Ring-billed Gulls vs Common Gulls: comparison from a Dutch perspective- 201402

Adult Ring-billed Gull (left) vs adult Common Gull (right)

Ring-billed Gulls Larus delawarensis are common visitors to Europe with frequent sightings in countries directly bordering the North Atlantic such as Ireland, Spain and Portugal.

Here in the Netherlands however, they are considered rare (see list of observations on Waarneming.nl) and most sightings are quickly uncovered as regular Common Gulls Larus canus due to unfamiliarity by the observer with both Ring-billed Gull and Common Gull.

When I traveled to the USA recently for a short gull-watching trip (see Gull watching in the southern Lake Michigan region (USA) – 201402), one of my aims was to get familiar with Ring-billed Gulls and to find out exactly what differentiates them from Common Gulls.

Below are some personal reflections based on my observations.

Note #1: This article is nothing more than a personal exercise in comparing 2 random groups from both sides of the Atlantic; it should by no means be seen as a definitive comparison between these 2 species; this requires a far higher number of individuals.

Note: #2: All Common Gulls are of unknown origin and photographed in the Netherlands in the months of December, January and February.

First-cycle, second-calendar year individuals

First-winter Ring-billed Gulls in their second-calendar year can be differentiated from first-winter Common Gulls by comparing the following 9 aspects:

Tail
Greater coverts
Median coverts
Bill
Head
Tertials
Mantle
Underwing
Outer secondaries and inner primaries

So, let’s compare some of the Ring-billed Gulls that I photographed with some random Common Gulls from my archive.

1. Tail pattern

The tail pattern of a 1st-cycle Ring-billed Gull usually shows additional tail-bands and markings on especially the outer tail feathers. In Common Gull the tail band mainly consists of a clear-cut tail band with few or no markings above it.

A low percentage of Ring-billed Gulls can display the same pattern as a Common Gull.

Tail pattern comparison.

As can be clearly seen from the above comparison, very little variation exists in the tail pattern of a Common Gull, whereas the tail of a Ring-billed can be quite boldly patterned. Note though how #2 is indistinguishable from that of any of the Common Gull patterns.

Q. So how does the tail pattern help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Well, tail patterns such as those in #1, #3, #4 and #5 should immediately attract attention, but any of the patterns seen in #6 to #10 should not automatically exclude a Ring-billed Gull (based on pattern #2).

2. Greater coverts pattern

Unlike Common Gulls, 1st-cycle Ring-billed Gulls may replace their greater coverts by adult-looking, second-generation feathers. These feathers are the same color as the mantle. Also, the inner greater coverts can show barring.

The first-generation greater coverts of the Common Gull wear and bleach as the winter progresses and may therefore look pale, but will never be the same color as the mantle.

Greater coverts comparison.

Note the number of replaced greater coverts in the Ring-billed Gulls, wheres the coverts in the Common Gulls are all first-generation. Bird #1 shows the distinct barring on the inner coverts.

Q. How does the pattern on the greater coverts help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any gull in which the greater coverts are of the same colour as the mantle and which have distinct barring on the inner greater coverts should definitely be scrutinised further.

3. Median coverts pattern

In Ring-billed Gull, the median coverts are usually light with triangular markings, whereas those of the Common Gull are more pronounced and have rounded centers. Such rounded centers can sometimes also be seen in Ring-billed Gull though.

This is a very subtle feature and obviously needs close-up views or detailed photographs.

Median coverts comparison.

Q. How does the pattern on the median coverts help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any gull of which the median coverts does not show a rounded center should definitely be scrutinised further. However, a rounded center should not exclude a Ring-billed Gull.

4. Bill shape and pattern

The bill of a Ring-billed Gull is stouter than that of Common Gull, with a more curved upper mandible, whereas the bill of a Common Gull is thinner and pointier.

The pattern of a Ring-billed Gull is quite distinctive: a pink base with a black tip, reminiscent of Glaucous Gull. While a Common Gull can also show this pattern, a Ring-billed Gull will not display the green/greyish colouration of a Common Gull.

Bill comparison.

Q. How does the bill shape and coloration help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any gull with a green or yellow tinge can be discarded as a Common Gull. Birds of which the bill is pink with a black tip should not be excluded as a Ring-billed Gull.

5. Head and breast patterning

The head and breast pattern on a Ring-billed Gull is more extensive than on a Common Gull, with more streaks or spots and a markedly spotted hindneck.

Head, breast and flanks comparison.

Note that the hindneck of Common Gulls #6 and #8 are as dense as Ring-billed Gull #2. Much overlap seems to exist therefore between both species.

Q. How does the pattern on the head, breast and flanks help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. This characteristic is probably not reliable enough to use it for separating Ring-billed Gull from Common Gull.

6. Tertial pattern

The tertials of the Ring-billed Gull usually have thinner white edges than those of a Common Gull and are usually more worn as the winter progresses.

Tertial comparison.

Note the replaced tertial in individual #1 and the classic tertial pattern of a Common Gull in #5.

Q. How does the tertial pattern help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any individual with broad white tertial edges will not be a Ring-billed Gull.

7. Mantle color

The mantle color of a Ring-billed Gull is lighter than that of a Common Gull: Kodak 3-4(5) compared to 5-6(7) and therefore is more comparable to that of a Black-headed Gull: 4-5(6).

See the photos used for the tertial comparison above. (Note that light-fall, light conditions (sun or shade), photo editing, and the monitor on which the image is viewed greatly influences the way the mantle tone is perceived.)

Q. How does the mantle color help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any individual that is clearly lighter than a Common Gull is a good candidate. This difference can best be compared with nearby Common Gulls and/or Black-headed Gulls.

8. Underwing pattern

The underwing of a Ring-billed Gull is said to show axillaries and greater coverts with narrower and darker tips than those of a Common Gull and the light coverts contrast well with the dark secondaries.

Common Gulls are said to have a more evenly dark pattern.

Underwing pattern.

The photos show much overlap between the 2 species; if anything, the secondaries look darker in Ring-billed Gull than in Common Gull.

Q. How does the underwing pattern help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Due to overlap in variation between both species, it is probably best not to pay too much attention to this feature. Evenly dark secondaries may point towards Ring-billed though.

9. Outer secondary and inner primary pattern

Ring-billed Gulls can show diamond-shaped, sub-terminal markings on inner primaries P1-P4.

From studying my photos, the darker markings on the tips of the outer secondaries can be seen to gradually reduce from secondary S5 outwards so that the height of the marking on secondary S1 matches that of the marking on primary P1. This creates a light triangle, something which I have not observed in Common Gulls (where all secondaries are equally dark), nor have come across in literature.

Outer secondary and inner primary pattern.

#1 and #2 show the light triangle created by the tapering markings on the outer secondaries. #2 Also shows the diamond-shaped markings, especially on P5 and P4.

Q. How does the pattern on the outer secondaries and inner primaries help us recognize a first-cycle Ring-billed Gull in the Netherlands?

A. Any individual with a light triangle across the outer secondaries and inner primaries, and/or diamond-shaped markings on the inner primaries is a good candidate for Ring-billed Gull.

Summary

So what makes up the ‘perfect’ first-winter Ring-billed Gull?

Extensive patterning on the tail
Greater coverts the same color as the mantle (replaced feathers)
Distinct barring on the inner coverts
Median coverts with triangular pattern
Stout bill, not green or yellow-ish
Light triangle across outer secondaries and inner primaries
Diamond-shaped markings on inner primaries

Second-cycle, third-calendar year individuals

Ring-billed Gull is a 3-year gull, meaning that the adult plumage is acquired in its 3rd year. Second-year individuals (in their 3rd-calendar year) therefore will look as an adult: a light-mantled, pale-eyed gull with a distinct black band on the tip of the bill. (For additional features, see adult below.)

They can however be aged by the following characteristics*:

Darker outerwing, caused by black on the primary coverts and alula
P10 at best with a small mirror
P9 with no mirror
Outer primaries P6-P10 without a white tip (apical spot)
Brown lesser coverts
Dark markings on underwing coverts
Dark markings on the tail
Dark markings on the secondaries
Can show black spots on the tertials

*Note: It is important to see this in a Dutch context where most observed Common Gulls are of sub-species Larus canus canus, but that some Ring-billed features can also occur in the eastern taxa Russian Common Gull Larus canus heinei. This is out-of-scope for this article.

Q. Which of these characteristics help us separate a 3rd-calendar year Ring-billed Gull from a 3rd-calendar year Common Gull in the Netherlands?

A. A 2nd-cycle, 3rd-calendar year Common Gull will never show dark markings in the secondaries and only rarely dark markings on the tail. P9 of a Common Gull will usually have a small mirror and the underwing will be unmarked.

Second-cycle Ring-billed Gull showing the characteristic immature features: dark markings in the tail, secondaries and underwing, and no white tips to the outer primaries. This individual also has no mirror on P10.

Second-cycle Ring-billed Gull showing the characteristic immature features: dark markings in the tail, primary coverts, secondaries and underwing, and no white tips to the outer primaries. This individual also has no mirror on P10.

Second-cycle Common Gull showing no markings in the tail, secondaries or underwing. Both P9 and P10 have a mirror.

Second-cycle Common Gull with rare black markings in the tail.

Tertial spots and tertial crescent

Tertial spots are as regular a feature in second-cycle Ring-billed Gulls as they are in Common Gull.

Similar to adults, second-cycle Common Gulls show a much broader white tertial crescent than Ring-billed Gulls.

Tertial spot comparison.

Adults

Although it should be quite straight forward to distinguish an adult Ring-billed Gull from a Common Gull, lets compare some of the main features.

Compared to an adult Common Gull, an adult Ring-billed Gull is different in the following aspects:

Lighter upper parts
A thicker, stouter bill
Smaller mirror on P10
Smaller mirror on P9 or no mirror on P9 at all
Rarely a mirror on P8
No black on P4
Pale yellow iris
Thinner tertial crescent

Bill and eye color comparison

Bill and eye color comparison.

Note that the bill pattern on the Ring-billed Gulls is very distinct, while the ‘ring’ on the bill of a Common Gull is very faint.

Judging the bill shape and size may look straightforward but can be tricky in the field.

Pitfall: Some Common Gulls can show a light iris and should not be treated as a Ring-billed Gull on that feature alone.

Primary pattern

Primary pattern comparison.

Q. How does the pattern on the primaries help us recognize an Ring-billed Gull in the Netherlands?

A. Any individual without a mirror on P9 should immediately attract attention.

Tertial crescent

Tertial crescent comparison.

Probably one of the key features of spotting an adult Ring-billed Gull in a group of Common Gulls (especially from afar) is its much reduced white tertial crescent.

Vocalization

The vocalization of Ring-billed is lower in tone, more nasal than Common and reminiscent of Herring Gull.

Unfortunately I don’t have many recordings of Common Gull vocalizations and they don’t match the type of Ring-billed Gull calls that I was able to record in Milwaukee, but I thought it best to include 2 tracks.

Comments

Although this has been a fully unscientific and random comparison, it has nevertheless been a very interesting and useful exercise for me.

It has highlighted some features that I would otherwise not have noticed (such as the barring on the inner primaries in first-cycle birds) and has made me more comfortable in knowing what to look out for should I come across a Ring-billed Gull-candidate here in the Netherlands.

It has been great to observe Ring-billed Gulls in such large groups and from such a short distance. Unfortunately the same cannot be said of Common Gulls and I was surprised with how few photos I had in my archives of this species.

Finally, I hope that my findings are useful for other birders as well.

Locations

The majority of the Ring-billed Gull photos in this article were taken at the beach at the BP refinery at Whiting, Indiana, USA, adjacent to Lake Michigan.

A few additional photos were taken at the car park of the Lake County Fairground, Libertyville, Illinois, USA.