Embedded Files
Learning how to age gulls is actually pretty straightforward - with patience and practice! Using a scientifically-approved terminology for bird (and gull) molt is a bit of a can of worms - so we aren't using anything too specific here. The goal is to get more comfortable with ageing gulls for what they are (for now) - and at the end there is some "further reading" if you're keen to do a deep dive on bird molt.
Two Year Gulls
Two Year Gulls
Bonaparte's Gull
Little Gull
Black-legged Kittiwake
Ivory Gull
Sabine's Gull
Black-headed Gull
Ross's Gull
Laughing Gull
Franklin's Gull
Three Year Gulls
Three Year Gulls
Ring-billed Gull
-
Black-tailed Gull
Heermann's Gull
Common Gull
Mew (Short-billed) Gull
Western Gull
Four Year Gulls
Four Year Gulls
American Herring Gull
Great Black-backed Gull
Lesser Black-backed Gull
Iceland Gull
Glaucous Gull
California Gull
European Herring Gull
Vega Gull
Slaty-backed Gull
Glaucous-winged Gull
Kelp Gull
Not unlike learning four-letter bird codes, there are general rules (large gulls = 4 year gulls, small gulls = 2 year gulls) and hard rules (Western Gull is actually a 3-year gull?), that require some basic memorization in order to become comfortable with ageing gulls. We'll dive into some unusual/atypical situations later on, but for now - a basic overview of gull plumages:
Two Year Gulls:
Juvenile Plumage
Two Year Gulls:
Juvenile Plumage
Three Year Gulls:
Juvenile Plumage
Three Year Gulls:
Juvenile Plumage
Four Year Gulls:
Juvenile Plumage
Four Year Gulls:
Juvenile Plumage
Regardless of how long it takes for a gull to grow up, they all start by growing in their initial juvenile plumage that we encounter in the field. They're generally dark and (at least initially) crisply patterned. After a period of weeks to several months, almost all will molt into a first winter/first basic/first cycle plumage. The variation on when a bird begins it's molt depends on when it was born, it's health, it's need to migrate, food availability and/or energy requirements (ie how cold it is).
With the first replaced/molted juvenile body feathers, a gull enters it's "First Cycle" (see below). No flight feathers are replaced at this time (primaries, secondaries, tail).
Two Year Gulls:
First Cycle (winter)
Two Year Gulls:
First Cycle (winter)
Many two-year gulls share similar features (such as an "M" pattern on the back) with Laughing and Franklin's being more unique. Black-legged Kittiwake and Ivory Gull may appear no different from their juvenile plumage throughout the first year.
Three Year Gulls:
First Cycle (winter)
Three Year Gulls:
First Cycle (winter)
Most three-year gulls replace a number of body feathers in the fall/early-winter of their first year - resulting in a notable change from their juvenile appearance. Mantle (back) feathers are sometimes, but not always, quite adult-like.
Four Year Gulls:
First Cycle (winter)
Four Year Gulls:
First Cycle (winter)
While some four year gulls will also replace a number of body feathers in their first fall/winter, they are generally less contrasting. Some (often northern nesters) replace little to no feathers and/or they are very hard to notice in the field.
Many gulls may once again start replacing body feathers in the spring as conditions improve. The hard-line shift to their Second Cycle involves the molt of the major feather tracts, specifically the inner primaries, which appear as a "gap" when the old juvenile feather is dropped.
Two Year Gulls:
Second Cycle (summer)
Two Year Gulls:
Second Cycle (summer)
Note the adult-like incoming primaries. Our young Bonaparte's Gull is in the process of molting in an adult-like winter plumage, meaning by the end of the season we won't (really) be able to age them anymore. Due to the fact they're growing up, some birds (like our photo example) get adult-like hormones which can bring in adult-like feathers (or bare part colouration). Most would not show show much black on the head from their early-spring molt. These head feathers will change again before winter (see below).
Three Year Gulls:
Second Cycle (summer)
Three Year Gulls:
Second Cycle (summer)
More adult-like feathers are coming in on our young Ring-billed Gull. Their proximity to adulthood sometimes causes some enhanced bare part colouration during the spring (i.e., "breeding" season). Many would get a pretty white head as well. The hallmark of a three year gull is that they get quite adult-like through the summer, but are still fairly distinctive compared to a true adult by the time winter comes (see below).
Four Year Gulls:
Second Cycle (summer)
Four Year Gulls:
Second Cycle (summer)
Our young Lesser Black-backed Gull is a bit of a mess by mid-summer, being part way through replacing all their feathers. In four year gulls, only a few are adult-like, generally on the mantle with some birds also showing some adult like coverts. This is unlike our two and three year gulls to the left, which are becoming quite adult-like. Check out the end result of this summer molt below.
Summer is the period of molt and change for most gulls. By early winter, most have acquired their full second-cycle plumage. We've split out how the molting, ratty, and intermediate birds (above) can look compared to their final product (below).
Two Year Gulls:
Second Cycle (winter)
Two Year Gulls:
Second Cycle (winter)
Rarely, we may see some atypical dark markings in the outer primaries that could help us notice our Bonaparte's Gull is just reaching adulthood, but most won't be noticeable in the crowd. They will also obtain breeding plumage in spring, before any primary molt occurs. The inner primaries won't be molted until their breeding duties are complete, likely mid- to late summer - which is much delayed compared to the non-adult birds.
Interestingly, some of our "two year" gulls - like Little Gull - show more distinctive "second cycle" plumages than you might think. We'll delve into ageing each species, in detail, once our four-year gulls mature.
Three Year Gulls:
Second Cycle (winter)
Three Year Gulls:
Second Cycle (winter)
Our Ring-billed Gull is - almost - all grown up! Perhaps most crucially is their lack of white primary spots and primary mirrors. But also the black tail markings, and the black tertial markings, and the wing coverts are a bit messy, and the head/breast streaking is quite extensive, and the eye isn't quite pale yet. Each Ring-billed Gull will vary in many of these qualities, but virtually all are readily noticed as "second winter" birds.
Four Year Gulls:
Second Cycle (winter)
Four Year Gulls:
Second Cycle (winter)
Note how "immature" the vast majority of these new feathers are. Legs, eye and bill have made limited progress. The key elements here are:
The adult-like feathers are only on the mantle, and sometimes as wing coverts.
The primaries do not show adult-like feathers.
They've lost the crisp/fresh and more uniformed look of the juvenile / 1st winter birds.
The amount of individual variation is increasing at this age, but those key features should pick out a second-winter bird with confidence.
Similar to before, the next "cycle" begins with the first dropped inner primary. This is where our gulls really start to deviate, as our Bonaparte's Gull has completed the process of maturing - in two years! We'll skip the messy/intermediate "summer" look and just focus on the end product for our remaining birds.
Three Year Gulls:
Third Cycle (winter)
Three Year Gulls:
Third Cycle (winter)
It's all adulthood from here on out. Note the primaries - big white spots and primary mirrors. The less reliable and variable signs of immaturity are also gone. Before the next cycle begins, our Ring-billed Gull will molt some body feathers and obtain "breeding" plumage.
Then the cycle from breeding to non-breeding plumage plays out annually thereafter. It's just noticeably later in the year once they become adults, as our gulls delay their annual full-body molt until after their nesting obligations are over!
Four Year Gulls:
Third Cycle (winter)
Four Year Gulls:
Third Cycle (winter)
A switch gets flipped between second and third cycle, where our four-year gulls suddenly look more adult-like than juvenile-like. Individual variation is extreme, but the key feature here is the adult-like inner primaries, slaty gray (i.e., adult like) with nice white tips. Our bird is still molting the last few primaries, but it's entirely possible that the new P10 will have a small white mirror at the tip.
And then there was one. Our four-year Lesser Black-backed Gull has one more summer of molting before reaching its "adulthood". Again, we'll skip the messy summer look and jump to the final product.
Four Year Gulls:
Fourth Cycle (winter)
Four Year Gulls:
Fourth Cycle (winter)
As with our other gulls, there may be some subtle hints that our Lesser Black-backed Gull has just reached its fourth year - but for the most part you won't be able to tell it apart from the other "adults" in the group. The wings and tail are notably crisp.
As with our 2 and 3 year gulls, a spring body/head molt with usher in "breeding" plumage, and the partial breeding / complete winter molts will continue thereafter.
The gull research website has a great month-by-month photo salon of banded LBBG showing this four-year progression here!
Juvenile to First Winter?
We've used the terms "juvenile" and "first winter" on this page - and it's one of the more interesting elements about aging gulls, largely due to the variation observed, such as:
Birds which briefly keep juvenile plumage before beginning to molt in some "first winter" feathers.
These are usually southern or early nesters and have more extensive first winter molt.
Some small species (like Bonaparte's Gulls, Little Gulls, etc.) may also have brown or blackish feather tips that soon wear off, revealing an more distinct white feather appearance below.
Birds which may hold onto juvenile plumage for most or all of their "first winter".
These are usually northern or late nesters.
Birds which molt in distinctive "first winter" feathers.
Most of the 2-year gulls, and some of the 3-year gulls.
Birds which molt in un-distinctive "first winter" feathers.
Some of the 3-year gulls and most of the 4-year gulls.
We've pulled some specific examples of these situations to show below, with the goal of making it easier to recognize juvenile vs. 1st winter feathers.
"First Year" vs "Second Year" Primary Feather Shape in four-year Gulls
A helpful and reasonably reliable way to separate similar-looking first year and second year "four year" gulls.
Beware that single photos can be deceiving, but also that some individuals still try to break the rules.
"Second Year" vs "Third Year" Primary Patterns in four-year Gulls
A more detailed look at how primary pattern can be used to separate similar looking second year and third year "four year" gulls.
The "Five Year" Gull Problem
While all of these tricks and features are used to age gulls, it's worth considering we don't actually know (at least not 100% for sure) that our gulls are their apparent age without a band on their leg to confirm.
Some individuals from four-year gull species can appear delayed in their second year and/or third year plumages... Sometimes a bird may be delayed by injury or illness, but it often involves a northerly nesting species. An example of this "problem" is shown below:
Second Year Lesser Black-backed Gull (Nov)
Many LBBG show limited advancement (e.g., adult-like gray feathers) in their second year.
Third Year Lesser Black-backed Gull (Nov)
It's also not uncommon to find rather "delayed" third-year LBBG. Note the lack of primary mirrors and extensive "immature" markings... But there are white tips on the inner primaries (i.e., a strong third year feature). This advancement into third-year plumage would also align with the delayed second year birds as noted above.
Fourth? Year Lesser Black-backed Gull (Nov)
Conventional gull ageing suggests this adult-like LBBG, with signs of immaturity such as black on the bill or dark covert, primary, secondary or tail markings, would indicate "third winter" plumage. However, note the outer two old primaries from the previous year have a white primary mirror, indicating it's likely at least four years old (indicating 5+ years to mature).
If your goal is strictly identification, there probably is no need to worry about potential for delayed fourth-year plumages, as the ID features for a given species are unlikely to change. With that said, it's worthwhile to keep in mind if you enjoy gull study and trying understanding exactly what you're looking at. Check out the Gull ID page for more on five-year gulls.
Reversed Seasons in Adult Gulls
Rarely you may encounter an adult gull that is in winter plumage in the spring/summer or an adult gull in breeding plumage during the winter, like this adult Bonaparte's Gull from Ohio in early January!
These are fun anomalous individuals, and their reversed molt is usually not important for identification - beyond recognizing the switch has happened!
Articles on Molt:
Plumage and Molt Terminology - Ontario Birds - 2000
A Comment on Molt and Plumage Terminology: Implications from the Western Gull - Western Birds - 2000
The First Basic Problem: A Review of Molt and Plumage Homologies - The Condor - 2003
Searching for consensus in molt terminology 11 years after Howell et al.'s "first basic problem" - The Auk - 2014
Use of ‘‘definitive’’ and other terms in molt nomenclature: A response to Wolfe et al. (2014) - The Auk - 2015
Species by Species Reference
Now that we've got the gist - some notes and examples by species are provided below:
Black-legged Kittiwake - BLKI
Two year gull. Nuance includes:
Little field difference between "juvenile" and "first winter" plumages.
Arguably has a distinct "second winter" plumage, with weaker contrast in the primary pattern, plus additional dark "immature" markings.
Juvenile / First Winter. Strong black "M" pattern with dark hindcollar. Dark bill and legs. First spring obtains yellow on the bill and a more patchy plumage overall.
Second Winter. Note adult-like plumage, but weaker wingtip pattern (less white between black tip and gray wings). Black extends up P10, with black flecks in some coverts.
Adult. Both winter and breeding plumages shown. No signs of immaturity, stronger wing pattern. Breeding adults with brightest bill. Winter adult with dusky nape markings.
Ivory Gull - IVGU
Two year gull. Nuance includes:
Perhaps no first-winter molt - retains juvenile plumage.
Juvenile. Brilliant white with black markings which follow a similar pattern between individuals but vary in intensity.
Adult. Whiter than snow. Beware pure white leucistic gulls of other species. Very lightly marked juvenile may look pure white at a distance. Breeding adult gets brighter bill and eyering.
Sabine's Gull - SAGU
Two year gull. Nuance includes:
Adults in fall (locally) are usually in full breeding plumage, with molt likely beginning once the reach the ocean or their ideal staging grounds.
Juvenile. Note extensive brown. At great distance, brown may not be discernable and head may appear dark like adult breeding.
First Winter. Very rare locally. Brown plumage gradually replaced with gray feathers.
Adult. Gray back. Breeding adult with full black head. Very rare to see adult-like non-breeding plumage locally.
Bonaparte's Gull - BOGU
Two year gull. Nuance includes:
Tiered migration, with birds arriving locally and staying for a few months to molt, before moving further north to breed or south during our coldest weather.
A cryptic "second winter" plumage may be detected with careful study / select individuals (see photos in the "reference by month" page).
Juvenile. Black "M" pattern less obvious below brown-washed juvenile feathers.
First Winter / Spring. Brown feathers molted and also perhaps wears off any retained feathers. "M" becomes more obvious. First spring gets variable black head markings.
Adult. Crisp with distinct wing pattern. Breeding adult obtains black head with white eye arcs.
Black-headed Gull - BHGU
Two year gull. Nuance includes:
Juvenile plumage perhaps unrecorded locally. Adults more regular than younger birds.
Unclear if individuals ever show a recognisable "second year" plumage.
First Winter / Spring. Orange-pink to red bill and/or legs. "M" pattern not quite as prominent due to dark secondaries. Rarer locally than adult. Obtains variable dark brown hood in spring.
Adult. Crisp plumage overall with red bill and legs. Breeding adult obtains brown-black hood with white eye arcs.
Little Gull - LIGU
Two year gull. Nuance includes:
Not actually a two year gull, with a distinct second-year plumage.
Tiered migration locally. Numbers fluctuate annually at some locations.
Juvenile. Distinct, very dark juvenile plumage rare but regular in our area. Birds tend to begin molt into first winter plumage soon after arriving locally.
First Winter / Spring. Many dark mantle feathers replaced, revealing very strong M pattern. Spring birds can obtain variably dark head.
Second Winter / Spring. Many are distinct vs. adult due to paler gray (or patchy) underwing. Some have dark markings on upperside of outer primaries visible in flight or perched. Most obtain full black head in spring.
Adult. Crisp markings. Dark underwing distinctive. No black markings on upperside of primaries. Breeding plumaged adult with extensive black hood with no white markings around eye.
Ross's Gull - ROGU
Two year gull. Nuance includes:
Super rare. Adults may be more frequent than first winter. Juvenile plumage unrecorded.
No local evidence of a detectable "second winter" plumage.
First Winter / Spring. Bold black "M". Plumage recalls Little Gull but longer, pointed structure w/ black tips to inner primaries. Black extends down inner primary tips. All ages has variable pink wash.
Adult. Clean markings. Silvery-gray underwing - more smooth than second winter Little Gull. May retain faint neck collar.
Laughing Gull - LAGU
Two year gull. Nuance includes:
Reasonably identifiable second year plumage (i.e., not really a two year gull?). Although some may be indistinguishable from adults.
Juvenile. Brownish overall. Uniform mantle feathers, crisp and pale edged.
First Winter / Spring. Mantle and perhaps some coverts molted in gray. Stays pretty ratty into their first spring.
Second Winter / Spring. Similar to adult but with signs of immaturity in wing coverts (dark markings) and primaries (reduced white). Obtains dark head in spring (breeding plumage) but bare parts usually less red than full adult.
Adult. More sharply defined plumage, lacking messy dark wing markings. More white on primaries. Legs and bill become brighter red in spring. Black hood in spring complete with sharply defined eye arcs.
Franklin's Gull - FRGU
Two year gull. Nuance includes:
Our only gull with two complete molts annually (i.e., including flight feathers). This leads to some unique / fresh spring plumages - and sometimes some particularly unusual individuals.
Juvenile. Rare locally. Brownish overall with fresh mantle and covert feathers.
First Winter. Similar to other two-year gulls, new adult-like gray feathers come in on the mantle and many brownish washed feathers becoming white.
First Spring. Due to the complete winter molt, our year-old Franklin's Gulls arrive with a remarkably fresh plumage compared to other similar species - looking similar to winter plumaged adults.
Adult. Fresh overall. Strong black, white & gray contrast in the wings. Full hood, eye arcs and bright bills in breeding plumage.
Some 2nd year Franklin's Gulls may be noticed by subtle dark covert markings - becoming more obvious in spring if their hoods are incomplete. Smaller white primary spots and/or heavier black markings on the head could be reason to investigate a open wing carefully (in fall) to confirm age.
Black-tailed Gull - BTGU
Three year gull. Nuance includes:
Very rare locally. Unlikely to occur as a juvenile or first winter.
No primary mirrors as an adult! Plus that unique black tail.
First Winter. Unique contrasting dark brown plumage with variable light areas. Always strong bill contrast.
Second Winter. A messy intermediate plumage with variable amount of adult-like gray mantle feathers and coverts.
Adult. Cleaner dark mantle, but atypical GISS with lack of primary mirrors. Unique bill pattern. Bill and legs turn brighter yellow in spring- summer.
Heermann's Gull - HEEG
Three year gull. Unique plumage aspects at all ages. Nuance includes:
Very rare locally. Individuals are often tracked from one location to the next as they wander.
Juvenile plumage generally not expected; however, there is a remarkable July record from Michigan of a fresh juvenile.
First Winter. Very dark overall with black legs. Bill pattern fairly unique compared to other local gulls. Beware dark stained or abberrant gulls of other species.
Second Winter. Similar to a messy adult with patchy feathers, dusky head well into spring. Orange-ish bill becomes more evident with time. Some plumage abnormalities in common species can even mirror adult-like plumages of Heermann's Gull.
Adult. Similar to 2nd winter but clean markings overall with white trailing edge to secondaries. Head becomes bright white early in late winter. Bill becomes brighter and red in spring.
Common Gull - COGU
Three year gull. Nuance includes:
Very rare. Juvenile / 1st winter unlikely to occur locally.
Three subspecies, with the European population noticeably different in plumage and structure than the east Asian Kamchatka population. Basic ageing criteria still apply to each subspecies.
Juvenile / First Winter. Plumages similar to Mew and Ring-billed.
Second Winter. Large primary mirrors similar to Mew Gull. Variable signs of immaturity on an adult-like bird.
Adult. Clean markings. Varible features and mantle shade depending on subspecies.
Mew (Short-billed) Gull - MEGU / SBIG
Three year gull. Nuance includes:
Very rare locally.
Juvenile. Far nothern nesters may be the source of local records, as they sometimes arrive late in retained juvenile plumage.
First Winter. Highly variable. Can be similar to Ring-billed with gray mantle, but some birds fade and give initial in-flight impression of Thayer's Gull.
Second Winter. Frequently/always with notable primary mirrors. Has signs of immaturity on an otherwise adult-like bird.
Adult. Crisp markings. Adult averages heavy head streaking down nape and onto breast in winter.
Ring-billed Gull - RBGU
Three year gull. Nuance includes:
Exceptional variability in first winter plumage (perhaps more than any other local gull species?).
Juvenile. Highly variable in all aspects. Crisp markings. Local nesting birds usually molting by late August. Northern nesters can arrive in juvenile plumage well into fall.
First Winter / Spring. Variable amounts of adult-like gray mantle feathers on most birds. Bill becomes pink with a black tip.
Second Winter. Adult-like birds with highly variable signs of immaturity such as dark on tail, primary coverts, small or missing primary mirrors, paler and/or variable bare part colours.
Adult. Crisp markings. Defined primary mirrors and white primary tips. Legs and bill yellow. Black bill ring clearly defined.
Western Gull - WEGU
Three year gull. Nuance includes:
No Great Lakes records, but could someday occur. Juvenile plumage very unlikely.
May often have detectable "third winter" plumage with subtle marks of immaturity in the outer wing coverts and bill pattern.
First Winter. Perhaps unlikely to occur locally. Overall patterend brownish/dark - similar to other large gulls.
Second Winter. Usually only one year of immaturity with this species. Unclear how vagrancy could alter development and plumage.
Adult. Crisp markings, clear P10 primary mirror, broad clean white tertial skirt. Little to no head streaking in winter.
California Gull - CAGU
Four year gull. Nuance includes:
Juvenile plumage unlikely to occur locally, but not impossible.
"First year" can obtain some adult-like mantle feathers, unlike many other four-year gull species.
Third year usually with subtle signs of immaturity.
First Winter / Spring. Variable gray mantle feathers can molt in. Usually gets pink bill with small black tip during winter.
Second Winter. Similar to other four-year gulls, with gray mantle feathers, but no adult-like features in the wings. Legs variable from pink to gray to blue.
Third Winter. Similar to other four-year gulls. An adult-like bird with variable signs of immaturity such as black on tail, wing coverts, etc.
Adult. Crisp markings. Dark eye. Yellow legs and bill. Darker-mantled californicus subspecies very rare locally.
American Herring Gull - AHGU
Four year gull. Nuance includes:
Distinct "populations" seem to exist locally. Check out the gull identification page for more details on the extensive plumage variation that exists between them. Examples of our local "Great Lakes" breeding birds are used below.
Molt progression for European Herring Gull (EHGU) and Vega Gull (VEGU) is similar.
Juvenile. Fresh overall. Dark-centred mantle feathers distinctive of juvenile. Frequently with mostly or all black bill.
First Winter. New mantle feathers lacking dark-centres. Bill starts to turn pink at the base but highly variable. More worn and contrasting look than juvenile.
Second Winter. Often with some adult-like gray mantle feathers. Often with eye paler than first year. Highly variable. Wingtips lack adult-like features.
Third Winter. An adult-like bird with variable signs of immaturity such as black on coverts or tail. Eye frequently pale now.
Adult. Crisp markings. White tail. Clearly defined primary pattern. Usually no remaining signs of immaturity.
Iceland Gull - ICGU / THGU
Four year gull. Nuance includes:
Hard (to impossible) to note differences between juvenile and first winter plumage. Due to their northern origin, they are less likely to have "first winter" feathers come in during the fall/winter.
Second winter may show hints (Kumlien's) to obvious (Thayer's) primary mirror patterns, but not always.
Criteria other than primary & covert pattern may be required to age very pale / white-winged Iceland Gulls.
Silly variation between Iceland Gull "subspecies" makes feature-based ageing somewhat variable; however, the underlying criteria of four-year gull development generally applies to all birds.
See the Gull ID page for more information on "Iceland" vs. "Kumlien's" vs. "Thayer's" ID.
Juvenile / First Winter. May not molt into first winter, or new feathers may not be noticable. Highly variable.
Second Winter. Usually with some adult-like gray mantle feathers. Eye may start getting pale. Bill may be more yellowish-pink at base. Some show pale primary-mirror like spot.
Third Winter. More adult-like overall. Primary pattern slightly less defined in "white-winged" gulls. Variable signs of immaturity.
Adult. All with crisp markings lacking signs of immaturity. Extreme variation among the "subspecies".
Lesser Black-backed Gull - LBBG
Four year gull. Nuance includes:
Signs of immaturity (dark coverts, dark bill markings) may linger well into fourth, fifth, sixth (etc) years. Meaning the "four year" gull term may not be accurate. It's unclear if all birds take several years to mature, or if there are "North American" LBBG which can (and do) mature in 4 years.
Juvenile. Perhaps the most distinctive juvenile plumage with blackish mantle feathers edged in white. Crisp overall.
First Winter / Spring. Gets more worn and contrasting. Loses many/all dark centered mantle feathers. Variation increases.
Second Winter. Almost always with some adult-gray mantle feathers. Contrast increases, markings less uniform, tail pattern variable. Primaries without adult-like features.
Third Winter. Much more adult-gray feathering. Legs usually becoming more yellow. Underside more white. Some potential for "delayed" third year and fourth-year plumages (see below for more).
Adult. Crisp markings. Clear primary mirror(s). Legs almost always yellow Bill pattern more clearly defined. White tail.
Slaty-backed Gull - SBAG
Four year gull. Nuance includes:
Juvenile / first winter unlikely to occur locally - yet either could occur if "more local" breeding begins.
Possibly takes some individuals more than four years to mature.
Glaucous-winged Gull - GWGU
Four year gull. Nuance includes:
Pure northern birds are arguably five year gulls, with delayed development in 2nd and 3rd winters, leading to recognizable fourth winter plumages in-range. More southern nesters may follow a more expected four-year plumage development.
Rampant in-range hybridization with a 3-year gull (Western) and 4 year gulls (Herring, Glaucous) likely clouds ideal ageing features at times.
Very rare locally.
Juvenile / First Winter. Uniform messy plumage, overall low contrast. Bill usually entirely dark.
Second Winter. Usually at least some gray mantle feathers, bill starts to turn pale. No adult-like primary feathers. Still low contrast but more patchy appearance.
Third Winter. Bill increasingly paler. More gray in mantle. Primaries starting to show underlying adult-like pattern.
Adult. Uniform gray above, mostly or entirely lacking immature markings on coverts and tail. Bill mostly yellow.
Glaucous Gull - GLGU
Four year gull. Nuance includes:
Little to no visible differences between juvenile and first winter.
Advanced looking near-adult birds may be fourth winters or older.
Juvenile / First Winter. Uniform pale, often crispy patterned. Pale bill with dark tip. Eye always dark. May retain juvenile plumage all winter and/or first cycle feathers are not noticeable.
Second Winter. Uniform pale to white; however, usually lacks crisp patterning in first winter. Black bill tip slightly less extensive and clean cut. Often with pale eye.
Third Winter. Gray mantle feathers now becoming evident. Pink on bill fading, sometimes pinkish-yellow.
Adult. Now uniform gray above. Adult-like yellow bill with red gonydeal spot.
Great Black-backed Gull - GBBG
Four year gull. Nuance includes:
Can sometimes show a contrasting primary mirror like feature in 2nd winter.
Brown "immature" feathers on mantle, in third winter, may give the field-impression of a paler mantle overall than full adults.
Juvenile. Very crisp overall. Dark bill. Mantle feathers have uniform dark centres with variably wide pale fringes.
First Winter. Mantle feathers replaced with "anchor" patterned first winter feathers. Bill may get paler with some pink visible.
Second Winter. Usually some dark adult-like feathers visible. More variably patchy appearance / less crisp overall. Rare but regular with small white mirror spot on P10, unlike other large gulls.
Third Winter. Now closer to adult-like plumage than first winter. Highly variable bill pattern, usually with lots of pink or yellow. Adult-like primary pattern evident with large mirrors and apical spots.
Adult. Uniform dark above. Adult-like primaries with white tip to P10 and large P9 mirror. Yellow bill with red/black gonydeal spot.
Kelp Gull - KEGU
Three year gull. Nuance includes:
Very rare locally. Only one record locally of a non-adult bird. Multi-year clusters of records could involve one wandering individual.
First calendar year birds are less likely, due to the distances involved between the Great Lakes and breeding locations.
Could in theory have their molt timing on a southern hemisphere cycle (reversed to ours).
"First Year" likely to be ratty or perhaps close to second cycle if occurring locally.
"Second Year" with extensive blackish mantle feathers. May have small or no primary mirror.
Adult. Jet black mantle with clean cut primary pattern (incl. small P10 mirror. Unclear if a 3rd cycle is possibly/subtly detectable.
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