The most common breeding system in birds is monogamy. This is seen in more than 90% of the species. Here, the sexes pair for one or more breeding cycles and cooperate to build the nest, incubate the eggs, brood the chicks and defend the family against predators. Certain birds like parrots, albatrosses, eagles and pigeons (above: pair of Pink-necked Pigeon, Treron vernans, male below and female above), take this one step further and pair for life. With two birds involved in doing all these activities, the chance of a breeding success is heightened.
The opposite of monogamy is polygamy, seen in only 3% of birds. This involves a male and/or female having more than one sexual partner during one or more breeding cycles. Where it is the male who mates with several females while the females mate with only one male, the relationship is known as polygyny. A good example is the Baya Weaver (Ploceus philippinus).
A polygamous relationship where it is the female who mates with several males is termed polyandry. Typically this involves sex-role reversal where the females are larger and more brightly colored. The males take over the incubating duties and will care for the chicks. This is seen in the Greater Painted-snipe (Rostratula benghalensis) and Red-necked Phalarope (Phalaropus lobatus).
In polygynandry, both the male and the female of the pair mate with more than one sexual partner during a breeding season. Seen in Dunnock (Prunella modularis), this mating system is rare.
Some of the above examples will be described in subsequent series.
Credit: YC Wee (text, green-pigeon image), Johnny Wee (Baya Weaver image).
Erritzoe, J., K. Kampp, K. Winker & C. B. Frith, 2007. The ornithologist’s dictionary. Lynx Edicions, Barcelona. 290 pp.