In this final episode, we explore the Great Lakes in Spring where animals experience the most extreme and unpredictable temperature changes on earth – from summer highs of 100 degrees to winter lows of 50 below. Spring thaw in the Great Lakes is marked by extreme temperatures swinging from brutal cold to blazing heat in a short amount of time. This transformation has created the perfect environment for an explosion of evolutionary marvels and mysteries as life is forced to adapt to constant change.
Strange glowing rocks found on Lake Superior’s south shore provide a clue as to how these giant lakes were formed by glaciers. As the ice weakens and shatters, tsunamis caused by temperature fluctuations create giant piles of snow along shorelines, some as high as 30 feet, and help us to understand the volatile and mysterious origins of the Great Lakes. Near Lake Michigan, the world’s largest lake sturgeon spawning produces millions of eggs, inspiring tales of ancient sea monsters. Scientists reveal for the first time that wolves are fishing in freshwater for white suckerfish to feed their pups.
Human development forces Massasauga Rattlesnakes on the run in a desperate swim between Lake Huron’s 30,000 islands to give birth to live young. With nutrients scarce on land, a mother moose dives deep to the bottom of the lake to feed her calf. Migratory birds arrive in their millions each spring to breed. Woodpeckers take advantage of rising sap while ruby-throated hummingbirds keep close for a meal.
It’s a land of wonder with weird and unique animal behaviours. A thirty-year-old female salamander – the world’s only photosynthetic vertebrate – performs an epic migration by night through heavy snowfall to breed and lay hundreds of eggs. In the headwaters of Lake Erie, colourful redside dace are the only fish on Earth to have evolved to catch insects in the air. Beneath the surface, weird parasitic mussels imitate minnows to lure their prey and biologists use innovative new science to battle invasive sea lamprey.
The Great Lakes inhabitants are also facing another threat on top of climate change: the creation of a canal has allowed invasive species like the sea lamprey to bypass the Niagara Falls, forcing biologists Drs Anne Scott and Nick Johnson to innovate new techniques for controlling this parasitic fish. The greatest disruptor of the environment is humans, but we can be the agents of positive change.
Ultimately, wildlife’s ability to adapt and thrive in the Great Lakes watershed is a beacon of hope for people fighting to protect the future of the world’s greatest and most important freshwater ecosystem.