Abstract: An animal birth detector is described comprising apparatus attached in the proximity of the animal's vulva for detecting the birth of the animal fetus by monitoring the size of the vulva during the period prior to and during delivery of the fetus. More specifically, the animal birth detector comprises a transmitter attached to the skin proximate one side of the animal's vulva, the transmitter utilizing a reed relay switch to sense the proximity of a permanent magnet located on the opposite side of the vulva. As the vulva dilates at time of delivery of the animal fetus, the magnet is moved out of the magnetic field sensing area of the reed switch, turning on the transmitter whose transmissions are received by a receiver monitored by the stockman. The transmitter and magnet are held in place on the animal's rear section by an adhesive coated or sutured vinyl holding pad.