A colony of kestrels (Palco sparverius) was established at the Patuxent Wildlife Research Center in 1964 in connection with work on pesticides. The kestrels were acquired from the wild, both as nestlings and as full-grown birds, and were housed in several rows of outdoor pens. Each 50 x 20 ft pen was covered with wire netting and had its long sides in common with adjacent pens. During the first two reproductive seasons, untreated parent birds (dosed birds are not included in this paper) ate eggs and young. Cannibalism virtually ceased after the diet was changed from ground beef or horsemeat supplemented with liver, vitamins, and minerals to one containing a finely ground mixture of laboratory rodents, chicken heads, skinned chicken necks, and supplements; hatching success thereafter generally equalled that of a wild population. In 1967, 16 pairs of untreated hawks (3-year-old females) laid clutches averaging 4.9 eggs, hatched 88 percent of their eggs, and fledged 88 percent of their young. In 1968, 10 pairs of this group (4-year-old females) laid clutches averaging 4.9 eggs, hatched 51 percent of their eggs, and fledged 85 percent of their young. Nine yearling pairs (hatched in captivity) laid clutches in 1968 averaging 5.1 eggs, hatched 87 percent of their eggs, and fledged all of their young.
