are visiting the nest at frequent intervals throughout the day. Birds {25} behave very differently when their nests are discovered. A Cuckoo will glide away instantly and will make no effort to dispute your possession of her treasures. A Crow will also fly off, and so will a Wild Duck and some others. On the other hand, the Mockingbird, Robin, or Shrike, will raise a great outcry and bring about her half the birds of the neighbourhood to pour out on you their vials of wrath, unless you have the good judgment to retire at once to a respectful distance. Warblers will flit from bush to bush uttering cries of distress and showing their uneasiness. The Mourning Dove, Nighthawk, and many others will feign lameness and seek to lead you away in a vain pursuit. A still larger number will employ the same means of deception after the young have been hatched, as, for example, the Quail, Killdeer, Sandpiper, and Grouse.