Birds That Can't Fly
Ratites are essentially birds which have no keel to the sternum. The Latin ratis means raft. Because the birds have no sternum, there is no attachment point for the muscles of the wings resulting in these birds being flightless. Most areas of what was once Gondwana have representatives of the ratite family. Gondwana is the name given to the land mass which existed before the southern continents split and drifted apart.
There are two ways of classifying ratites. One taxonomical system considers each group of ratites as a family with all families combined within the order Struthioniformes. The other method gives each family the status of an order.
Ratites are closely related to the tinamous of South America. These are ground-dwelling but not flightless birds.
Many of the ratites are extinct. The elephant bird and moa come into this category. The Aepyornis or 'elephant bird' of Madagascar could exceed 450kg in weight and stand 3 metres tall. At least eleven species of moa were endemic to New Zealand before the arrival of human settlers. The smallest was about the size of a turkey and the tallest of the species stood 3.3 metres and weighed 250kg.
The largest of the living ratites is the African Ostrich. These can reach almost three metres in height and have a weight of up to 159 kg. They can also outrun a horse.
The next tallest is the emu, native to Australia. It is also a fast, powerful runner. It is found mainly on the open plains and woodlands and may be 2 metres tall and weigh up to 60 kgs.
Heavier than the emu though not as tall are the cassowaries. There are three species. They are endemic to Australia and the islands to the north of the continent. Their natural habitat is thickly vegetated tropical forest. Cassowaries are regarded as 'keystone species' as they are essential to the ecosystems they live in. Some plant species in these areas need to pass through the gut of a cassowary before they will germinate. The cassowary has razor sharp talons and should be treated with caution.
In South America, two species of rhea belong to the ratite family. The American rhea is the larger and reaches about 1.5 metres and weighs from 20 to 25 kg. The lesser, or Darwin's rhea, is smaller and lighter.
The smallest of the ratites are the kiwis of New Zealand. There are five species of the birds which are about the size of a chicken. Kiwis are shy and nocturnal. They nest is deep burrows and have a highly developed sense of smell which they use to find grubs and insects in the soil. Their main claim to fame is the size of their eggs which are huge when compared to the body size. Fifteen to twenty percent of the body mass of a kiwi may be made up of its egg. The smallest of the species is the little spotted kiwi which is 40cm tall and weighs 1.2kg.
Many physical characteristics are shared by ratites.
- There is no keeled sternum.
- The wishbone is virtually absent.
- The breast muscles are underdeveloped.
- The skeleton and musculature of the wing is simple.
- Except for the femurs, the leg bones do not have air pockets.
- The legs are strong.
- Tail and flight plumage have retrogressed and may serve as decoration only.
- They have no preen glands as the feathers have no vanes and do not need oiling.
- They have a palaeognathous palate which means they have freedom of movement between segments of the palate and the jaw.
The ratites are a fascinating group of birds and have had a long relationship with humans. The eggs were used as containers, for jewellery and other arts. Ostrich feathers were popular for hats and boas. This led to ostrich farming and the utilisation of the hides, eggs, feathers and meat. Emu farming provides the same products plus the highly popular emu oil. Dusters are made from rhea feathers. The meat and eggs of the rhea are used in South America. The hides of all ratites are used to manufacture leather goods.