The plans of brooder houses, as given above, are for ducklings from the time they are taken from the machines until they are ready for the cold brooder, or growing house. The young ducklings, when taken from the nest or incubator, are very delicate and susceptible to the changes of the atmosphere; they must be kept very warm and free from chilling. The first three weeks of a duckling's life is the most critical period, and after that time the liabilities of loss are reduced to a very low rate--hardly five to the hundred. The front of brooders for young ducklings should be hung with strips of woolen cloth to keep in the warmth of the brooder. The greatest care should be given them at this period; the duck raisers really consider it the most important part of their work, and after a bird has passed the "critical age" they may be counted on for the market. [Illustration: Fig. 16.--House for breeding ducks, showing water runs.] Usually the care of the ducklings at this age is given to the women. They are more careful of the wants of the youngsters and attend to the detail work religiously. A case is known of a single attendant living, as it were, in the brooder house with the ducklings. She began her work with the morning feed at 6 a. m., and until sundown, when the night's meal was given, she was with her charges. The cleanliness of the brooder and pen was carefully attended to and everything was done to promote the health and comfort of the youngsters. At night they were all in their brooders and as snug as it was possible for them to be. A single neglect in the starting of a duckling will result in loss to the raisers. System is the key to the situation, and there should be no deviation from it whatever. [Illustration: Fig. 17.--Single brooder houses and ground plan.] The duckling goes from the warm brooder house to the cold brooder house. The latter house is planned in a way similar to the former, with the exception of the 30-inch brooders. When the birds are taken from the warm brooder house they are three weeks old and of sufficient age to withstand a cooler temperature. They do not need the extra heat of the warm house, and in it would not grow nearly so well. The size of pens in the growing house is larger, and the ducklings are not crowded so many in a pen. If the birds are to be raised in colonies of one hundred each, the accommodations should be ample for them. It has never been proved to be good policy to crowd the growing stock; it retards their growth and encourages disease.