The Male Perspective Birds, one of the largest groups of animals that are often monogamous, sometimes demonstrate a behavior known as extra-pair copulation. Also, the alpha female may mate and be fertilized by a beta male while the alpha male is away searching for a partner. It has been shown that males tend to guard their primary mates much more closely during her fertile period and spend time in search of other mates only after this period is over. Whether these extra-pair copulations prove worthwhile for the males involved depends entirely on whether or not a beta female's egg is fertilized. With the use of DNA fingerprinting to determine paternity, it has been demonstrated that extra-pair copulation is advantageous for males and that the beta female's eggs are in fact fertilized quite frequently.
Most females resist philandering males, however some seek out copulation from more than one male.
The table below lists hypotheses on why females might seek out several partners. Hypotheses on why females might benefit by mating voluntarily with more than one male. Reproduced from Alcock, 493. Genetic Benefits of Polyandry 1. Egg fertilization insurance via acquisition of sufficient numbers of competent sperm.