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What's in a name? Nomenclature for colour aberrations in birds reviewed by Hein van Grouw acts as the basis for classifying the primary aberrant plumages shared on this page. We've done our best to sort the birds presented below, however there are likely mistakes. If you have any thoughts on how to improve this section, including classifications - please let us know!
Some common species have many well documented examples of abnormal plumages. To help show how pigmentation can alter appearance, we've made a species-specific page for American Robin here!
Leucism / Leucistic Birds
Patterned:
Black-capped Chickadee from Ontario in 2022.
Patchy:
Killdeer from Ontario in Aug 2023.
Eastern Kingbird, photos and text from Ontario in 2018.
Swainson's Thrush from Ontario in 2012. (grizzle?)
Black-throated Blue Warbler from Michigan in Sep 2006. (grizzle?)
White:
Green Heron from Illinois in 2015.
Red-tailed Hawk from Ontario in 2020, Michigan in 2019. Difficult to rule out advanced progressive greying.
Tree Swallow from Ontario in 2014.
Black-capped Chickadee from Ontario in 2020. Difficult to rule out advanced progressive greying.
Progressive Greying
Great Blue Heron from New York in 2006.
Killdeer from Ontario in 2023.
Semipalmated Plover from Ontario in 2018.
Red-tailed Hawk from Ontario in 2023.
Turkey Vulture from Ontario in 2022.
Downy Woodpecker from Minnesota in 2018.
Black-capped Chickadee from Ontario in 2022.
Yellow-rumped Warbler from Pennsylvania in 2020.
Nelson's Sparrow from Ontario in 2023.
Song Sparrow from Ontario in 2020.
Common Grackle from Michigan in 2023.
Rusty Blackbird from Ontario in 2022.
Albino
Northern Rough-winged Swallow from New York in 2022.
Barn Swallow from Ontario in 2024.
Ruby-throated Hummingbird from Ontario in 2023.
Blue Jay from Ontario in 2014.
American Robin from Ontario in 2020, Ohio in 2022.
House Sparrow from Ontario in 2018.
Brown / Aeumelanism
Northern Shoveler from Michigan in 2020.
Red-breasted Merganser from Ontario in 2023.
Ring-billed Gull from Ontario in 2022.
Herring Gull from Ohio in 2018.
Dunlin from Ontario in Jul 2014.
Double-crested Cormorant from Ontario in 2018
Bald Eagle from Pennsylvania in 2022.
Great Gray Owl from Minnesota in 2004.
Mourning Dove from Wisconsin in 2022.
Common Raven from Quebec in 2023.
Ruby-throated Hummingbird from Minnesota in 2022.
Black-capped Chickadee from Ontario in 2021.
Red-breasted Nuthatch from Ontario in 2014.
Yellow-rumped Warbler from Ontario in 2022.
Downy Woodpecker from Ontario in 2020.
Hairy Woodpecker from Ontario in 2020. Molt has likely made for a more contrasting appearance.
Brown-headed Cowbird from Minnesota in 2018.
Red-winged Blackbird from Ontario in 2023.
Ino
Wood Duck from Ontario in 2017. Possibly captive origin.
House Finch from Wisconsin in 2020. Possibly just "brown".
Dilution
American Robin from Ontario in 2023 lacking the reddish pigments.
Common Grackle from Ohio in 2023 with a dark head but pale body.
Pastel / Hypomelanism
Redhead from Ontario in Jan 2025.
Green Heron from Ontario in Jul 2025.
Barn Swallow from Pennsylvania in 2016.
Black-capped Chickadee from Ontario in Dec 2023.
Cedar Waxwing from Minnesota in 2023.
Bohemian Waxwing from Michigan in 2022.
Swainson's Thrush from Ontario in 2013.
Yellow-rumped Warbler from Ohio in 2011.
Swamp Sparrow from Illinois in 2022.
White-throated Sparrow from Minnesota in 2019.
Dark-eyed Junco from Minnesota in 2022.
Northern Cardinal from Indiana in 2021.
Isabel / Aphaeomelanism
Pileated Woodpecker from Iowa in 2015.
Northern Flicker from Ontario in 2020.
American Robin from Ontario in 2023, Ohio in 2023, Michigan in 2019.
Northern Waterthrush from Ontario in 2020.
Evening Grosbeak from New York in 2023.
Northern Cardinal from Ontario in 2019.
Melanism / Hypermelanism
Dunlin from Ontario in November 2023.
Ring-billed Gull from Ohio in December 2022.
Herring Gull from Illinois in February 2021.
Great Gray Owl from Minnesota in 2004.
Tree Swallow from Ontario in 2016.
Downy Woodpecker from Ontario in 2024.
House Sparrow from Ontario in Jan 2024. Confirmed similar plumage ~1 year apart in 2025!
Black-and-white Warbler from Ontario in May 2016.
Evening Grosbeak from Ontario in 2023. Possibly dilution of the yellow pigment.
Evening Grosbeak from Ontario in Feb 2024.
Dark-eyed Junco from Michigan in Apr 2013.
Extra Red:
Rose-breasted Grosbeak (male) from Ontario in 2004
Fox Sparrow, written account of an atypically reddish bird from Ontario in 1997.
Extra Blue:
Belted Kingfisher from Ohio in 2023, Minnesota in 2023.
Extra Yellow:
Yellow-rumped Warbler from Ontario in 2011.
Evening Grosbeak candidate from Ontario in Mar 2024.
Complex / Multiple Aberrant Types
Rarely, some individual birds may show multiple plumage abnormalities with atypically light/leucistic and dark/melanistic plumage features.
Herring Gull from Ontario in Dec 2020.
Ring-billed Gull from Ontario in Jun 2022.
Further Aberrant to be Reviewed / Updated:
Heritable Greying? :
Red-shouldered Hawk from Ohio in 2021. Unclear if this or an atypical dilution.
Red-tailed Hawk from Ontario in 2024.
Chestnut-sided Warbler from Minnesota in 2023.
Scarlet Tanager from Ontario in 2023.
Head & Bare Parts Specific Leucism?
Common Grackle from Ontario in 2024.
Blue Jay from Ontario in 2019.
Yellow-rumped Warbler from Ontario in 2024.
Common Redpoll from Ontario in 2013.
Northern Cardinal from Indiana in Jan 2025.
Unknown
Ring-billed Gull from Ontario in Aug 2024.
Diet-based Aberrants
Ring-billed Gulls with pink wash. A page showing multiple birds from Ontario in 2016.
Baltimore Oriole, When Orioles Turn Red. Notes on a presumed diet-altered plumage from Ontario.
Cedar Waxwing with Orange/Red tail tip from Ontario in 2022, Ontario in 2023, and Ontario in 2017. See further reading (abstract) here.
Northern Flicker with orange-tinge to select flight feathers from Ontario in 2021.
Dilute Red
House Finch from Ontario in 2022, Ohio in Feb 2025.
Rose-breasted Grosbeak from Ontario in 2019.
Scarlet Tanager from Ontario in 2018, Ontario in 2019, Ontario in May 2024.
Staining
Brown
Downy Woodpecker from Michigan in 2021. Perhaps more common in woodpeckers due to their use of rotting wood.
Gray
Ring-billed Gull from Ontario in 2006. Local gulls may get stained from nesting or roosting in industrial facilities around the Great Lakes.
Yellow
Ring-billed Gull from Ontario in 2006.
Red
Ring-billed Gull from Illinois in 2019. See a note here on local pink/red staining in local gulls and terns.
Snowy Owl from Michigan in Jan 2025. A well publicized individual, possibly hit with airplane deicing fluid.
Snowy Owl from Michigan in Apr 2024. A more "normal" staining event, perhaps similar to the gulls noted above, which may be due to industrial plants along the Great Lakes.
Pink
Herring Gull from Ohio in 2019. Ring-billed Gull from Ohio in 2024.
Further gull staining may be from exposure to garbage, compost or dyes while foraging at landfills.
Oiled
Great Blue Heron from Ohio in 2013.
Ring-billed Gull from Indiana in 2021.
Further Aberrants
Additional atypical individuals you may encounter include:
Gynandromorph
A gynandromorph is an organism that contains both male and female characteristics and is most frequently recognized in birds that have strong sexual dimorphism.
Here's an example of a bi-lateral gynandromorphic (left side female, right side male) Evening Grosbeak from Ontario in Feb 2024. An article was linked which discusses a similar bird collected in Minnesota in Jan 1982.
Further examples include:
Northern Cardinals from Ohio Jan in 2024, Illinois in Apr 2020.
Rose-breasted Grosbeak from Pennsylvania in Sep 2020.
Spontaneous Sex Reversal
Sexually-dimorphic birds can sometimes go though spontaneous sex, which can cause females to exhibit male plumage, and vice versa (phenotypic feminization or masculinization). This may be most commonly encountered in the region among female Mallards with variable male plumage, but usually retaining a female-like bill pattern. Some examples include:
Partial plumage change from Ontario in Dec 2023
Extensive plumage change from Ontario in Jan 2024
Further examples: Canvasback from Ontario in Feb 2025.
Recognizing feminization in males may be more challenging due to their most subtle plumage, raising confusion with possible hybrids (e.g., ABDUxMALL), or atypical molt such as atypically retained eclipse or juvenile (i.e., more female-like) feathers. Some examples include:
An interesting candidate from Ontario in Jan 2018. Note the atypical tail curl and mature adult bill pattern.
Seasonal Plumage Reversal
TBA
Blackpoll Warbler from Michigan in Oct 2024 showing extensive alternate plumage.
Bonaparte's Gull showing alternate/breeding plumage from Ontario in Nov 2024. Another example from Ontario in Dec 2005 notes that the bare part colouration has also entered a bright breeding condition, indicating that the birds overall hormone levels have likely reversed.
Structural Anomalies
Trauma Fault Barring
During molt a significant struggle such as hunger, illness or injury can affect the colour and structure of newly grown feathers. It is most recognizable in young birds, where all feathers are growing in at the same time, leading to bold/extensive "patterns". Older birds may only have isolated feathers affected due to the prolonged nature of feather replacement. Most examples involve gulls:
A selection of Herring Gulls from Ontario in Dec 2012, Ontario in Aug 2010,
Bill Growth Anomalies
Injury, illness, or other factors may lead to anomalous growth of the bill or other body parts. General injuries or deformations have been excluded from this page, beyond a few notable examples below.
Great Black-backed Gull from Ontario in Jul 2007 - with an atypically long bill and with an exceptional "hooked" appearance.
Other
Feather integrity and structure may be influenced by other unknown factors. Some "other" notable birds are presented below.
Dark-eyed Junco from Indiana in Apr 2025 - with unusually fanned / curled tail feathers.
Aberrant or "Wrong" Songs
While much individual variation exists within the songs of a given bird species, sometimes individuals may sing in ways unlike anything expected for their species, incorporate unusual elements of other sounds or species songs into their own, or even sing the songs of a different bird species altogether. See:
A Common Yellowthroat from Ontario in Jun 2024 singing a Prothonotary Warbler song (video).
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