Reproductive physiology and Behavior: Animal reproduction normally follows the interactions of photoperiod, weather, endocrine glands and sex-specific behavior. Photoperiod – the relative length of days and night – stimulate the release of hormones from the pituitary gland, which in turn stimulate the enlargement and respective functions of ovaries and testis. The sex organs, in addition to producing eggs or sperm, also secrete sex hormones. In female birds, estrogens secreted by ovaries ready the oviduct and shell gland for egg production and physiologically prepare the female for a long period of incubation. In female mammals, estrogen prepares the uterus for pregnancy. In males, testosterone secreted by testes initiates the intense courtship and territorial behavior typical of the breeding season.

Most wild birds and mammals require suitable environment for competing the reproductive process. Many species do not breed in captivity because one or more crucial environmental elements are missing; and the physiological and behavioral mechanisms associated with breeding fail. Likewise, in nature, animals that do not obtain territories or adequate food or shelter may experience a physiological shut down of breeding activities. Reproductive needs of some animals may include subtle (fine) environmental features that are not readily apparent to human observers.

Courtship Behavior (Mechanism for attracting mates): Most of the terrestrial animals come together for the process of reproduction Even solitary animals, temporarily come together for the process of reproduction. In solitary animals, the behavior is modified usually involve various kinds of ritualized, submissive or aggressive gestures. Courtship behavior is genetical in nature and is specific for a given species. Courtship display heightens intra-specific recognition, reducing the chances of hybridization. In many monogamous animals, there is a pair bonding – male and female stay together a least a season when a single brood is reared; sometimes, this bonding may last for a lifelong. Polygamy or multiple mating is also seen amongst animals – males mates with several females e.g. deer. Polyandry – a single female mate with many males.

Parental care Animals with large reproductive capacity have very less or hardly any parental care. Animals with low reproductive capacity have very high degree of parental care. Parental care is seen t a great extent in birds and mammals.

Before the birth of a young one, certain behavior changes are seen in the adults. In many species, the females do not tolerate other animals and she prefix to live in separate. Birds and animals that started to give birth young ones start to build nest or live in den. Nest building activity in female animal is stimulated by the increased level of estrogen production in the system. This is also initiates the development of a highly vascularised area in the breast region (brood patch in birds). In mammals female suckles milk to the young ones in the nest or den.

In birds and mammals, the parental care involves nest building, incubation, feeding young ones, sanitation, and defense, etc. These activities are essential to bring up an offspring when it is vulnerable and helpless. The relationship, between the mother and the spring, usually disappears when the weaning process starts. During weaning, aggression of mother toward the offspring starts increasing. It is usually considered as a mechanism by which the female can force the young ones to become independent.