Birds and mammals are not known to have produced parthenogenetic populations in the wild. But, oddly enough, experimenters working with turkeys have had considerable success in producing parthenogenetic strains. Using more than 42,000 eggs American scientists were able to increase the number of eggs "which started to develop" from 16.7 per cent in 1952 to 41.7 per cent in 1959. This improvement was a result of selective breeding. Birds producing a high proportion of eggs with parthenogenetic tendencies were mated from males descended from other such birds. Towards the end of the experiment 67 embryos were reared to hatching, a few survived to maturity, three produced sperm, and one actually produced off spring. More recently, Patricia Sarvella of the US Department of Agriculture reported the birth of four male parthenogenetic chickens, hatched from 8,532 eggs: all four reached maturity ("Nature", vol. 243, p.171).