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The plumage of the Indigo Bunting undergoes dramatic changes between breeding season and fall. In breeding plumage, the male is a stunning, deep, iridescent blue. In fall, the male molts and becomes brown like the female. The female maintains her brown plumage year-round, with some variation in brightness.
The Indigo Bunting (Passerina cyanea) is a small songbird native to North and South America. The breeding male is unmistakable with his brilliant, shimmering blue plumage. However, this plumage is strictly a breeding costume. After the breeding season ends, the male molts and adopts a plumage that closely resembles the brown female. This helps the male stay camouflaged in the fall and winter when he is not trying to attract a mate.
In this article, we will take a closer look at the fall plumage of the male and female Indigo Bunting. We will examine how breeding plumage differs from non-breeding plumage, the molting process, and the purpose behind these seasonal changes.
Male Breeding Plumage
During the breeding season, the male Indigo Bunting is decked out in his most spectacular plumage. His head, throat, back, wings, and tail are a deep blue, often described as indigo, violet, or ultramarine. This coloring results from the physical structure of the feathers, not from pigments. The feathers contain a spongy layer that refracts light. By changing the angle of the feathers, the bunting can alter the wavelength of light reflected, showing off different shades of blue.
When flashing their vibrant plumage, male buntings appear darker on the back and lighter on the breast. This effect helps the blue hues stand out against both dark vegetation behind the bird and lighter blue sky in front of the bird. In optimal lighting conditions, the breast can appear turquoise while the head is a deep royal blue. The wings and tail have black feathers interspersed among the blue.
This dazzling breeding costume helps male Indigo Buntings attract mates and defend territories during the breeding season. The more intensely blue males tend to be preferred by females and hold higher quality territories.
Male Non-breeding Plumage
After breeding season ends, male Indigo Buntings molt into a drab plumage that resembles females and young birds. This non-breeding appearance helps them blend in better in the fall and winter when territorial displays are no longer a priority.
In fall and winter, the male’s head, back, breast, and belly are brown. The brown has a sandy, rusty, or cinnamon tone. The wings and tail are darker brown to blackish. Some blue feathers may persist right after molting but eventually all traces of blue disappear. There is little difference between non-breeding males and females in size, shape, or coloration.
The molting process is gradual, spanning late summer and early fall. Males lose their bright breeding feathers symmetrically and systematically, making the change less abrupt. Juveniles may retain some blue feathers in their first fall before their first breeding season. Males in their second year tend to have more blue than true juveniles.
Female Plumage
Female Indigo Buntings have brown plumage throughout the year. During breeding season, their brown plumage is at its brightest and most colorful. The head, back, rump, and breast are warm cinnamon brown. The belly is paler brown transitioning to whitish. Their wings are blackish-brown with white bars. The tail is blackish-brown with white outer tail feathers. The bill is grayish in females, compared to the all-black bill of males.
After breeding, females molt some of their body feathers, but their appearance does not change substantially. Their non-breeding brown plumage tends to be more drab and muted. The wings and tail feathers receive little to no replacement during molting. Females undergo just one molt per year in late summer, while males have two molts due to their more dramatic seasonal color change.
The drab female plumage provides good camouflage year-round as they incubate eggs, raise young, and forage in vegetation. Drab fall plumage in both sexes reduces risk of predation during the non-breeding season.
Plumage Timeline
Here is a timeline summarizing the plumage cycle of the Indigo Bunting throughout the year:
Spring
– Males transition to brilliant blue breeding plumage with some black in wings and tail
– Females are warm brown with cinnamon tones
Summer
– Males sustain deep blue breeding plumage for courtship and mating
– Females remain brown though possibly brighter than other seasons
Fall
– Males molt blue feathers and replace them with drab brown ones similar to females
– Females molt some body feathers and become more muted brown
Winter
– Males and females nearly indistinguishable in drab brown plumage
Molting Process
To transition between breeding and non-breeding plumages, birds undergo an annual molt. Molting is the process of shedding old worn feathers and growing new ones. Indigo Buntings molt in the late summer and early fall.
Molting happens gradually over several weeks because it is energetically costly to replace many feathers at once. The timing is carefully regulated by hormones to ensure successful completion.
Male Indigo Buntings tend to molt earlier than females, beginning in July or August. Juveniles start molting sooner after leaving the nest. Molting moves systematically across the body – for instance, starting at the head and moving down the back. Symmetrical molting on both sides helps maintain balance and flight ability.
Stress hormones can delay molting, especially for birds recovering from the breeding season. Good food availability helps ensure nutrients for growing new feathers. Some blue feathers may persist through the first fall molt in young males.
Purposes of Molting
Molting serves several important purposes for birds:
– Replace old, worn feathers – Feathers degrade from a year of use and need replacement to maintain flight and insulation.
– Change color – Molting allows seasonal shifts between breeding and non-breeding plumages.
– Reduce parasite load – Shedding feathers removes feather lice and other external parasites.
– Permit maintenance – With feathers dropped, birds can access skin and muscles for maintenance and cleaning.
– Improve insulation – New feathers hold more air and provide better insulation in cold months.
– Reduce wear – Non-breeding plumage protects feathers from degradation during non-mating months.
– Conserve resources – Drab non-breeding plumage uses less energy to produce than bright breeding plumage.
Evolution of Molting
Molting likely originated over 150 million years ago in the common ancestor of all modern birds. Feather molting evolved as a solution to replace damaged feathers and maintain the feather coat.
Later on, seasonal molting adapted through natural selection to serve additional purposes like changing color and improving insulation. In most temperate zone birds today, an annual molt is timed to produce warm insulating plumage for winter.
Tropical birds may have a more continuous molting pattern, less driven by seasonal climate change. Some birds have even lost the ability to molt altogether. But for Indigo Buntings and most North American passerines, one or two molts per year is essential to survival.
Importance of Fall Molting
Molting in fall serves several critical purposes specific to that time of year:
– Allows males to replace bright breeding plumage with camouflaged non-breeding plumage.
– Provides all birds with fresh feathers for optimal insulation through cold months.
– Removes feathers with built up parasite loads after breeding season.
– Gives time for molting completion before migrating south or wintering.
– Allows females to replace heavily used breeding season feathers.
– Reduces conspicuousness during fall migration to avoid predation.
– Saves energy since bill and plumage are less bright for males and less energy intensive to produce.
The timing of fall molting is closely tuned to complete these seasonal tasks. Delayed molting could impair migration, insulation, or camouflage.
Geographic Variation
The Indigo Bunting’s distinctive molt occurs throughout its breeding range in North America. However, some subtle geographic variation exists:
– Western birds have duller blue breeding plumage with more brown than eastern birds. Their non-breeding plumage is also dingier.
– Southern birds tend to retain some blue feathers through winter while northern birds are uniformly brown in winter.
– Tropical resident populations may have a limited prealternate molt before breeding season and lack a complete fall molt.
– Molt timing is earlier for northerly migratory populations so molting finishes before migration.
– Western migratory populations have a more synchronous, rapid molt while eastern birds have a more drawn-out, gradual molt.
Despite these minor variations, the Indigo Bunting’s dramatic molt remains a defining feature throughout its range. The blue to brown transition is integral to the species’ life history.
Comparison to Related Species
The Indigo Bunting is not the only North American songbird to undergo a striking molt. Here is how some related species compare:
Blue Grosbeak
Males have similar blue to brown molt but lack black wing and tail feathers when breeding. Females are cinnamon-brown like Indigo Buntings.
Lazuli Bunting
Very similar pattern but Lazuli’s have more white in their wings during breeding plumage. Males are darker blue than Indigo Buntings.
Painted Bunting
Males have a more dramatic molt from red, green, blue, and yellow breeding plumage to pale green-yellow non-breeding colors. Females always greenish.
Dickcissel
No change as dramatic as Indigo Bunting. Males have yellow shoulder patch when breeding, less distinct when not breeding. Females plain light brown.
American Goldfinch
Also changes from bright yellow breeding plumage to dull brown in winter. But male and female goldfinches have identical plumage.
Conclusion
The fall molt of the Indigo Bunting transforms its appearance from flashy blue breeding costume to camouflaged brown winter coat. This plumage change is integral to the species’ annual cycle across its North American range. Molting allows birds to replace worn feathers, change colors, conserve energy, reduce parasites, and avoid predation at different times of year. The Presidio variety develops along a employee valuation woodland floor and bears a physical resemblance to its mom or dad species, Thuja plicata. It shares the identical fan-like foliage and layered progress behavior. Nonetheless, the foliage is bright inexperienced to yellow-inexperienced in colour compared with the darker inexperienced scale-like leaves of western redcedar.