Studying bill and eye characteristics in European Herring Gulls

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.

Study material

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…

Inspiration

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.

Bill characteristics

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.

Bill characteristics in European Herring Gulls (Larus argentatus argenteus). May 2013, Vlissingen, The Netherlands.

Bill characteristics in European Herring Gulls (Larus argentatus argenteus). May 2013, Vlissingen, The Netherlands.

Tip: open the image in a new tab so that you can refer to it while reading the text.

Physical characteristics

Let’s focus on comparing a few physical characteristics:

Figure of various bill characteristics.

Figure of various bill 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.

Bill length

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.

Gape curvature

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.

Gape curvature has a direct effect on the general appearance.

Gape curvature has a direct effect on the general appearance.

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).

Gonydeal angle

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?

Bill coloration

Let’s now take a look at the different color markings.

Gonys spot

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.

Black markings

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).

Eye characteristics

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 haracteristics in European Herring Gulls (Larus argentatus argenteus). May 2013, Vlissingen, The Netherlands.

Eye haracteristics in European Herring Gulls (Larus argentatus argenteus). May 2013, Vlissingen, The Netherlands.

Eye speckling

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:

0 I II III IV V
0% 0-1% 1-5% 5-10% 10-20% >20% Total
Male 1 14 8 1 0 0 24
Female 12 9 4 0 0 0 25
Unknown 1 1 1 1 0 0 4

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.

The color of the orbital ring ranged from light yellow to dark yellow.

The color of the orbital ring ranged from light yellow to dark yellow.

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.

Conclusion

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.

Acknowledgements

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.

References

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)

Gull topography

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3 thoughts on “Studying bill and eye characteristics in European Herring Gulls

  1. With regards to ‘Moult around the eye’… I’d always just assumed that bare patches of skin around a gull’s eyes were due to parasites or eye infections – and thus rubbing the itchy eye so much that the feathers fall out. Or maybe because of fighting. I’m probably wrong. I never really thought too much about it until you mentioned it… 🙂

  2. I live in Blackpool Lancashire England and of course there are many many gulls around here. Last year and this year several pairs have been nesting on the chimney pots on the houses in our road. A particular pair kept pinching the crunchy cat food I left out for a stray cat. Needless to say I began leaving food particularly for the gulls. Whether it was the male or the female or another pair of gulls, I do not know, but they came and stood on the wheely bins outside my dining room window and knocked quite purposefully until they got my attention and consequently fed them. Imagine my surprise when a gull turned up again this year and promptly started to knock on the window to be fed. I have been feeding them crunchy cat food again and they seem to come in the morning and knock on the window to be fed. As I say, I do not know if they are one pair, one individual bird or a number of birds, I do not know how they would communicate the fact that I put food out for them. When the individual has knocked on the window, they walk along the wall towards a garden storage box and I put the food in a bowl on there for them. They are obviously nervous and keep a look out for the cats, who sometimes come and pinch the food, but this does not put them off and they come back every day. I this common behaviour? I get a very close view of them through the window, which is directly infront of my desk. But I am afraid, even though I have studied your photographs, I cannot tell if it is one particular bird or a pair or several. Any clues at all as to how to distinguish male from female would be appreciated. It seems from your study that there is really no specific difference, Am I right? – Your study was very interesting and quite enlightening and there seems to be a great deal of difference between each bird, so as you say unless you can study more than one at a time, it is very difficult to tell them apart.
    Thanks for your interesting study.
    Rita Lane (Mrs)

    • Hi Rita,

      Many thanks for contacting me with your interesting story.

      Gulls have a high site fidelity and tend to return to the same spot to breed or to spend the winter. Herring Gulls can also adapt to feed on a particular food source or adopt a way of feeding: some only eat sea food while others are real city birds. Your gulls have specialized in feeding on cat food and in learning how to attract your attention. Although this behaviour is not uncommon, it is very individualistic. It is very likely therefore that your cat food eating gulls are the same pair as last year.

      You are right in saying that there are no differences in plumage between male and female. They can only be separated by size (the male is always larger) or by behaviour (the male will regurgitate food for the female and seeing them mating is also a good way of seeing which is which 😉

      To really see if they are the exact same individuals you need to try and find some distinguishing mark or feature (bill pattern, crooked leg, etc), or try and photograph the pattern on the wing.

      One more thing about the behavior, have a look at this video: http://youtu.be/p3HFUCwd28Q

      Regards,

      Maarten

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