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Bird migration is one of the most awe-inspiring events in nature. The annual peregrinations of some species are nearly unimaginable. At one time, the idea that birds would move from one continent to another was considered so far-fetched that, for example, the disappearance of swallows from Europe in fall and their reappearance in spring was explained by the belief that they hibernated in mud. The truth is often scarcely more credible. For instance, recent research using satellite telemetry has shown that some Bar-tailed Godwits fly nonstop from Alaska to New Zealand, a distance of over 11,000 km, without stopping.
How birds navigate is still a subject of study, but it appears that they use visual cues on land and in the night sky, follow more experienced birds, and sense variations in the earth’s electromagnetic field using molecules in their eyes that are linked to the thalamus, the portion of the brain responsible for processing visual information; in other words, they can actually see electromagnetism.
Many bird species are programmed to migrate geometrically, flying a predetermined distance in a predetermined direction, then turning at a predetermined angle and repeating the process until they reach their destinations. Some individuals are born “dyslexic” and turn at mirror images of the correct angles, resulting in the vagrancy that so delights birders.
Sounds
Birds create an amazing array of sounds, and our world would be very different and much the poorer without them. As a rule, bird sounds are species specific, and many ornithologists and birdwatchers detect and identify birds largely by ear.
There are two basic types of bird vocalizations: songs and calls.
Songs generally perform the functions of territory establishment and maintenance and mate attraction and are usually limited to males and most heightened early in the breeding season. Some birds of dense habitats, especially in the tropics, may perform elaborate singing duets between mates. Only songbirds (Order Passeriformes, which makes up about half of all living birds) possess a syrinx, the organ that produces true song, though some other birds produce sounds that function in the same way as song and not all songbirds actually sing.
Calls are generally simpler in structure than songs and may have various meanings such as pair or family contact, alarm, and even predator harassment. Many birds make non-vocal sounds with their wings, tail, or beak; some of these sounds are the result of feather design modifications.
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Fijian red-breasted musk parrot (Prosopeia tabuensis), also known as the red shining-parrot. © Paddy Ryan
The current status of the Fiordland crested penguin (Eudyptes pachyrhynchus) is vulnerable due to its small population. © Paddy Ryan
Yellow-bibbed lory (Lorius chlorocercus), Solomon Islands. © Paddy Ryan
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