Molting is the process by which birds shed old, worn feathers and grow new ones. It is a normal part of a bird’s life cycle and allows them to maintain their plumage in good condition. Molting duration can vary significantly between bird species, as well as between individual birds based on factors like age, sex, environment, and time of year. Overall, molting lasts anywhere from a few weeks to several months.
What is molting?
Molting, also called moulting, is the process by which birds replace their feathers. Feathers deteriorate over time due to physical abrasion and damage from the sun, water, and other elements. Old damaged feathers impair a bird’s ability to fly and regulate body temperature. Molting allows birds to regrow fresh new feathers for optimal function.
Feathers molt one at a time, with new ones growing in to replace old ones as they are shed. Most birds molt at least annually, although some species molt multiple times per year. Molting frequency depends on factors like the rate of feather wear and strategies for surviving seasonal changes in food availability or breeding conditions.
What triggers molting?
Several factors can trigger the onset of molting in birds:
- Seasonal changes – Most birds molt seasonally before and after breeding seasons or winter. Increasing day length in spring triggers molting in preparation for the breeding season. Decreasing day length in fall triggers a molt to grow thicker winter plumage.
- Hormones – Changes in hormone levels, like decreasing testosterone, can induce molting.
- Stress – Physical or environmental stressors, like food shortages, illness, or habitat issues can prompt molting.
- Age – Birds typically molt more frequently in their youth, with molt frequency decreasing with age.
- Breeding status – Some birds may initiate a molt after breeding seasons.
- Photoperiod – Changes in day length help stimulate molting at optimal times of year.
These factors ensure birds molt when conditions are best for new feather growth and survival throughout the year.
Major types of molts
There are two major types of molts birds undergo:
Prebasic molt
The prebasic molt, also called presupplemental molt, involves replacing most or all feathers. It happens annually and results in fresh basic plumage. The timing varies across species based on factors like breeding status, age, and environment.
Prealternate molt
The prealternate molt, also called prenuptial molt, replaces some feathers for brighter alternate breeding plumage. It precedes the breeding season and is typically less extensive than the prebasic molt.
Some species molt twice annually by undergoing both a prebasic and prealternate molt each year.
How frequently do birds molt?
Molt frequency varies significantly among bird species:
- Some only molt once annually before breeding season.
- Others molt twice annually, before and after breeding season.
- A few species may molt 3-4 times per year, like emperor penguins.
- Birds of prey can molt gradually, replacing just a few feathers at a time over several years.
Here are some examples of molting frequency in different types of birds:
Bird Type | Molts per Year |
---|---|
Chickadees | Once |
Geese | Twice |
Emperor penguins | 3-4 times |
Eagles | Gradual, multi-year |
Stages of the molt process
Molting progresses through several distinct stages:
Premolt
In the days or weeks preceding molt, the bird’s body prepares for the large energy expenditure. The bird may increase appetite and fat reserves during this time.
Molt onset
Molting begins, usually proceeding gradually over weeks or months. Shedding of old feathers and growth of new ones accelerates.
Peak molting
The molt reaches its peak intensity, with the highest rates of feather loss and regrowth. The bird experiences maximum energy usage.
Ending
As the last new feathers grow in, the molt decelerates. Birds may appear disheveled during this time.
Post-molt
With full fresh plumage, the molting process completes. Birds have optimal new feathers.
What happens during the molt?
Molting progresses feather by feather in a generally regular sequence:
- Old feathers are pushed out as pin feathers emerge.
- Blood flow increases to supply nutrients to growing feathers.
- Feathers grow enclosed in a waxy keratinous sheath.
- Feathers emerge from sheaths when fully formed.
- Birds preen new feathers to remove sheath remnants.
The actual shedding and replacement process happens over just 1-2 days per feather. But because the overall body molt involves hundreds of feathers, the entire molting period lasts much longer.
How do birds molt their flight feathers?
Flight feathers on the wings and tail require special molting strategies. Because birds cannot fly without these feathers, they are replaced sequentially to preserve some flight capacity:
- Primary wing feathers molt in a numbered sequence, starting in the middle.
- Secondary wing and tail feathers are replaced in pairs from the inside out.
By molting a few key feathers at a time, birds maintain the ability to fly during the molt. Some birds may still appear flight impaired or weak during heavy molting.
Effects of molting on birds
Molting is energetically expensive for birds and causes many temporary effects:
- Increased appetite – Birds eat more to meet higher energy needs.
- Weakened flight – With missing feathers, flight ability is reduced.
- Greater time spent resting – Birds conserve energy by reducing activity.
- Increased time spent preening – Preen oil helps condition new feathers.
- Heightened vulnerability to predators – Flight impairment makes birds more susceptible to predators.
These effects subside after the molt ends and new plumage is complete. The bird regains peak functional capacities.
How long do different molt stages last?
The duration of specific molt stages can vary from weeks to months depending on the size and species of the bird. Here are some general time spans:
- Premolt period – 1-4 weeks
- Onset of molt – gradual over days/weeks
- Peak molting – 2 weeks to 2 months
- Ending – 1-3 weeks
- Post-molt recovery – variable based on species
The entire process lasts anywhere from 4 weeks to 6 months in most bird species.
Factors impacting molt duration
Several key factors influence the length of time molting takes for a bird:
Age
Younger birds tend to molt faster. Their feathers are less worn and fewer need to be replaced. Older birds molt more feathers and thus require more time.
Health
Poor health, illness, or malnutrition can prolong molts. Healthy robust birds molt more efficiently.
Photoperiod
Increasing or decreasing daylight hours helps stimulate and synchronize molting at certain optimal times of year.
Species
Larger birds with more feathers naturally require longer molt durations. Penguins may molt for 5-6 weeks while small songbirds molt in 4-8 weeks.
Time of year
Molting leading into breeding season is often shorter. Post-breeding molts preparing for winter weather are typically longer.
Extent of molt
A full body molt takes longer than just molting a few specialized feathers.
How long do some common birds molt for?
Here are approximate molting durations for some common bird species:
- Chickadees – 1-2 months
- Robins – 4-8 weeks
- Mallard ducks – 4-5 weeks for males, 6 weeks for females
- Red-winged blackbirds – 2-4 weeks
- Mourning doves – 5-6 weeks
- Blue jays – 2-3 months
- American goldfinches – Early fall for 3-4 weeks
- Sparrows – Varies by species from 4-10 weeks
Molt duration can vary significantly even within a species depending on age, sex, season, and geographic location.
Can molting be dangerous?
Molting is typically a high risk time for birds due to impaired flight from missing feathers. Hazards birds may encounter during molts include:
- Greater vulnerability to predators
- Challenges escaping from threats
- Collisions while fleeing dangerously
- Trouble foraging widely if flight is limited
- Increased energy requirements when food is harder to find
- Greater exposure to elements if insulation decreases
To manage these risks, birds tend to become more reclusive and spend more time resting/hiding. Mortality rates can increase during molting periods.
Do all birds molt?
Nearly all birds molt. A few exceptions include:
- Birds with continuously growing feathers – like cassowaries and emus
- Some birds of prey
- Some tropical species with longer breeding seasons
But the vast majority undergo regular molting cycles throughout their lifetime.
Interesting molting behaviors
Some species exhibit unique molting behaviors and patterns:
- Penguins – Entire colonies molt simultaneously. Birds must fast for 2-5 weeks while flight feathers regrow.
- Waterfowl – Males and females often molt at different times to maintain family groups and offspring care.
- Titmice – May pluck live feathers from other birds to reduce their own molting effort.
- Crossbills – Molt erratically year-round with unpredictable molting durations.
- Tropicbirds – Shed only a portion of flight feathers annually, so they never become flightless.
Molting in domesticated birds
Like wild birds, pet and domesticated fowl regularly molt each year. Average molting periods for domestic birds include:
- Chickens: 4-12 weeks
- Ducks: 4-8 weeks
- Geese: 4-6 weeks
- Pigeons: 6-12 weeks
- Parakeets: 4-10 weeks
- Finches: 2-6 weeks
Providing adequate protein and limiting stress supports healthy molting. Birds may need to be separated if they pluck each other’s feathers.
Conclusion
Molting is a crucial natural process that birds rely on to maintain their plumage in good condition over their lifetime. The process itself places substantial energy demands on birds. Complete molts generally last anywhere from 4 weeks to 6 months for most species. The wide variation reflects differences in body size, extent of molting, age, time of year, environment, and general health. Understanding the molting duration and needs of different birds can help bird lovers support their feathered friends through this taxing annual process.