While the land on these plants is heavily stocked with poultry, the birds are on it only half of the season,--when vegetation grows freely,--and during the remainder of the season a great deal of manure is removed from the soil by gross-feeding crops like rye and cabbage. So the land may be heavily stocked longer than it could be if fowls were on it all the time. The chickens grown in this way do not usually grow so large as those that are given more room, but they are grown at less cost and are as large as the market demands. By this method the land will carry a large crop of chickens year after year for many years, yet it finally becomes so contaminated that chickens do not thrive on it. [Illustration: Fig. 116. Group of houses on a Petaluma egg farm. (Photograph from Bureau of Animal Industry, United States Department of Agriculture)] INTENSIVE EGG FARMING Still another important development due to artificial incubation took place in California. The climate of the Pacific Coast is well suited to fowls of the Mediterranean class, the cold never being severe enough to affect their large combs. Hence these fowls early became very popular with farmers in this section, but as they were non-sitters, those who kept them had to keep hens of another breed to hatch and rear the chickens. When an incubator factory was established at Petaluma, California, the farmers in that vicinity began to use incubators, and some small egg farms grew up in the town. White Leghorns were kept almost exclusively. Before long the egg industry here had grown to such proportions that it was the most important local industry, and the district became celebrated as a center of egg production. Although the product is different, and a different type of fowl is used, the conditions at Petaluma closely resemble those in the roaster-growing district of Massachusetts. The special egg farms are small, each containing from five to ten acres. The houses for the laying hens are larger than the colony houses used in Rhode Island, and are arranged in groups of three, each group containing about five hundred hens. The egg farmers grow their own pullets but, as a rule, do not breed or hatch them. The hatching is done by custom hatcheries, the eggs coming from flocks of White Leghorns on farms that do not specialize in poultry but keep a flock of Leghorns under more favorable conditions than exist on the egg farms. Here, as in the Massachusetts district, the bad effects of intensive methods are reduced for a time, because the fowls affected by them are not used for reproduction. POULTRY FANCIERS' FARMS