The Mystery of Migration

Each spring and fall, a large number of birds make an annual migratory journey. In the fall they depart the mountains for warmer winter climes. The following spring, they return to the north country to nest.

Similar to the many Canadian who head south to avoid the winter, many of the areas birds will also follow suit. Not only are many of our local waterfowl heading to warmer climes, but we often have the opportunity to see some of our northern neighbours as they pass through.

Migration is nothing new. Thousands of different species of animals follow annual migratory journeys--what makes the journeys undertaken by birds so remarkable is their scale. Some species travel as far south as South America before finally alighting in one area for the winter months. One arctic tern was found to have traveled over 15,000 km in just a few weeks. This migration will be repeated, as it has been for thousands of years each fall and spring.

Migration originated during the last 60 million years as climates changed and brought about the need to move with seasonal variation. During the glacial periods, many of the northern species were forced to move southward by the invasion of ice. However, it is also likely that they took advantage of milder periods between glacial advances and moved back onto their former ranges.

Migration comes about as the combination of climate and a variety of physiological conditions within certain birds. Migrations appear particularly well developed in the cooler areas of the Northern hemisphere, and in all cases, the migration occurs in the direction of more favourable living conditions.

Migration is very difficult to study. The most obvious method is through personal study in the field. By noting the presence of various species, their direction and numbers, along with behaviour and any other characteristics worth recording, provides us with information regarding these seasonal movements. Bird banding, the placing of a small numbered band around their ankles, also helps as birds appear thousands of miles from their banding sites.

They don't seem to be restricted to staying at low altitudes either. Cranes have been seen at altitudes of 5,000 metres and even crows have made it up to 2,500 metres. Geese have been seen as high as 9,000 metres in India. Not only do they head up to great heights, but they tend to fly faster than normal. Swallows flying speeds tend to increase from 46-51 km/hr to between 54-60 km/hr.

Birds use a variety of methods to determine their location during migration. These include following the position of both the sun during the day and the stars at night. They can also use other visual clues such as the position of a river. Some scientists even believe they are able to sense the Earth's magnetic field and thus accurately follow the same route each year.

Migration is a fascinating and relatively mysterious aspect of bird behaviour and one which adds colour and the sounds of honking geese to the skies twice each year.