For most people migration brings to mind birds traveling south for the winter. The flying V of a flock of Canada Geese is a visible sign of the change of seasons. The truth is migrating animals can be found throughout the animal kingdom, making extraordinary journeys between all sorts of climates. Birds, fish, mammals, reptiles and insects move not only between north and south but east and west, up and down mountains and even between fresh and salt water.
Whether it is brought about by seasonal change or the need to move towards food or weather conditions that are available in another location, migration is an animal’s way of responding to signals that the planet is sending it. The amount of daylight, a dip in temperature, the scarcity of food etc. are all indications that it is time for an animal to pack its bags.
The arctic tern takes the prize for the longest migration known in the animal kingdom. Each year it travels between the Arctic and Antarctica, a round trip of 90,000 kilometres. The arctic tern can live up to 30 years of age which means that in its lifetime it has flown the equivalent of three trips to the moon and back!
Each year the monarch butterfly rides air currents about 3,000 miles from northern summer breeding grounds in Canada to the warmer climes of Mexico. The same butterflies do not return the following year, however. As the monarch butterfly travels north it ‘hops’ between milkweed patches, a few hundred kilometeres apart, laying eggs which hatch in just days. This new generation takes up the journey to the next milkweed patch. It might take four or five generations of butterflies to complete its spring migration.
The American eel not only travels 2,400 kilometres to get to its breeding ground but swims between habitats. The eel spends much of its life in fresh water lakes and rivers but swims out into the Atlantic Ocean where it spawns in the Sargasso Sea. There baby eels hatch and then drift back to freshwater where they mature. While this epic journey has been long been suspected by scientists it has only been recently tracked successfully. You try tagging an eel!
The longest migration by land of any mammal on earth is undertaken by the porcupine caribou. Although summer and winter grounds may only be a few hundred kilometres apart the caribou’s zigzagging route avoiding predators and physical obstacles (some made by humans) may take them over 4,800 kilometres.
The Ruby-throated Hummingbird doubles its weight, retaining fat to be converted into energy during its annual migration between Canada to Mexico. A hummingbird weighing about 4.5 g can fly nonstop for 26 hours at an average speed of 40 km/h. They may arrive a couple of grams lighter but the extra fat allows them to span the Gulf of Mexico with ease.
Climate change is posing a bit of a challenge to migratory animals. Over long periods of time animals are able to adapt to shifts in their natural environment. For some climate change is happening at a much faster rate than they can adapt.
The overall warming of the planet can be observed in those animals that travel between habitats. Some ways in which scientists have noted behavior change:
- Birds are migrating north earlier in the spring and departing for the south later in the fall. In Europe temperatures have altered enough that some birds are failing to migrate at all.
- Insects, birds, fish and mammals are moving farther north than they usually do, to climates that may be warm enough for them but do not necessarily have the food and shelter they need.
- Arctic animals are finding their traditional migratory routes cut off as sea ice melts away.