What is that bird? Molting at your backyard feeders
Plumage is the word used to describe the feathers on a bird. It is the variety of plumages we see on bird species that attract us, from the bright yellow of a male American goldfinch in the summer, to the mottled brown and greys of a great horned owl. Possessing feathers makes birds unique from all other animals, as they are the only animal world-wide that has feathers.
Birds
around the world have a variety of different plumages, ranging from very
colourful to very subdued, and each variation has its own purpose. Plumage
colour can vary from species to species, or differ between males, females, or
juveniles of the same species. For example, male house finches are a striking
peachy-red in your backyard, while the females have predominantly grey/ brown
streaks for colouring. Spotted Towhees and Dark-eyed Juncos are great examples
of birds where the juvenile appears similar to the adults but also different as
the juveniles have a surplus of brown streaks compared to their adult
counterparts.
For
some species of birds their plumage will change depending on the time of year,
with the most noticeable change occurring when birds shed their brightly
coloured breeding plumage to don their winter plumage. The bright-coloured plumages
we see on some birds in the summer can take a lot of energy to produce, a
process made easier when nutritious food is naturally available. But as summer
comes to an end birds naturally molt (replace old feathers with new) to become
more energy efficient in the fall and winter, when natural food can be hard to
find. Sometimes post-molt the birds we recognized so easily in the spring and
summer can become harder to identify; for example the once canary-yellow male
American goldfinch will become a greyish-yellow in the winter. Or the European starling,
recognized for its glossy black iridescent feathers and yellow bill, becomes a
black bird with copious white spots and a dark coloured bill in the fall.
Molting
for most birds will happen twice a year- in the spring birds will molt from
their winter plumage to their breeding plumage, and then in the fall they will
lose their breeding plumage in favour of their winter plumage. For juvenile
birds they will undergo a molt where they will lose their juvenile plumage and
start to look more like the adult of their species. For some birds the
transition from juvenile plumage to adult plumage can happen the same year they
hatched, or years later after they mature. When birds molt it can sometimes be
difficult to identify them, as some birds can naturally lose large patches of
feathers before the new feathers grow in, creating bald spots and making them
look a little rough. The good news is that although the birds look disheveled,
they are still able to fly, even if they’re missing a lot of their feathers.
For some birds molting is serious business and can make them vulnerable to predation. Most songbirds will undergo a partial molt in which they only molt some feathers, allowing them to still fly. But for some water-fowl, like Mallards and Canadian Geese, undergo a complete molt, where they replace every one of their flight feathers during a single molt period. During a complete molt you often will find waterfowl staying close to water, as they are unable to fly until their flight feathers grow back. A quick wander around Buttertubs Marsh, you will notice there are no brightly coloured male Mallards or male Wood Ducks, but what looks to be an excess of their female counterparts. Male ducks have what is known as eclipse plumage, where they closely resemble the females after they have lost their brightly coloured breeding plumage.
A
bird’s plumage serves multiple purposes from courting, camouflage or simply to
keep a bird warm when the weather is cold or dry when it rains. Plumage can
also be used for communication, especially during territorial disputes. This
can be seen with male Red-winged Blackbirds that will use the red and yellow spots
on their wings to show dominance in territorial displays with other males. Biologists have used the patterns of molting
feathers to help us understand bird behaviour, changes in nutrition in a bird’s
seasonal diet, and to help us understand how old a bird is. There are a lot of
reasons why a bird will undergo a molt, and types of molting varies widely
across birds species. You can easily witness how birds change their plumage seasonally
by watching the birds visiting your backyard feeder. Over the next couple of
weeks some signs of molting will be obvious, like the colour change for the
male American goldfinch. But for most birds molting will be subtle, perhaps a
couple feathers missing here and there as they all prepare for the change in
season.
