A most important period in the life of any hawk arrives when she begins to undergo the ordeal of moulting. The annual or biennial change of plumage which occurs naturally in almost all birds affects more or less powerfully their health and condition, robbing them for the time of a certain amount of their strength and vigour, as well as depriving them of a part of the actual mechanical apparatus which serves as their means of locomotion. Thus we have seen that skylarks, when putting on a new set of feathers in August, are very much less able to escape from a hawk than when that process has been completed. To the hawk, whose very subsistence depends mainly upon his flying powers, it is obvious that the loss of any big feathers in the wing must be at least a very serious inconvenience, especially if it is combined with a weakening of the whole bodily organism. Nature has not, therefore, allowed the young hawk to mate or breed until after the first moult. At the time when he or she would naturally be busied with family cares--that is, when she is nearly a year old--the minor but still formidable effort of moulting is deemed a sufficient trial. Only when, after assuming the adult plumage, she has kept herself through the whole of a second winter is she called upon to undertake the arduous task of feeding not only herself, but also two or three ravenous and helpless youngsters. The first moult of the young hawk is also arranged to take place at that time of year when it is least difficult for her to find her own living. While the big feathers of her nestling plumage are falling out and being slowly replaced by new ones, the bird world is full of newly-fledged quarry, or at least of quarry which are not yet very strong upon the wing. In other words, the moulting of hawks naturally takes place in summer, just when they are most able to dispense with a part of their flying apparatus and of their energy.