The quarterly of the University of Helsinki

Virve Pohjanpalo

Back to spring issue 2006

The severe winter is one of the things that Finns feel forms their identity, an excellent explanation for both the Slavic melancholy and the mythical perseverance. In folk and pop songs migratory birds are suitable for interpreting both feelings: The heart swelling with joy when the migratory birds return because it will soon be summer – or wondering at the early-returning larks’ hurry to the cold north. The verses written by the national poet Eino Leino in a moment of melancholy have been imprinted in everyone’s mind. Leino urged people to learn a lesson from the Whooper Swan, the national bird, which “leaves in autumn, returns in spring”. What would it do here in winter in the flowerless, joyless land?

Magnetic crystals in brains and eyes

It feels both magical and heart-warming at the same time that the same warbler returns year after year to the nest box in the tree in the garden. Moreover, the more general interest in observing and recording migrations is huge in Finland. There are hordes of dedicated amateur researchers in the field.

The movement and breeding of birds is researched in the Ringing Centre of the Finnish Museum of Natural History. Mirja, an Osprey fitted with a satellite transmitter and researched by the Centre’s former director, became a star of the national media (see p. 6-8). “Besides the celebratory bird, cranes, swans and other showy migratory birds awaken especial interest,” says Jari Valkama, curator of the Centre.

“The migratory bird information based on the ringing and reading the rings mainly comes from the amateur birders. For example, Whooper Swans were installed with collars in the 1990s the information on which an amateur birder can read even a long distance away.”

Eyes, binoculars and reading the information obtained from rings are, according to Valkama, the foundation on which to build a thorough knowledge of migratory birds. Satellite tracking, requiring expensive and bulky equipment, is not widespread enough to be able, for the time being, to reach general conclusions. The traditional method of natural history, building test settings, is often poorly suited to the subject.

The restlessness in birds brought on by approaching migration has been researched experimentally but Valkama looks at the results from a slightly critical distance. “How naturally do birds behave when they are caged?” he asks.

The uncertainty factors do not concern the results of all the restlessness experiments. They have confirmed, for example, the ideas about magnetic instincts of birds. The Garden Warbler, for example, has been shown to have magnetic crystals in its brain which help in navigation. Researchers assume that the magnetic substance gives the bird turning its head signals telling about the Earth’s magnetic field and thus about the directions.

Familiar shoreline guides the bird

Magnetism alone is not enough, however. “For example, the stages of Finnish raptors are determined to a large extent by the winds. They migrate during the day and look for a route where they can easily glide. Visual landmarks help on such a journey. The shoreline, highways or other visual hints are most important when the birds are approaching their destination.”

The story of little passerines flying from Southern Africa to Northern Europe is altogether different. “The Swallows, that familiar bird under the eaves, returning to the same farm over and over again are an amazing example of migration. The journey across two continents is huge!”

The little insect-eater’s journey takes place at night so it cannot rely on its sense of sight, unless the star chart and its particular fixed point, the North Star, is good enough. “The downside to stars is that there are many cloudy nights,” says Valkama. “In addition to magnetism and sight, birds navigate at least with the aid of some kind of navigation mechanism, as well as by taking a permanent direction reading. In practice, navigation means that they must have some ready concept of the destination, which requires in turn a tremendous sense of time and place.”

It is very difficult to imagine how a young bird preparing to migrate for the first time can picture its destination. “The first migration does not always take place in the company of older birds since birds of different age groups typically migrate at different times in autumn or spring. Learning therefore does not explain the ‘knowledge’ they have in advance.”

A partial explanation of the ‘knowledge’ is found in genes, to which a migration timetable is programmed in addition to the migration route. Side by side with the genetic ability, however, there appears to be accumulated experience.

“For example, they conducted an experiment in the Netherlands in which a giant flock of Starlings was transferred away from the correct migration route. Birds’ ability to make corrective movements depended on their age. Immature birds often continue in the same direction they were flying after they strayed. Experienced birds were better able to compensate for the ’mistake’.”

Open questions

Valkama’s summary of birds’ migration skills is that one cannot generalise. The bird’s age and species decide it. And there is much still unknown. For example, the accuracy of the bird’s inner map can only be guessed at. “Swans and geese, for example, winter in families. For most of the other species, we do not know how close females and young generally winter.”

Climate change also gives rise to important, still unanswered questions. The information gathered by amateur birders shows that birds are returning earlier to Finland and wintering can take place farther north, according to Valkama. But is it just a question of individual birds’ learning ability or a greater change: evolutionary adaptation to circumstances?