 Based on the Biblical injunction against cooking a kid in its mother's milk, this rule is mostly derived from the Oral Torah, the Talmud and Rabbinic law.Chicken and other kosher birds are considered the same as meat under the laws of "kashrut", but the prohibition is Rabbinic, not Biblical.The use of dishes, serving utensils, and ovens may make food "treif" that would otherwise be kosher.