The transition from summer to fall is a special time of year - and no, it’s not because of the pumpkin spice flavors! I’m talking about annual migrations. For thousands of species of birds, insects, and sea creatures, the end of summer signals that it’s time to get moving to warmer habitats.
For some organisms, a migration includes stop points for refueling. Others pull a marathon of migration, barely stopping for food or rest. One species of animal even extends its lifespan just to reach its destination.
The triggers that cause migration are the same for many animals. As winter approaches, food resources become more limited. Sunlight decreases, and plants die off or slow their growing. Prey animals might hibernate, reducing food sources. Migration also brings together large groups of animals to reproduce, helping to protect from inbreeding.
If there’s any rule on how animals travel huge distances, it’s that there is no rule. Here are a few profiles on how animals tackle their migrations:
🐋Humpback whales spend their summers in the cold ocean waters near the poles, where they binge on krill and fish. Once summer ends, the giant mammals make their way towards the equator to give birth and raise their baby calves. The whales might travel almost 8,050 kilometers (5,000 miles) in this process, the longest migration of any mammal, but there are no stops for food along the way. The humpback whales rely purely on their fat reserves during this challenging journey.
🦋 Monarch butterflies famously travel to the Sierra Madre mountains of Mexico from the USA and Canada as fall approaches, then fly back north in the spring. The journey north is an intense one, with multiple generations of butterflies dying along the way. The butterflies travel a few hundred kilometers, lay eggs on a milkweed plant, and die. The process repeats up to five times until they reach their summer destination. What is absolutely incredible is that, in contrast, the butterflies that migrate south pull off the journey in one generation. 😮 The southbound butterflies are a kind of “super-butterfly”, with the ability to live eight times longer (and travel eight times farther!) than their parents and grandparents.
🦅 The bar-tailed godwit bird does not mess around when it is migrating. These birds nest in the Arctic and Scandinavian region and will travel to the New Zealand and Australian coasts for the winter. It was recorded that a young godwit flew from Alaska to New Zealand, traveling for 11 days - straight! Scientists are studying how these birds can sleep while in flight. One explanation is they take super short power naps while in the air. Another idea is that the bird sleeps with one eye open during flight. This would require the bird to turn off half of its brain during this resting phase while the other side stays alert!
🌎 We can't forget about the granddaddy of all the migrating animals: the unassuming Arctic tern. This bird nests in the North Pole during the summer and travels all the way to Antarctica in the winter! It's not a straight shot, either. The tern meanders as it travels, grabbing a meal of ocean fish here and there and stopping to rest. This adds several thousand miles to its journey, creating an average round trip of 80,500 kilometers (about 50,000 miles.) Another interesting fact about the tern: because of Earth's tilt, this bird likely experiences the most sunlight of any other species of animal.
There's still lots to learn about animal migrations. One recent study revealed that painted lady butterflies did not die off during the winter months (as previously believed); they just put thousands of miles between their northern summer homes and their winter destinations in Africa and South America. These delicate-looking insects are hard to monitor because they travel at extremely high altitudes during these trips - demonstrating they are much tougher than they appear!
Here is a graph showing how the migratory distances of different birds stack up. Keep in mind that much like in the human world, traveling by air is a total advantage. The longest migration by land is carried out by the caribou, covering a round trip of about 3,200 kilometers (approximately 2,000 miles.)
If I brought this graph into the classroom, here are some questions I'd have to go with it:
💡If the Arctic tern lives for an average of 30 years, how many kilometers (km) might this bird travel in a lifetime?
💡The Pacific Ocean is 19,800 km across. Which birds on this graph could travel the distance across the Pacific more than once in a year?
💡What do you think makes the Adélie penguin's migration distance so impressive?