All gulls look the same.
Until you look closely, and then you notice minute but distinct differences.
I was able to get a closeup view of adult European Herring Gulls (Larus argentatus argenteus) last Saturday when I was visiting a gull colony near Vlissingen, a location in the south-western part of The Netherlands, close to the North Sea and Belgium.
While I was there, adult gulls were caught, measured and ringed as part of a project to monitor how they disperse in the region.
I was able to take detailed photos of a number of individual gulls, including 53 Herring Gulls. I took photos of the primary pattern of the wing as well as a closeup of the head.
Edit: If you’re reading this article because you are curious how to tell the difference between a male and female seagull in the field, this can be done as follows:
- General impression when seeing an individual gull: male gulls are larger than females. This is especially noticeable in large gull species. Males can also look more fierce while females can look more friendly.
- When both partners are standing next to each other. In gulls, the male is always bigger.
- When one adult gull feeds another adult gull. This is called ‘courtship feeding’ and is part of the ritual to strengthen the bond. The one feeding is always the male.
- When adult gulls are copulating. The way copulation works in gulls means that the male will be standing on top of the back of the female.
Being able to compare individuals (even of the same species) is always a great opportunity to study the characteristics in detail and get more familiar with any variation that may exist.
You might wonder why you would need to study such a common species this way, but the more familiar you get with the common species in your area, the better you will be able to identify species that may closely resemble it (including, or perhaps especially, hybrids).
It is also interesting to be able to recognize geographical differences within a species or its subspecies so that when an individual from such an area visits your local gull patch, you will be able to recognize it more easily.
Anyway, do us larophiles really need a reason to study any type of characteristic in gulls? I think not…
By the way, my inspiration for these types of studies and knowing what to look for are publications such as Phenotypic characteristics and moult commencement in Dutch Herring & Lesser Black-Backed Gulls by the good guys from Gull Research. Well worth a read.
Let’s start with comparing the bill of 25 individuals out of the 53: 11 males, 11 females and 3 individuals of unknown sex. All individuals are adults of unknown age (older than 4th-calendar year).
Note 1: Sexing was performed based on wing length, supported by the general impression of the shape of the head and the shape & size of the bill.
Note 2: All photos were taken using flash light (in the shade as much as possible). The distracting background was replaced in Photoshop by a more neutral one.
Tip: open the image in a new tab so that you can refer to it while reading the text.
Let’s focus on comparing a few physical characteristics:
Note: Because the photos have been taken from different angles and have been resized, it is not possible to derive any exact measurements from them. Any comparison needs to be done by eye.
Much overlap exists in bill length between male and female Herring Gulls.
In Gulls of Europe, Asia, and North America, the following measurements are given for adult L. a. argenteus:
- Male 49.0 – 64.9 (56.5)
- Female 44.6 – 59.1 (50.1)
This overlap seems to be apparent in the examples above as well, with most bills more or less the same size. If we’re looking at some clear differences, then the bill of Female 1 for example seems to be much longer than the bill of Female 3.
Distance between lore and nostril
While studying the photos, it occurred to me that this distance is not constant but seems to be affected by the size of the nostril and the triangular shape of the lore (and perhaps bill length?).
Not a very significant characteristic, but noteworthy nonetheless.
Bill depth (at the base)
Again, much variation exists. Gulls of Europe states:
- Male 17.1 – 21.1 (18.4)
- Female 15.0 – 93 (17.3)
It’s a pity that no exact measurements exist of the 23 individuals in the photo because I’m curious to know how bill depth relates to bill length if at all.
This is one aspect that struck me most during this exercise and one that I had never paid much attention to in the past.
The photos show a clear difference in the way the gape curves downward: from almost straight to clearly curving downwards.
Compare for instance Male 3 with Female 2, or Male 11 with Female 10.
I realized that this has a direct effect on a gull’s general appearance. Note the following two females, where the one with the straight gape has a much friendlier appearance than the one with the curved gape who comes across more sulky.
It had never occurred to me to use it as a distinguishing characteristic, but I will look out for it in the field from now on to see it is of any use.
Length of soft underpart
I’m not sure if this part has an official name (maybe it’s just the throat?), but it struck me that in some individuals this section is very short (Male 3), whereas in others it extends to almost halfway down the bill (Female 6).
Again, this is difficult to measure from the photos because of the different angles at which the photos are taken, but it seems to be pretty constant and not affected much by for instance bill length.
Bill tip extension
From the photos it is clear that in the majority of the individuals (7 males and 9 females) the tip of the bill extends past the lower mandible, varying from just slightly (Female 3) to very clear (Male 2).
Would it have any relation to feeding habits?
Let’s now take a look at the different color markings.
We can see that the gonys spot is mostly orange in all individuals, with the exception of Female 9 where it looks more reddish.
The gonys spot also looks uniform in size across all individuals, covering the area from the gonydeal angle to nearly to the tip of the lower mandible.
When it comes to brightness, we can see that in some individuals the spot is faint (Male 2 and Female 1) whereas in others it is quite bright (Females 2 and 9).
In none of the individuals does the gonys spot extend to the upper mandible.
During the non-breeding season, many adult gulls show black markings on the bill tip. In most individuals this disappears in time for the breeding season, but on some individuals the black markings can be seen well into the summer.
The photos show that 5 males and 2 females have such markings (for example Male 3 and Female 1).
When we turn our attention to the eye and the area around it, we can compare the following characteristics:
- Eye speckling
- Orbital ring color
- Moult around the eye
Eye speckling is scored on a scale from 0 to 5:
- 0 – No speckling
- 1 – Between 0 and 1% speckling
- 2 – Between 1 and 5% speckling
- 3 – Between 5 and 10% speckling
- 4 – Between 10 and 20% speckling
- 5 – Between more than 20% speckling
For examples, see Phenotypic characteristics and moult commencement in Dutch Herring & Lesser Black-Backed Gulls page 5.
After applying a score to the 53 individuals that were photographed, we get the following result:
Here we see the first main difference between males and females: only 1 male (4 %) was scored with 0% speckling, whereas 12 females (48%) received the same score.
Not surprisingly, the data shows that speckling in Herring Gull is quite limited with only 2 individuals receiving a score of 3 (5-10% speckling) and no individuals receiving a score of 4 or 5.
Note: the 2 individuals with the high score of 3 can be seen in the image above as Male 7 and Unknown 2.
Orbital ring color
Orbital ring color in Herring Gulls ranges from yellow and dull orange to greyish-pink and occasionally red (source: Gulls of Europe).
Out of the 53 individuals on my photos, 47 showed a light yellow orbital ring, with the other 6 (5 males, 1 female) showing a more darker yellow ring.
Moult around the eye
Out of the 53 Herring Gulls, 14 (26%) showed moult around the eye: 6 males, 5 females and 3 individuals of unknown sex.
An example can be seen in the orbital ring color image above, on the left.
As far as I’m aware, this moult is the start of the moult to basic cycle plumage.
This has been a very interesting exercise for me in which I picked up quite a few new things.
It was not surprising to see the large variety because that is what gulls are known for, but it was good practice to focus on these specific characteristics for the first time. This is actually the reason why I keep a blog: to get more out of my photo material and to continuously keep learning about these fascinating species.
More to come?
During the same session I also photographed 15 adult Lesser Black-backed Gulls. I might write up a similar post in the near future to see what that brings us.
My thanks goes to Roland-Jan Buijs for inviting me to attend his ringing session, for allowing me to make photos and of course for looking after the gulls.
The bird in the hand (Bird ringing manual, PDF)
Adult European Herring Gulls in May on Gull-Research.org
Phenotypic characteristics and moult commencement in breeding Dutch Herring Gulls Larus argentatus & Lesser Black-Backed Gulls Larus fuscus (Web site version with many additional photos)