Molting in Birds: Process and Purpose
The avian feather is one of nature’s true wonders, capable of supporting flight, providing protection from the elements, and showing off beautiful colors and elaborate displays in the breeding season. Did you know that birds replace these remarkable structures throughout their lives?
Birds lose and regrow their feathers on a cyclical, or sometimes continuous basis, by a fascinating and vital process called molting. In this guide, we’ll learn about the timing, challenges, and function of this interesting stage of the avian lifecycle. So, read along as we help you get to grips with bird molting!
What Is Molting?
Definition and Overview
Molting is the process of replacing worn and damaged old feathers with new ones, usually once or twice a year. All birds undergo this crucial process because their feathers lose color and structural integrity over time.
Before molting, bird plumage may be pretty pale or bleached and often visibly ragged or worn. During molt, birds may not look much better, often taking a patchy appearance or showing various missing or half-grown feathers.
When the time comes, a new feather will begin to grow in the follicle, forcing the old one out. Molts typically occur in specific time frames and patterns on the body, although this varies with bird size, habitat, and lifestyle.
Continue reading to learn about some common types of molts.
Types of Molting
Birds can replace lost feathers immediately, but they don’t simply molt them at will. Instead, birds use various seasonal or cyclical molting strategies typical of their species.
In a complete molt, a bird replaces all of its feathers, unlike in a partial molt, when birds only replace some of them. Some birds will go through a single complete annual molt each year, while a few species have evolved to molt their feathers twice (biannual molt) each year.
Many seasonally colorful birds have a single complete molt each year (postbreeding/ prebasic molt) and a partial molt before the breeding season (prebreeding/ prealternate molt) to make themselves more attractive to potential mates. This ornamental breeding plumage is known as the alternate plumage, while the typical plumage seen during the rest of the year is known as the basic plumage.
Birds also go through different molts depending on their age. The first molt is known as the postjuvenile molt, where birds lose their juvenile feathers and may attain adult plumage or an intermediate stage typical of long-lived birds like Herring Gulls and Golden Eagles.
Birds go through different molts depending on their age. American Herring Gull (first winter plumage)
The Stages of Molting
Pre-molting Phase
The pre-molting phase typically occurs during nesting for birds that molt at regular intervals. Raising their young is an energetically taxing part of the year, and molting simultaneously would only compound the problem.
Many birds also perform partial molts to get into fresh nuptial plumage before finding a mate. Hormonal changes triggered by changing day length trigger the development of reproductive organs and stimulate these prealternate molts.
Active Molting
Different birds follow different sequences of feather molts. Some birds replace all their flight feathers at once, while others replace them very gradually, sometimes taking more than a year to complete a molt. Most species follow a regular molting pattern evolved to limit the impact on their day-to-day life. In songbirds, flight feathers are molted in patches or tracts so that the birds do not lose the ability to fly.
Birds become quieter and more secretive while actively molting, and they may look pretty untidy or even be difficult to identify when you do spot them. They may have open spaces between their flight feathers or show patchy colors and patterns caused by the growth of fresh new feathers.
Post-molting Recovery
The period after molting typically coincides with the next major challenge in a bird’s lifecycle. In many species, this involves a lengthy migration to distant overwintering grounds, which is an energetically costly and often perilous journey. However, some birds molt at staging grounds during their migration, while others migrate only after reaching their non-breeding habitat.
Species that develop seasonal breeding plumage usually time their molt to coincide with the start of the breeding season. Spring typically brings an abundance of food, but reproduction also demands high energy expenditure during courtship, nest construction, incubation, and chick-rearing.
Different birds follow different sequences of feather molts. Most species follow a regular molting pattern evolved to limit the impact on their day-to-day life. Anna's Hummingbird
Species that develop seasonal breeding plumage usually time their molt to coincide with the start of the breeding season. Northern Cardinal
Biological Purpose of Molting
Feather Wear and Tear
A fully grown bird’s feather is no longer nourished by the vascular system and does not contain live cells. Without an oxygen and nutrient supply, it cannot heal itself or regenerate if partially damaged.
Exposure to the elements, friction against other feathers, and abrasion against foliage and other surfaces in a bird’s environment cause constant wear and tear on feathers, affecting their color and reducing their ability to ‘zip’ together and create a weatherproof covering.
Seasonal Adaptation
As mentioned, many birds molt and replace their plumage with ornamental nuptial feathers to show off their health and fitness and increase their chance of successful reproduction. Alternate plumage helps birds impress the opposite sex and can be used in territorial displays to see off the competition.
Molts also have more practical applications, especially for birds that live in highly variable habitats. Rock Ptarmigans, for example, develop pure white plumage for the winter that helps them blend in with their snowy environment.
Seasonal molts don’t only alter the appearance of a bird’s plumage. Resident bird species can also develop a much denser covering of feathers to keep them warm in the colder months.
Molting and Bird Behavior
Behavioral Changes
Ducks, Geese, Loons, and Puffins are birds that molt all their flight feathers at once. This molting strategy necessitates drastic behavioral changes because the birds are rendered flightless for at least two weeks of the year! These birds can afford such a risk because they are at home on the water and can move around and forage in relative safety from terrestrial predators.
Other birds molt their feathers gradually to maintain the ability to fly. However, fewer feathers means reduced flying abilities, leaving them more vulnerable to predators. Some molting birds may have to change their foraging behaviors to adapt to their reduced agility during this time.
Feeding and Nutrition
Molting places an extra energy demand on birds, which means they have to eat more while molting than at other times of the year. However, Penguins cannot swim and hunt without a complete covering of waterproof feathers, so they are forced to undergo a rapid and complete molt while fasting. These birds pile on fat reserves during the pre-molting stage to see them through this difficult time.
Ducks, Geese, Loons, and Puffins are birds that molt all their flight feathers at once. This molting strategy necessitates drastic behavioral changes because the birds are rendered flightless for at least two weeks of the year! Puffin on clifftop
Health Implications of Molting
Stress of Molting
The average songbird has several thousand feathers, and this number rises drastically in large birds like Swans and Penguins. Collectively, their feathers may make up over five percent of their body weight, so replacing them each year is no small task!
Growing new feathers requires extra energy input from fat stores or increased food intake, all at a time when a bird’s physical performance is reduced. The physical stress of molting may also increase the risk of predation, but birds limit these risks by adopting secretive habits and molting their flight feathers at a time of year when food is still abundant.
Disorders Related to Molting
Birds may be susceptible to various health concerns related to molting. Factors like poor diet can affect the quality and pigmentation of replacement feathers, and unusual molting patterns can potentially result in secondary problems like infections. Some viruses that affect captive birds also cause delayed molt or unhealthy new feathers.
Molting in Captive Birds
Care Requirements
Molting is energetically taxing, so captive birds need excellent nutrition during this vital and stressful stage of their lifecycle. They may also require more food than at other times of the year, so pay extra attention to your bird’s diet and nutrition during the molt.
During this phase, a bird may become quieter and less active. Limit stress on the bird by keeping it in a comfortable, peaceful environment and keeping disturbance to a minimum.
Observation of Molting Patterns
Molting is a fascinating process that bird owners have a unique opportunity to observe from start to finish. Keep an eye on your bird during its molt to monitor its health, but consider consulting a veterinarian if you are concerned about the health of your bird during the process.
Growing new feathers requires extra energy input from fat stores or increased food intake, all at a time when a bird’s physical performance is reduced. Yellow-eyed Penguin during molt
Summary
Regular or continuous molting is vital for everyday bird survival. While molting patterns and strategies vary significantly across the world’s diverse avian species, no wild bird can perform their full range of natural behaviors without a set of functional feathers.
Molting also makes birdwatching even more challenging and interesting! This process results in the dramatic transformation between juvenile and adult, and breeding and non-breeding plumages we see in so many bird species.
Studying feather molting offers many fascinating insights into the adaptive strategies of birds from different families, habitats, and ecological niches. As we learn more about bird molting patterns, we discover more and more about the delicate trade-offs between replacing worn feathers and the harsh realities of survival in the wild.
So, next time you spot a bird looking a little patchy or flying clumsily on partially feathered wings, consider the challenges it’s going through and the importance of this tough but temporary phase of its lifecycle!