Clare Stone 
Although some birds moult throughout the year, August is prime moulting time for UK garden birds. It’s after the breeding season, before migration (for those that do) and the weather tends to be warm, so a lack of feathers isn’t quite so much of a problem. The moult is a challenging time for our birds, so let’s find out a bit more about the process and who we can support them through it.
What is the Moult?
The moult is the process through which birds shed old feathers, worn feathers and damaged feathers and grow new ones. Just as humans lose and re-grow hair. In birds, each feather grows from a follicle, just as human hairs do.
When a new feather is growing it will push the old feather out, and this is the bird moulting.
Because feathers are individually so much larger than human hairs the process of moulting is much more visible in our garden birds. It makes them vulnerable too.
Where we can just pull on a hat if we are having a bad hair day a moulting bird doesn’t have that option and is far more exposed to the cold.
Losing flight feathers can also make a bird vulnerable to predators until the new ones have grown fully.
This is why birds tend to keep a low profile during the moult and often seem to stop singing in an effort to avoid drawing attention to themselves.
Why Do Birds Moult?
Feathers are truly amazing structures – but they are also dead tissue, just like our own hair and nails.
This means that an individual feather if damaged or worn down, cannot repair itself. The bird must replace it with a new one.
A bird’s feathers do a huge amount of work so it’s easy to see how they might become damaged or worn. Flying, nest building and the general day to day wear and tear of feeding and roosting in amongst trees and undergrowth and exposure to the elements can all take their toll.
Interesting light coloured feathers are less strong and wear more quickly than dark ones as they lack melanin, a pigment that strengthens cells.
Young birds also moult when they replace baby or juvenile feathers with adult plumage. These may often have different colourings, which could signal, for example, that the bird’s plumage can indicate that it is old enough to mate. Baby birds often lack fully formed flight feathers when they are young, these appear later, after they have moulted.
How Often Do Birds Moult
Once a year is standard for most of our garden birds.
But not all birds follow this moulting pattern. The bigger feathers are, the longer it takes to grow them and the more energy is taken in the growing process.
So larger species, such as eagles, may hang on to their primary flight feathers for many years.
Some birds also undergo a partial secondary moult in early spring to reveal their mating plumage before the next breeding season.
But using up vital energy on growing new feathers at this time of year can be a risky strategy. So some birds have evolved a different mechanism for changing colour without growing new feathers.
The starling for example has a distinctive pattern of light speckles in autumn and winter, but in spring and summer is iridescent black, blue and green.
The starling doesn’t moult its speckled feathers to replace them with showy iridescent knees for the breeding season. The speckles are pale coloured tips on new feathers grown after the August moult. As these pale tips lack melanin, they are weaker than the rest of the feather and wear away over the autumn and winter to reveal the starlings flashy mating plumage ready for the spring.
How Long Does Moulting Take?
How long moulting takes for birds depends on the species and the age of the bird.
Most of our small garden birds take around 5 weeks to moult, with migratory birds being the fastest. They have the most pressing need to relace their wing feathers and other flight feathers before setting off on their long journey.
Can Birds Fly During Moulting?
Generally yes, most birds can still fly during moulting, but it may be more of a challenge for them.
Most birds don’t lose all their flight feathers at once. They will lose flight feathers from each wing and the tail sequentially, and in the same place on each side. So flying is still possible if more challenging.
You can sometimes spot a moulting bird in flight because of the “gappy” appearance of the wing and tail feathers.
Ducks and some other water birds however are so heavy that they become flightless during the moult. This means that they are exceptionally vulnerable and have developed several strategies for dealing with this.
Most ducks stay on or very close to the water when moulting. Many males will moult their colourful head and body feathers first to make themselves less conspicuous. The shelduck does a mini moulting migration to a safe secluded area where she can go through the whole process in peace whilst new feathers grow.
Why Do Our Garden Birds Moult in August?
Late summer is prime moulting time for our garden birds, but they don’t have a date written on their calendars. There is variation depending on the weather, the breed and the sex of the bird.
August is typically a time of plentiful food, it’s after the breeding season but before the cold of winter or migration to warmer climes. It’s the ideal time to undergo the process of moulting.
This year, 2021 we had a cold spring, everything is running late and it would be no surprise to see moulting happening later too.
In many species of bird, males can start to moult earlier than females, who wait to start moulting until chicks are fully fledged.
But in many migratory species, both parents may need to start moulting with chicks still in the nest. So that the process can be complete before they start the journey south.
What Impact Does Moulting Have on Birds?
Moulting is a highly stressful time in the avian year and there are a few good reasons for this.
Cold. Whilst moulting patterns mean that birds don’t lose all their feathers at once, during the moulting period they will be significantly less well insulted than usual. When they shed their down birds are especially vulnerable to heat loss. Even though most of our garden bird species moult in late summer, anyone familiar with English weather will know that cold could still be a serious issue!
Energy. Growing new feathers takes a lot of energy. So does keeping warm in a tiny, poorly insulated body. So does flying with only partially feathered wings. So for a bird, the moult is a very energy-intensive process.
Vulnerability. As birds shed their feathers they become more vulnerable to predators. Although most birds don’t lose the ability to fly completely, even the loss of one or two flight feathers can make a bird less mobile in the air. This is why our birds so often seem to disappear in late summer. They keep a low profile and sing less to avoid drawing the attention of predators.
How Can We Help Moutling Birds?
Moulting is a natural process for birds, part of the annual cycle, so although a scruffy shy moulting bird might look unhealthy to us it’s probably perfectly fine.
But a full moult does pose plenty of challenges for our garden birds and there are a couple of key ways we can help.
Keep the Bird Feeders Full!
Some people ask whether it’s necessary to feed the birds all year round. They suggest that there is so much natural food around during the summer that we shouldn’t need to supplement it with more in feeders and on our bird tables.
But though natural bird food may look plentiful to us in the summer, the use of pesticides and loss of habitat means that even in the summer months birds can go hungry.
We believe it’s important to feed birds all year round. During the moult, high energy food like mealworms, suet balls and sunflower hearts will be especially useful.
Provide Shelter
If you garden for wildlife it’s always important to not be too tidy and let the garden get a bit – well – wild.
During the moult, this goes double as birds need places to shelter from the elements and predators.
So go easy on the Chelsea Chop!
Keep The Cat In
Domestic cats kill around 27 million birds in the UK each year. We can’t do much to protect birds from their natural predators during the moult. But we can at least keep an eye on domestic cats, or put a bell on them.
Check out our guide to keeping neighbourhood cats out of your garden.
Thanks For Reading!
The moult is a fascinating and challenging event that most bird species undergo each year. We hope we’ve given you some insight into what’s going on when the birds start to get scruffy and seem to disappear each year. It’s all perfectly natural.
If If we keep our bird tables well stocked and our cats under control we can help our garden birds get through the process and come out with beautiful new adult plumage.
Do you have questions or stories about the moult? We would love to hear them. Why not leave us a comment below.
