Birds: a Museum guide
The Bird Display
The display on the mezzanine gallery shows representatives of most of the 140 or so families of birds recognised by ornithologists. Each family, with a name ending in ‘idae’, comprises a distinctive group of birds: thus penguins, parrots and sparrows represent three different families. In general, the display places together birds that are thought to be more closely related.
For example, herons and storks are more closely related to each other than either is to the birds of paradise. However, our knowledge of evolutionary relationships remains in a state of some flux, as molecular data continues to provide information that challenges older ideas based mainly on anatomy.
No species of bird has escaped the need to lay eggs which are invariably tasty and therefore attractive to predators. For the duration of incubation, the eggs of most bird species rest in nests, which come in many shapes and sizes, and often represent a compromise between two conflicting requirements – to provide protection against the elements and to avoid attracting predators.
At the minimalist extreme is the Ringed Plover which lays its camouflaged eggs in a scrape in bare sand. At the other extreme are the weavers whose conspicuous and bulky nests are suspended safely on twigs, often over water. However, this strategy alone is insufficient to deter cuckoos which might lay in the nest. To achieve this, the weavers build a tubular entrance, too narrow for African cuckoos to squeeze through.
Most birds build a new nest each year, and even for a later clutch of eggs the same year. This strategy may help prevent the build up of parasites.
Birds of Paradise
The greatest diversity of birds of paradise can be found in New Guinea. Their diet of fruit, generously available in tropical rainforest, is very rich in fructose. They can satisfy their daily energy needs by eating only for around one fifth of the ‘working day’. As a consequence of this time efficiency, females can rear the young without male help.
The emancipation of males from parental duties has given them the freedom to mate with as many females as possible, which they do with the help of vivid plumage, often shown off by extraordinary communal displays. Although not quite so extravagantly plumaged as the birds of paradise, the cotingas such as Cock of the Rock, and manakins are the equivalent birds of tropical South America.
The oilbird, a fruit-eating relative of the nightjar, lives in South America and Trinidad. Oilbird colonies nest in caves where they emit calls, whose returning echoes guide the birds in the dark. Among birds, only the Oilbird and certain swiftlets are known to use echo-location. This ability is only used for navigation, not for capturing prey, and is much less sophisticated than the technique employed by bats, whales and dolphins.
Because of the demands of flight, birds’ skeletons are usually light, typically accounting for about five per cent of the bird’s weight. To achieve lightness without compromising strength, the bones are not always solid but can be a honeycomb lattice of bony tissue (see illustration, left).
The most aerial species have a greater amount of air within their skeleton; bones of diving birds are denser as buoyancy would be a disadvantage. However, light bones don’t compromise on strength! Note the parrot’s skull and consider that the larger Amazonian parrots, such as the Red and Blue Macaw, can crack Brazil nuts in their bills!
Also worth closer examination is the striking skeleton of the flamingo, especially the position of the knees on this bird – not back to front as often thought, but higher, beside the body. The middle joints are comparable to the human ankle, and the flamingo stands on its toes.
With close scrutiny, a major difference can be detected between the flying and the flightless birds – the existence of a ‘keel’ on their breastbone. This plate of bone is used to attach the powerful wing muscles which enable flight. On flightless birds such as the cormorant (far left in the display case) the keel is all but absent.
With the exception of the Galapagos Penguin nesting close to the Equator, penguins are confined to the southern hemisphere. The sixteen species feed variously on fish, squid and crustacea, sometimes caught at great depths. Dives over 250m have been recorded for the largest species, the Emperor Penguin.
Although penguins live in cold climates, they are protected by superb feather insulation. The fact that snow falling on an incubating penguin often does not melt, illustrates how little heat is escaping from the bird’s body.
The British birds
The display at the rear of the lower gallery shows the majority of British bird species. It is often used by ornithologists for identification purposes. There are a number of birds included here that were once common in East Anglia but are now very rare, such as the Golden Oriole (far left, bright yellow), the Marsh Harrier and Hobby (in the birds of prey section), and the Bittern (top shelf, middle of display).
With species such as skylarks and some plovers also becoming increasingly rare, it may be that, in the future, displays such as this become one of few places where such beautiful birds can be seen.