Mating System in birds is very complex . A bird ( Usually its males) has to go through an elaborate ritual to attract the opposite sex. For doing this the bird has to go through anatomical changes, behavioural changes and some times both. Before getting to know about the rituals let us look at the type of pairing that happens in the Avian species.
Mating is a process by which the male impregnates the female with reproductive cells . The result of this is the birth of next generation of the species. Now for calling mating a success , one might just look at the birth of the chicks. But in actual reality the success is when these chicks grow and they in turn mate and produce the third generation, because then only the DNA of the first generation has been propagated. So when a bird becomes a ” Grandpa or Grandma” we can consider their mating as a success and so on.
The pairing up of birds can be broken down as Monogamy and Polygamy ( Polygyny and Polyandry).
This is where a bird pairs up with only one partner and produces a clutch of next generation. This could happen for one season ( Most common like Larks, Munia, Prinia )
or for Couple of seasons ( fairly common like Doves, Pigeons)
For life ( very few species like Saras Cranes)
Monogamy is more prevalent in birds than mammals. The monogamous relationship is not only about the mating, it extends to the male doing other duties like helping in incubation, protecting the nest, Feeding the chicks etc. So the relationship starts with the pairing and can end with the chicks ready to leave the nest.
Monogamy is also fraught with the male getting into “extra marital affairs” , this is called “Extra Pair Copulations”. This happens when the female has eggs in her body and is not ready for the next round of mating, the male will go out and look for females that have had unsuccessful mating and hence are not impregnated yet. These males will come back to their original mates as soon as they have laid the eggs leaving all other affairs they had in the meanwhile. (Example : Great Tit)
The advantage for the male is that he has used the breeding season properly yo propagate his genes, the advantage for the females in ” Extra pair copulation” is that they get impregnated by a male who was not their first choice. The disadvantage here is that the female is alone to tend for the chicks born out of such pairing
When a bird pairs up with Multiple partner in a breeding season , it has said to have entered polygamy. There are two types of Polygamy
Polygyny : When the male of the species has multiple female partners he has entered Polygyny .The males attract females basis the recourses they control. This is called the ” resource -defence Polygyny”. The different types of polygyny are
Location- Defence Polygyny: This is exhibited by birds like Baya Weavers who control an area which is rich in food source and safe for nest building . They defend this territory from other males and this attracts the female to the males. The male’s job ends with nest building and impregnation and he doesn’t take care of the female or the chicks. But since the area is well protected from predators and has rich food source that the females do not mind pairing with these males . The females realise that these disadvantages outweigh the advantages of a faithful partner in a poor resources location area.
Female -Defence polygyny : in this type of Polygyny the male maintains a ” harem ” and will defend the females from approaches of any other male. Here too the females will have very little help from males in looking after the brood but the advantage is that the chicks will have very strong genetic material, as only a very strong male can defend and maintain a ” Harem”
Another system of polygyny that is different from the resource based one is called lekking
This is the system where the Female of the species has Multiple partners in a breeding season. The females practicing this system are more colourful , aggressive and have better vocal repertoire. It is also observed that the sex ratio in polyandry practicing species is highly skewed towards number of males in the species , hence the fewer the females more their power.
The females divide and protect territory basis the food sources and number of males they have to maintain. The Polyandry can be of two types
Simultaneous Polyandry : The female will mate with males in the territory and lay eggs in designated nests built by males . The females will also help in defending the nest and relaying any spoilt clutch of eggs. Example : Bronzed winged Jacana
(For knowing more details on this behaviour of Bronzed winged Jacana pls refer http://ogaclicks.com/wordpress/blog/2016/10/23/the-chudail-witch/)
Sometimes the eggs are all laid in a common nest by many females and this mixed clutch of eggs is incubated , protected and the chicks are reared by Males and females together . This is called ” Cooperative Simultaneous Polyandry” Example : Egyptian Vultures
Sequential Polyandry : The female will go around each individual nest of the males and mate with them, lay their eggs and then terminate the relationship. They will move on to the next male and continue the process . Example :Red Phalarope
In either polyandry the male is the principal care taker, incubator and food gatherer for the nest. The females job is only to lay eggs. Why do males do all these so called ” Women oriented Jobs”, because there are very few females compared to males , and this skewed sex ratio makes the females more in demand. Also the females abandon the males holding a nest full of eggs and the male has no choice but to ensure that the next generation comes out. But nature has been benevolent to the males too, the chicks of these species are Precocial, that is born with open eyes and ready to leave the nest very quickly.
How the mating rituals happens is a chapter by its own, pls refer http://ogaclicks.com/wordpress/mating-in-birds-part-ii-wooing-the-partner