The Amazing Avian Migration
Doesn’t it seem like just yesterday that spring had arrived and we had the whole summer to look forward to? But here we are, with shorter days, leaves changing colour, and the thermometer dipping once again. These are all cues for us to start dressing with more layers, but these are cues for most birds in this area to start preparing for their migration to the sunny south.
To a human, the idea of seasonally migrating vast distances seems irrational, impractical, and to be a relatively extreme adaptation for an animal. But for birds, it couldn’t make more sense. The simple reason birds migrate is the need to move from an area of low or decreasing resources to an area of high or increasing resources. The summer in Canada offers a plethora of food in the form of fruits, berries, seeds, and insects, but as summer fades to fall, these food sources become more difficult or even impossible to find. It’s not so much the cold temperatures that necessitate the move, but the lack of food associated with winter. Most birds, even the ones who migrate south, can withstand the harsh winter weather, but birds that remain here all winter have adapted to find food in these conditions while migratory birds have not.
One leading theory to describe how seasonal migration became a way of life for most bird species is that it evolved by a gradual extension of smaller annual movements as birds searched for improved food or breeding opportunities. Individuals whose movements gave them better chances to survive and reproduce would have passed that migratory behaviour along to their offspring. What may have started as small jaunts to and from a seasonally-superior feeding or breeding grounds, eventually grew to larger distance journeys as the climate and resources changed over thousands and even millions of years.
One question researchers are asking now is whether migration originated in the north or in the south, and evidence actually seems to support both ideas. It may be the case that some species originated in the north and evolved to fly south for better feeding opportunities in the winter, while other species originated in the tropics and evolved to fly north for better breeding opportunities in the summer.
Other aspects of migration are also still a mystery. What triggers their migration each season is still not completely understood, but likely has to do with a number of factors including change in day length, temperatures, food supplies, and genetic pre-disposition. How birds navigate while migrating is also not fully known, but they are thought to use a combination of senses and cues including the location of the sun, stars, the earth’s magnetic field, landmarks, and even smells.
If you’re not amazed by the remarkable feats of these birds yet, consider that birds who just hatched in Petawawa this summer will fly south, perhaps without any guidance, for thousands of kilometres and find their wintering grounds even though they’ve never seen it before. Next Spring, they will show up back in Petawawa to start the process over again. Most people appreciate the beauty and soundscapes that birds provide us all spring and summer, but sometimes we take for granted the amazing journey these birds make twice each year to do so.
