Surviving in Winter

Have you ever wondered where Mute Swans go in the winter or if they stay, how they survive?

Swans do not migrate as far south as the southern US and bonded pairs will try to stay in their territory to defend it for the next nesting season.  But they will migrate as far south as they need to to find open water in winter.  They must have water to drink, preen, avoid predators, and access the underwater plants that are their primary food source.  In Ontario, Canada, this usually means Mute Swans flock on the shores of the Lower Great Lakes.

If even that water freezes, they are at greater risk.  In the very cold winters of 2014 and 2015 there was higher mortality among Mute Swans, who starved to death when most water froze over.  

But even if they stay in areas where the water is not frozen, winters can still be extremely cold.

Swans have several mechanisms to cope.

• They have excellent insulation in their thick layer of down, which is underneath their outer feathers.
• Their necks are the mostly densely feathered parts of their bodies, exposed as they are to the elements and frequently submerged in water.  Of Mute Swans’ total 25,000 feathers, 20,000 can be on their necks alone!  For further warmth, they often sleep with their neck on their bodies.
• They also often tuck their beak under a wing, which not only keeps it warm but means the swans are breathing warm air.
• You will often see them sleeping or standing on one foot, with the other under a wing for warmth.  But their feet are actually built to stay warm.  Many birds, including swans, have a “countercurrent heat exchange” circulatory system in their legs and feet. This means that the arteries (which carry the warmest blood, coming from the heart) and the veins (which carry cooler blood back to the heart) are very close together – almost intertwined. The proximity helps warm even the venous blood and keeps their feet from freezing.  It also means the blood is warm returning from their feet to their heart.
• When preening, swans are cleaning their feathers but also spreading oil over them from a gland near the base of their tails (called the uropygial gland). This maintains their waterproofing which is especially critical in winter and keeps the cold water from reaching their skin.