In North America a very large percentage of our songbirds migrate surprisingly great distances to southern climes in the Fall and return in the Spring to nest. These birds are referred to as "neotropical migrants". The word "neo" means new and "tropical" refers to the region between the Tropic of Cancer and Tropic of Capricorn. This region includes such places as Central America, Mexico, the Caribbean Islands and parts of South America.

      What triggers the urge to migrate (southward, for example)? A few probable causes are:

      1. Drop in ambient temperature.

      2. Shortening of daylight hours available for feeding. Nights are therefore becoming longer and colder.

      3. Reduction in available food to sustain warmth. Harvest season over; insect numbers dropping.

      4. Possibly some hormonal change.

      Migratory birds have a physical make up different from non-migratory birds. For example they have more robust muscles and the ability to quickly store up large amounts of fat. The bodies of some songbirds may be as much as 40 percent fat as they start on their migratory flight. During migration these fat stores are used up to supply energy for the trip.

      Another requirement for successful migration is for the bird to be able to successfully navigate to its destination. In addition to the following of visual landmarks a multitude of theories abound on this subject such as the use of the position of the sun, moonlight, Celestial navigation using the stars, and the sensing of the earth's magnetic field. Some or all of these methods may be used in combination depending upon the environmental conditions at the time. As most birds, except for nocturnals, are probably sleeping during the nights prior to migration, the question is how could they learn what stars to follow? Possibly on their first trip the younger birds simply follow the veteran travellers. All the other methods (landmarks, sun, moon, magnetic field) seem to have some promise.

      The mechanics of bird migration takes many forms. Birds such as Raptors (hawks, vultures, falcons, kites and other species) deliberately fly only during the day and over land masses to make use of thermals. Other birds such as the Tundra Swans fly between successive staging areas where they stop for extended periods to feed and replenish their store of energy for the next leg. Snow geese are reported to sometimes fly day and night to make the next stopover. The Arctic Tern, travelling the longest distance lands on the ocean to rest and feed during its long trip. from Arctic Canada to the Antarctic seas (over 20,000 miles, round trip)!

      Then there are the songbirds that almost invariably migrate at night and thus introduce the greatest mystery of navigation. These birds travel in large flocks. They have their own distinctive "night voices" which (we think) keeps the flock cohesive on one hand and yet maintains separation of individuals on the other.

      During their trips the migrating birds encounter many natural obstacles such as predators and weather disturbances, from rain and fog to severe storms and headwinds. Possibly an important reason for travelling at night is the avoidance of their natural predators such as hawks. An attack by hawk(s) could certainly cause pandemonium and disperse the group.

      On top of all the natural difficulties are the man-made obstacles which, more and more, are taking a far greater toll than the natural hazards:

      ** Radio and television tower collisions and electrocutions. For example, on 22 January 1998, in Wichita (Kansas), 5,000 - 10,000 birds were killed by tower guy wires as they milled about the tower clearance lights.

      ** Collisions with large buildings and especially the windows of office buildings where the offices are still lit. The birds can't see the glass and crash into it.

      ** Global warming.

      ** Eradication of wetlands.

      With all these dangers, both natural and man-made (described further in the references), it's a wonder that the birds ever manage to complete their long journeys.

HOW THE BIRDS ARE TRACKED

Banding
      Bird banding (the European terminology is "ringing") is one of the most useful tools in the study of wild birds. Wild birds are captured and marked, usually with a numbered metal band placed on the leg. The bander records important information about the bird, and where and when it was banded. some birds are banded while they are still nestlings, before flight. Bands are then observed or recovered at other locations from captured (and subsequently released) or dead birds (disease, hunting etc.).

      The banding of birds began about 1900 and is strictly controlled through international treaties. Central files in Washington, DC contain the data for all birds banded in North America.

      Data from recovered bands provide information on the distribution and movement of species, their relative numbers, annual production, life span, and causes of death. Such information increases our knowledge and understanding of birds and their habits and helps us to manage and conserve them.

      A link to a very informative article on bird banding by the Canadian Wildlife Service webpage is provided in the references below.

Radio (Satellite) Tracking
      Satellite tracking (Global Positioning Systems) of selected single large birds such as Tundra Swans and Snow Geese has recently been used and the results made available on the Internet (see below).

Radar Tracking
      With the use of Radar, the locations of flocks and even individual birds can be tracked to obtain some idea of the population flow as well as using the information for commercial and military air traffic control. The link (below) to the programme in Israel demonstrates the importance of this in an area of migration "choke".

Birdwatch stations (Personal observations)
      Observations and counts by birdwatching individuals and ornithological organizations across the country are collected and compiled to present a growing picture of the migration habits and patterns of various birds and other fauna. The Greater Toronto Raptor Watch is one example. It has stations at Toronto's High Park, Whitby's Cranberry Marsh and at the Heber Down Conservation Area near the town of Brooklyn. The stations operate from late August to late November and monitor the southward movements of hawks, songbirds, dragonflies and butterflies.

North Sea Bird Count:
According to the Phillips Petroleum Company website "A former Phillips physician and avid birder looked at the oil platforms stretching from England to Norway and saw an opportunity to monitor the migration of birds as they cross the North Sea. He established a network of oil industry employees in the late 1970s. Today that network involves dozens of observers living on offshore platforms sprinkled throughout the North Sea."