A Growing Population

The Blackfoot Valley Trumpeter Swan population continues to grow with the hatching of 9 cygnets in June!  The same two pairs of swans that produced the first young known to hatch in the watershed in over a century have again nested successfully.  However, that was not always an easy process.

Each pair spent the early spring re-establishing their territory, which included chasing off any other swans that ventured near.  And chasing sometimes meant flying after the intruders for a couple of miles to make sure they got the message.  I watched several such flights this spring, and was glad I wasn’t the one being pursued by those huge birds with the big bills.

In May the female (called a pen) of each pair began laying their clutch of 4-6 eggs.  Unlike many birds, swans don’t actually start incubating their eggs until they have laid all of them.  This insures that the eggs will all hatch at about the same time, which works well for precocial species that leave the nest soon after hatching.

Once incubation began the female sat on the nest for about 35 days, through storms and blazing sun and everything between, only leaving the nest for short periods of time to feed.  The male (the cob) stayed close to the nest, especially when she was off of it, providing protection if need be with his formidable bill and strong wings.

Most birds in the nesting season develop a brood patch, an area of bare skin on their chest where the feathers fall out or are plucked out by the birds themselves.  This allows them to provide direct body heat to the eggs and, later, chicks.  Swans and a few other birds such as penguins and pelicans, however, use a different method.  They place their large webbed feet under their eggs and provide warmth between feet and body.

This lengthy process allowed one Trumpeter Swan pair in the Blackfoot to hatch 3 cygnets, and another pair to produce 6 (quite a good-sized brood for trumpeter swans)!  Of course, their work isn’t finished.  As for most parents, it has really just begun.  For the rest of the summer and into the fall, the cygnets will grow from fuzzy gray balls to slightly smaller, grayer versions of their parents.  The adults will teach them where and how to find food (aquatic vegetation and invertebrates), and try to protect them from predators.  After they’ve learned to fly in the late summer, they’ll follow their parents south in the fall to their wintering grounds.  They will likely return together next spring, and continue to expand the Trumpeter Swan population in the Blackfoot Watershed.