Franklin's Gull vs. Bonaparte's Gull: A Prairie Field Guide

The quickest way to separate Franklin's Gull from Bonaparte's Gull is to watch the outer wing. Franklin's Gull has black wingtips on a dark gray wing, set off by a white band and small white tips. Bonaparte's Gull shows a bright white wedge along the front edge of the outer wing with a thin black trailing edge. A few other clues help: Franklin's Gull has a sturdier bill, thick white crescents around the eye and a dark half-hood in winter. Bonaparte's Gull has a thin black bill, a paler gray back and, outside the breeding season, a white head with a small dark ear spot. With those few marks in mind, Franklin's Gull vs. Bonaparte's Gull becomes one of the more rewarding puzzles on a prairie lake or slough.

How can you tell Franklin's Gull from Bonaparte's Gull at a glance?

Check four features in order: wingtip pattern, back color, bill shape and head pattern. The table below sets out the main differences between adult birds. Young birds are covered in their own section further down.

Feature	Franklin's Gull (Leucophaeus pipixcan)	Bonaparte's Gull (Chroicocephalus philadelphia)
Outer wing (adult)	Black tips separated from the gray wing by a white band; small white spots at the very tips	White wedge along the leading edge of the outer wing; narrow black trailing edge to the tips
Back and upper wing (mantle)	Medium-dark slate gray	Pale silvery gray
Bill shape	Relatively stout and deeper at the base; red in breeding season, mostly dark in winter	Thin, fine and pointed; black all year
Eye	Bold, thick white crescents above and below the eye	Thin white crescents, less obvious
Breeding head	True black hood	Blackish-slate hood that can look black at a distance
Nonbreeding head	Dark half-hood across the back of the head; white forehead	Mostly white head with a neat dark spot behind the eye
Legs	Dark red to blackish	Orange-red in breeding season, pinkish in winter
Build and flight	Deeper-bodied, broader-winged, easy and buoyant flight	Slimmer and lighter, quick tern-like wingbeats
Prairie nesting habitat	Large colonies on floating nests in marshes	Does not nest on the open prairie; nests in conifers in the boreal forest farther north

What does each species look like?

Both are small, hooded gulls, clearly smaller than the familiar Ring-billed Gull. Each has a distinct look once you know what to expect.

Franklin's Gull

Franklin's Gull (Leucophaeus pipixcan) is the classic gull of prairie marshes. A breeding adult has:

a jet-black hood
bold white eye crescents that almost meet behind the eye
a red bill
a dark gray back

In spring, the white underparts often carry a soft rosy-pink wash. This species is unusual among gulls because adults go through two complete molts each year. A molt is the regular replacement of feathers. Because of this, adults tend to look fresh and neat rather than worn.

Bonaparte's Gull

Bonaparte's Gull (Chroicocephalus philadelphia) is a dainty, pale gull. It looks delicate, almost like a tern. A breeding adult has:

a blackish hood
a fine black bill
orange-red legs
a pale gray back

In flight, the white flash on the outer wing catches the light, even when the bird is far away over open water. On the prairies it is mainly a migrant. It feeds over larger lakes and reservoirs, picking small prey from the surface and sometimes catching insects in the air.

How does the wing pattern differ in flight?

The wing pattern is the most reliable field mark, and it works for adults of both species at long range. The primaries are the long outer flight feathers that form the wingtip, and they are what you should watch.

Franklin's Gull: The dark gray wing ends in a black wingtip. A white bar separates the gray from the black, and the black ends in small white spots. The trailing edge of the wing is broadly white. From a distance, the wingtips look dark.
Bonaparte's Gull: The outer primaries are mostly white. This forms a pale triangle along the leading edge of the outer wing, with a thin black line along the tips. From below, the outer wing looks pale and almost translucent against the sky.

This matters because many perched gulls hide their wingtips, and flocks on the water often turn away. One wing-stretch or a short flight is often enough to settle the identification.

How do bill shape and head pattern help?

Bill shape is a useful second check when the wings are folded. Franklin's Gull has a sturdier bill with a slightly drooping tip, and it looks heavier for the bird's size. Bonaparte's Gull has a slender, needle-like black bill that gives its face a gentle, pointed look.

The head pattern adds more support. The thick white eye crescents of Franklin's Gull stand out against both the black breeding hood and the dark winter half-hood. On Bonaparte's Gull, the eye markings are thin and easy to miss. In late summer and fall, a Franklin's Gull with a dark rear crown looks quite different from a Bonaparte's Gull with a clean white head and one dark ear spot.

How do you identify them in nonbreeding plumage and as young birds?

Nonbreeding plumage is the plumage worn outside the nesting season, mostly from late summer through winter. Head pattern is the key mark at this time of year.

Nonbreeding Franklin's Gull: A dusky half-hood covers the rear of the head, like a dark cap pulled back. The forehead is white and the eye crescents are bold. The bill is mostly dark.
Nonbreeding Bonaparte's Gull: The head is mostly white with a crisp dark spot behind the eye, sometimes with a faint gray smudge over the crown. The bill is black and the legs are pink.

Young birds in their first fall and winter are trickier, but the same head patterns still help.

First-year Bonaparte's Gull: Look for a dark diagonal bar across the inner wing, called a carpal bar, which together with the dark outer wing forms a zigzag "M" pattern in flight. It also has a narrow black band at the tip of the tail and the same dark ear spot as the adult.
First-year Franklin's Gull: It shows a gray back, brownish wings, a dark half-hood and a black tail band that does not reach the outermost tail feathers. It lacks the strong "M" pattern of a young Bonaparte's.

How do body size and behavior compare?

Body size helps only a little, because the two species overlap in length. Both fall within roughly 28 to 38 cm (11 to 15 inches) depending on the source and the individual. In the field, it is more useful to judge shape than measurements.

Bonaparte's Gull looks slim and light, with narrow, pointed wings and quick, buoyant wingbeats.
Franklin's Gull looks fuller in the chest and broader in the wing, with a relaxed, floating flight.

Behavior gives further hints on the prairie. Franklin's Gulls often gather in large, noisy flocks over fields, following farm machinery to catch insects and other prey stirred up from the soil. They also swirl above marshes, catching flying insects. Bonaparte's Gulls are more often seen over open water, dipping to the surface or hovering briefly before picking up food.

When and where will you see each species on the prairie?

Season and habitat often suggest which gull you are watching before you raise your binoculars. Use them as a first hint, then confirm with field marks.

Spring (roughly April to May): Franklin's Gulls arrive in flocks and settle into marsh colonies. Bonaparte's Gulls pass through on their way to boreal nesting areas, often stopping briefly on lakes and large wetlands.
Summer: Franklin's Gull is the expected hooded gull around prairie marshes and nearby fields. Bonaparte's Gull is scarce on the open prairie because it nests farther north, in trees.
Late summer and fall: Franklin's Gulls form large pre-migration flocks before heading south. They travel all the way to the Pacific coast of South America for the winter. Bonaparte's Gulls move south later and may linger on big lakes and reservoirs until the water freezes.

In practical terms, a hooded gull over a cattail marsh in June is very likely a Franklin's Gull. A small, pale gull flashing white wingtips over a reservoir in late October deserves a careful look for Bonaparte's Gull.

How should you identify them on your next outing?

A steady routine keeps identification calm and reliable, especially with a mixed flock. Work through these steps:

Note the setting first. Record the date, the habitat (marsh, field, lake or reservoir) and whether the birds are feeding, resting or flying.
Compare with a known gull. If Ring-billed Gulls are present, use them as a size and color reference. Both target species look smaller, and Franklin's looks noticeably darker-backed.
Wait for the wings. Watch for a bird to stretch or take off. Look for black wingtips with a white band (Franklin's) or a white leading-edge wedge (Bonaparte's).
Study the head and bill. Check for bold eye crescents and a stout bill (Franklin's), or a thin black bill and an ear spot (Bonaparte's in nonbreeding plumage).
Look at the legs. Dark red to blackish legs suggest Franklin's. Orange-red or pink legs suggest Bonaparte's.
Consider age. If you see a zigzag "M" on the upper wing and a black tail tip, think young Bonaparte's Gull.
Write it down before checking a guide. Your own notes stay honest and help you learn.

What should you record in your field notes?

Good field notes describe what you actually saw, so you can confirm an identification later and notice seasonal patterns over the years. For each sighting, try to note:

date, time, location and weather
number of birds, and whether they were in a single-species or mixed flock
wingtip pattern, back color, bill color and shape, and head pattern
leg color, if visible
behavior, such as following a tractor, hovering over water or resting on a mudflat
a quick sketch of the wing, even a rough one, showing where the white and black fall

Over a few seasons, these notes show the rhythm of the prairie: the first Franklin's Gulls in spring, the summer colonies and the late-fall Bonaparte's Gulls on open water.

How can you prepare and watch respectfully?

A little preparation makes gull watching more comfortable and kinder to the birds. Binoculars are enough for most views. A spotting scope helps with distant flocks on large lakes. Prairie wind can be strong and cold, especially in spring and late fall, so bring layers and something warm for your hands.

Franklin's Gull colonies nest on floating mats of vegetation in marshes and are easily disturbed. Watch from roads, trails or the shoreline at a distance where the birds carry on calmly. If adults rise and call overhead, you are too close, and stepping back protects eggs and chicks. Stay on established paths so you do not trample wetland edges, keep dogs leashed and never feed gulls. Quiet patience usually brings the best views anyway. Settle in, let the flock relax, and sooner or later a bird will lift its wings and show you exactly which gull it is.