Bird
Most bird species are socially monogamous; they usually mate for one breeding season at a time. They may mate for years. It is rare that these birds will mate for life. Other species are polygynous, in these species, one male will mate with many females. Birds species are rarely polyandrous. In these species, one female will mate with many males. Birds produce offspring by laying eggs. The eggs are fertilised by sexual reproduction. The eggs are often laid in a nest and incubated by the parents. Most birds take care of their offspring after hatching. Some birds, such as chickens, lay eggs even when not fertilised. Unfertilised eggs do not produce offspring.