SEXUAL DIMORPHISM

The occurrence of to different morphological forms in specie distinguishes males from females. In birds having domestic chicken as forexample. The to forms are the rooster and the hen .In wild birds, sexual dimorphism is well marked during the breeding season particularly in birds belonging to the order-Passeriformes most distinguishing cheracter is the primate normally in dull color. Two very bright color including exaggerated growth of certain parts of the plumage certain species of birds do not exhibited sexual dimorphism .This is particularly true with bad specie which is monogamous.
Mating system
It can be described as partners of sexual and social relationships resulting in mating between male and female individuals. In animals, they are three mating systems that have been recognized namely;
Monogamy
Polygamy
Promiscuity
In birds, they similarity is as follows;
Monogamy; This is a system in which males and females mate with one partner only during breeding season. This is the most common mating system among birds and 90% of bird’s species.
The existence of this behavior could be due to extensive care of chicks by both parents.
Eggs have to be consistently in incubated and defended against predators.
Chicks require warmth, protection, and continual feeding
In other birds e.g. some African hornbills, parental roles may be performed by different parents.
The nest is built in deep hole within a tree. The female Wales herself inside crevice living are small hole for male to pass food for her the situation persists until the chicks are hatched and grow. Some birds maintain stable pair bonds several years and sometimes for life forexample. crested crane and Egyptian gees. 
 Polygamy. Here an individual of one sex males with several members of opposite sex
Polygamy can also be divided in two different subsystem of mating
Polygny; is a system in which a male meets with several females but it is not widely exhibited in birds.
In birds ,good example are found in the situation .The Males acquire territories up on which many females came to mate with the terrestrials males forexample, the seed eating birds of Africa form territories during breeding season’s like;
Pin tailed whydah, paradise whydah and the bishop males demarked and defend territories in to which females are attracted to meet with the males.
Polyandry. This is the mating system in which a female meets with several males.
In birds the mating systems males
In birds the best sturdy is found in American jacana. A bird similar in morphology in African jacana both belonging to the family jacanae. Female defend large territories which are sub divided in two smaller territories .Each similar territory is in turn defended by a male. Female move from one territory to another for mating with males in these smaller territories and laying eggs. Eggs are entirely incubated by a male defending that smaller territory. Polyandry females are normally larger in size than their male counter parts.
Promiscuity. This occurs in these species which come together only for copulation and then  see no more of each other .Previously forexample, have been in relation family of trochilidae of recent, however, the term is now largely disused in refer ice to the animals except to it human connotation which is considered in a appropriate to other animals.
Note: Animals (man excluded) normally mate when females are reproductively respected to men i.e. during estrous/when in heat which is not the case with man and debit who breed thought the year.