Birds

Brood parasites

The egg-layer leaves her eggs with another birds nest, is more common among birds than any other type of organism. After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood.

Brood birds must lay their eggs in the nests of other species because they are incapable of raising their own young. Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks

Bird feathers

Feathers are a feature characteristic of birds. There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematic. Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this.

Migration

Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimizing availability of food sources and breeding habitat.

Land birds have a flight range of around 2,500 km

Shorebirds can fly up to 4,000 km

Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food.

Mating

During breeding season in response to the hormones, the male's testes become several hundred times larger than normal to produce sperm, with the left testis usually larger. The female bird's ovaries also enlarge during breeding season to produce the ovum. Female birds usually only have one functional ovary, the left one.

Over 90 percent of birds are considered monogamous. Most birds keep the same mate for the entire mating season and some stay paired for their entire life. Courtship, generally the male's responsibility, usually entails singing but can also consist of tail drumming or dancing.