A Bit of a Mix…

Winter has finally (and seriously) arrived here in Holland with temperatures staying below zero degrees Celcius even during the day. Good news for gull observers because the cold weather always brings gulls closer to cities with food resources such as arable lands unsuitable for foraging.

Last Sunday I was visiting a location just on the outskirts of Leiden where two bodies of water meet up (the Oude Rijn and the Zijl) which when frozen attracts a few hundred gulls (Common, Black-headed and Herring). The fact that there is open water under a bridge nearby, the city center at close proximity to go foraging and no disturbance by humans makes this an ideal resting place for them.

The previous day I had already observed a color-ringed pair of European Herring Gulls, so I was eager to see what this visit would bring.

Initially it seemed disappointing because hardly any ring could be read; for some reason all the gulls preferred to go sit on the ice as soon as they landed. Three hundred gulls on the ice and no legs to look at…

I had already packed up to go and try my luck elsewhere when I saw an adult gull fly across to join the group.

It immediately attracted my attention because it looked out of place. It was a gull the size of a Herring but much darker. It came in from the right, flew over the main group and eventually landed on the far side (they never land close in front of you, do they?) and somewhat apart from the group.

My first reaction was Lesser Black-backed Gull which would account partly for my interest because this species breeds here in The Netherlands but is mostly absent during the months of October – February/March (with only a handful of individuals staying behind). Up to that point I had only watched it through my binoculars but it was definitely worth setting up the telescope again for a better look.

Presumed Lesser Black-backed Gull x European Herring Gull (Larus fuscus x Larus argentatus). Leiden, The Netherlands, 5 Februari 2012.

What I saw was a gull with a dark gray mantle which was much darker than a Herring Gull but also much lighter than the Lesser Black-backed Gulls that I’m used to seeing in The Netherlands during the breeding season.

Typical Lesser Black-backed Gull, (L.f. graellsii), Green M.ALZ. Texel, Kelderhuispolder, Gull colony, The Netherlands, 24 June 2011.

Typical European Herring Gull (Larus argentatus), Texel, Kelderhuispolder, Gull colony, The Netherlands, 7 May 2011.

Other characteristics that I noted were:

• Bright yellow bill with red gonys spot
• Light yellow eyes with red eye ring
• Square head
• Round body shape, not elongated
• Broad tertial crescent
• Black primaries with broad white tips
• Pink legs with a yellow hue

Despite the long distance I was able to take some photos through my telescope with my pocket digital camera. Fortunately it obliged by resting and preening for a few minutes.

Presumed Lesser Black-backed Gull x European Herring Gull (Larus fuscus x Larus argentatus). Leiden, The Netherlands, 5 Februari 2012

After checking if the photos had come out alright and briefly looking up I noticed that the gull was not there anymore but instead was flying towards me. I quickly had to unpack my Nikon camera which was set up with my 300mm/f4 and 1.4 converter and I was able to take a few flight shots when it circled once before flying away to the West.

Presumed Lesser Black-backed Gull x European Herring Gull (Larus fuscus x Larus argentatus). Leiden, The Netherlands, 5 Februari 2012

Presumed Lesser Black-backed Gull x European Herring Gull (Larus fuscus x Larus argentatus). Leiden, The Netherlands, 5 Februari 2012

Presumed Lesser Black-backed Gull x European Herring Gull (Larus fuscus x Larus argentatus). Leiden, The Netherlands, 5 Februari 2012

I left the area feeling happy to have seen what I then thought to be a graellsii-type Lesser Black-backed Gull which in itself is uncommon (the species which breeds here is a “hybrid” version of intermedius x graellsii, referred to as Dutch intermedius) but even more so during the winter.

It wasn’t until I was studying the photos at home and submitting my observation to waarneming.nl that I started to get the feeling that something didn’t quite add up.

Still convinced that I was dealing with a Lesser Black-back, I focused on specific characteristics. The primary pattern for starters did seem to match that of a graellsii:

Lesser Black-backed Gull (L.f. graellsii), London GN64662 with a primary pattern matching that of the mystery gull (except the white mirror on P9)."

What concerned me most though was the body shape. A Lesser Black-backed Gull is one of the most elegant of large gulls with its long wings. In rest this creates a long primary projection while in flight the tips of the wings are pointy. My gull had a much more rounded body, short primary projection and more rounded wings. It also showed a withdrawn neck in flight.

I still also was not able to find to find examples of Lesser Black-backs with such a light gray mantle.

The other odd thing was the leg color: much too pink for a Lesser Black-back, it should match the yellow of the bill.

It was then that the ‘H’ word entered my mind: hybrid!

Hybrids are a common pitfall for gull watchers because inter-breeding is common among gull species resulting in diverse mixes in plumages and characteristics.

I had yet to see one myself though so the thought of dealing with a hybrid took some time for me to occur. When it did though, I was reminded by a similar hybrid of which I had seen many photos posted online. See this observation, this set, and this set.

Now it made much more sense to me and it certainly explained the mix of characteristics which could not be attributed to one single species.

I logged my observation online (marked ‘uncertain’) and asked for confirmation on a Dutch forum. This resulted in some interesting feedback of a possible inclusion of a Yellow-legged Gull (Larus michahellis) which would account for the body shape but did not explain the dark mantle. In the mean time my uncertain observation online was approved and I have left it at that: a presumed hybrid Lesser Black-backed Gull x European Herring Gull.

All in all a very interesting exercise and a good learning moment. I am also sure that I will consider dealing with a hybrid much more quickly in the future.

Paired Up

As early as the end of December, I have seen adult European Herring Gulls (Larus argentatus argenteus) showing interest in each other and showing obvious signs of being a couple. It is known that Herring Gulls already pair up on the wintering grounds far away from the colony and it so happened that I was able to witness this myself on one of my local gull patches.

European Herring Gulls (Larus argentatus argenteus) Green F.AAT (left) together with Green M.ABB (right). Standing next to each other, the size difference between the female on the left and the male on the right can be clearly seen. Leiden, The Netherlands, 4 February 2012.

Both individuals have been ringed in the breeding colony on the isle of Texel in the north of Holland: the female on May 16 2009 and the male also on May 16 but in 2007.

Records of paired partners outside the colony for this project are rare, making this quite a unique observation. They were seen as part of a large group of mixed gulls (some 300) consisting of Herring Gulls, Common Gulls and Black-headed Gulls. They sometimes stood close together but also apart from each other and spent their time preening, drinking and resting. There was no obvious interaction between the two of them.

European Herring Gulls (Larus argentatus argenteus) Green F.AAT (left) together with Green M.ABB (right). Leiden, The Netherlands, 4 February 2012.

The male, green M.ABB. Leiden, The Netherlands, 4 Februari 2012.

The female, green F.AAT. Leiden, The Netherlands, 4 Februari 2012.

Life history

In 2007 and 2008, no partner was recorded for M.ABB but it did breed during those years, probably with an un-ringed female.

An un-ringed partner was captured in 2009 and ringed as F.AAT (note that for this project, codes starting with M indicate a male and those starting with F indicate a female. Codes are issued based on biometric measurements). She laid 2 eggs of which 1 was successfully incubated and reared.

In 2010 they had a 3-egg clutch, all of which were incubated.

In 2011 the male was seen only 3 times within the colony, the female was not observed at all during that whole year. The last time F.AAT was observed was on 9 August 2010 on Texel, with the next observation the one by me on 4 February 2012. It’s nice therefore to be able to show that she is still around and together with her partner. Hopefully I will be able to visit the colony again this year and see them both there.

I had already seen M.ABB a few times in August and September of 2011. It stayed in the Leiden area to finish its primary moult. For images, see this Flickr collection.

Just in Time…

In my post Old Acquaintance early November I wrote about the return of 23-year old Black-headed Gull (Chroicocephalus ridibundus) with Dutch ring Arnhem 3431752.

This observation made it clear that the ring (made out of aluminum) was in such a bad state that it would probably not be long before the ring would be lost.

State of the ring on 13 November 2011, Leiden, The Netherlands.

 

Because of the old age of this gull, it would have been a shame for it to lose the ring and for us not being able to follow it over the coming years. Plans were therefore made to try to capture it and fit it with new rings.

To increase the chance of capturing it again, a pattern of its whereabouts was trying to be established. Fortunately, gulls have a high site-fidelity (preference to stay at or near a particular location) and it was seen on-and-off at various locations within a small area. It also turned out that it was easy to attract it with bread, but that it would only feel comfortable on the ground when there were not too many other gulls around. As soon as the group was too large, it would take off again.

On Saturday December 24 the first attempts were made but these were unsuccessful because of the group of gulls being too large and due to too much disturbance by passers-by.

A second attempt on Sunday the 25th at a location nearby turned out to be successful. It was caught and re-fitted with a metal ring and a color ring. Because the aluminum ring was set tightly on the right foot, the metal ring (code Arnhem 3.729.911) was placed on the right tibia (upper leg) instead. A color ring (White E0TU) was added to make the individual better recognizable (re-sightings of color-ringed birds are far higher than those wearing only metal rings).

We will have to see how this bird will react to its re-capture and if it will stay in the area; it is known for older birds which are caught to lose their habits and for instance move to a different area. Wherever it might end up, we hope to receive many re- sightings of this individual for many more years.

Shortly after being caught: the old ring is set tight just above the foot.

 

The old ring showing heavy wear; the indentations at the top are caused by the fact that the ring was positioned upside down.

 

The new rings being fitted.

 

Being measured; based on the length of the distance between the head and tip of the bill, this individual is determined to be male.

 

The head pattern of this individual during winter consists of only a small ear spot and very faint bands across the head.

 

The pattern of the primary feathers; P9 shows a black mark.

Caught a Casp!

Dutch bird ringer Frank Majoor visited my home town of Leiden, The Netherlands, yesterday to ring some Black-headed Gulls as part of one of his projects.

During one of the sessions I noticed a first-calendar year Caspian Gull (Larus cachinnans) standing between a small group of European Herring Gulls. It stood out not only because of the different plumage (white head, distinctive scapular pattern and a few moulted wing coverts), but also because of its large size and thin, tall legs.

First-calendar year Caspian Gull in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

 

Caspian gulls are quite common in The Netherlands but the number of observations of this type of gull are quite low in the Leiden area (partly because not many people keep track of gulls here).

It only took Frank a few moments to catch it, enabling us to take a close-up look of this magnificent bird. What struck us immediately was its large size (especially the bill), which made it quite a challenge to take its measurements, especially using equipment aimed for measuring Black-headed Gulls!

Fortunately Frank carries with him rings for various types of birds, including large gulls. This bird was to be fitted with a metal ring (ringing station Arnhem, code 5463250) and a color ring (Yellow FF) provided by Roland-Jan Buijs. After a quick call to Roland-Jan to make sure the rings were fitted in the right position (metal on the right tibia, color on the left tibia), we made a few identification photos and then released it. It will be interesting to find out where it will be observed over the next years!

First-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

 

Tail pattern of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

 

Wing pattern of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

 

Flight-shot of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

Some of the identification features of a first-calendar year Caspian Gull, distinguishing it from a European Herring Gull or a Yellow-legged Gull of the same age include:

• Thin high legs, showing much tibia (upper leg)
• Light-grey scapulars with distinctive dark anchor
• Moult in the wing coverts
• White head with light streaking and lack of an eye patch as for Yellow-legged
• Large black bill, somewhat parallel and no blunt tip
• Inner primaries with light inner web and dark outer web (creating a ‘Venetian blind’ effect)
• Small white tips to the inner primaries (apical spots)
• Narrow banding on the tail above the subterminal band

All-in-all a great moment and a nice way to end the year with!

Me with first-calendar year Caspian Gull Yellow FF.

 

Little Gulls

Adult Little Gull, Katwijk aan Zee, The Netherlands, 9 December 2011. This individual is moulting to winter (basic) plumage: the outer two primaries P9 and P10 are not yet fully grown.

 

There where high winds along the coast of Holland today (force 6-8) so I decided to go to the coastal town of Katwijk aan Zee to see if it would produce any nice sightings of proper sea birds being blown ashore. Katwijk is also a good place to pick up the odd Caspian Gull and it’s also a good place to read a ring or two. All good reasons for going over there.

I was not to be disappointed. At my arrival, I first checked a resting place a little bit inland which gulls use to shelter from the fierce winds. A group of some 400 gulls were present consisting mainly of Herring Gulls, Black-headed Gulls, some Great Black-backed Gulls, a single adult Yellow-legged Gull as well as a single first-calendar Black-legged Kittiwake. Among them where 4 color-ringed adult Herring Gulls: 3 with a Dutch ring and one with a German ring. One of the Dutch individuals used to have two rings and can therefore not be positively identified, but we have a good idea of its identity. The gull in question was ringed in 1988, which makes it a 24th-calendar year gull. I’ve only seen 2 gulls of an older age (25 and 26 calendar year respectively).

I then proceeded to the beach where I was met by fierce winds. At the point where a drainage canal meets the North Sea, a group of Black-headed Gulls was feeding off the surface of the water. In between them a group of 3 and later 10 Little Gulls where feeding too. I very rarely get to see this species so was excited to be able to see them so up close (sometimes they came as close as 4 meters).

Their feeding method of a Little Gull consists of moving slowly forward against the wind while hovering above the water with the bill pointed downwards. It then dips to the surface to snatch up their prey, sometimes even sticking the head under water. After following a stretch of water for about 20 meters or so, it uses the strong wind to quickly return to the starting position and repeat the whole process again.

While studying the photos back home, I noticed that some of the adults where still in the process of growing their outer two primaries. It surprised me to see this because I would have expected small gulls to have fully finished their primary moult by this time of year. ‘Birds of the Western Palearctic’ and ‘Gulls of Europe, Asia and North America’ both state that the moulting process ends at the end of November. For these individuals though, I guess it will be more like the end of December though, which is quite interesting to be able to observe.

Adult Little Gull, Katwijk aan Zee, The Netherlands, 9 December 2011. This individual is moulting to winter (basic) plumage: the outer two primaries P9 and P10 are not yet fully grown.

 

Adult Little Gull, ‘walking’ on the water. Katwijk aan Zee, The Netherlands, 9 December 2011

 

Adult Little Gull, ‘walking’ on the water. Katwijk aan Zee, The Netherlands, 9 December 2011

 

Adult Little Gull,  Katwijk aan Zee, The Netherlands, 9 December 2011

 

First-calendear Little Gull, with adult Little Gull, Katwijk aan Zee, The Netherlands, 9 December 2011

 

First-calendear Little Gull,  Katwijk aan Zee, The Netherlands, 9 December 2011

 

ID mix-up with Black-legged Kittiwakes

A first-calendar year Little Gull can be easily mistaken for a similar-aged Black-legged Kittiwake:

First-calendar year Black-legged Kittiwake (Rissa tridactyla). North Sea, near the Dutch coast, October 2009.

 

Note the similarities in plumage: both have a dark W-pattern across the wings, a black tail band and a black bill. Key identifiers though are:

Little Gull

• Dark cap
• Dark-centered secondaries, forming a trailing edge

Kittiwake

• Dark neck band

Whiter than White

Bird watching (and gull watching in particular), is all about learning how to recognize and age a bird by looking for the relevant clues in the bird’s plumage. After having learned what a standard plumage looks like for a given species at a given age, any plumage which does not adhere to this standard can be easily recognized.

One non-standard feature though stands out more than the rest and will be picked up by any birder, regardless of its interest in plumage detail: leucism. In short, leucism is a condition in which the color of a feather is absent, thereby resulting in a white feather. Birds which are affected this way can show anything from just a few white feathers to being completely white.

Depending on how the bird is normally supposed to look, the result can be spectacular and some of the birds which I have enjoyed observing most are indeed leucistic.

Partly leucistic Black-headed Gull, in between two regular Black-headed Gulls in winter (basic) plumage. This individual lacks pigment on the head, the mantle, and in the scapulars. Full black pigmentation is present though in the primaries. White LSB, Amsterdam, The Netherlands,  January 2011.

There is a lot of confusion about what leucism actually is and about the types of leucism that exist, and the general public (but also birders), often mistake leucism by albinism.

Pigmentation

What is important to know is that plumage coloration in birds is mostly determined by the pigments melanines and carotenoids.

Melanines

Two types of melanin are present in birds:

• Eumelanin. Responsible for black, gray, and dark-brown feathers.
• Phaeomelanin. Responsible for reddish-brown feathers (when present in a high concentration), or yellow-brown to white feathers (when present in low concentrations).

When combined, they can create colors such as grayish-brown.

Relevant to know also is that in skin and eyes, only eumalin is present (we’ll see the importance of this when discussing albinism.)

Carotenoids

Carotenoids are taken in through feeding and are transformed into color pigments by enzymes. They range in color from pale yellow to scarlet red. Deposition of pigments occurs when the feather starts growing and any abnormal changes to this process are usually caused due to a change in food intake. (Black-headed Gulls can sometimes be seen with a pinkish-colored body; it is understood that this is caused by a change in diet.)

Black-headed Gull with distinctive pink underparts. Leiden, The Netherlands, January 2010.

 

Leucism

Leucism means that the eumalanin and phaeomelanin pigments are partly or completely missing in the feathers. As a result, white or less-colored feathers appear at random parts in the plumage. This can range from just a few feathers to a completely white plumage.

First-calendar year leucistic Western Lesser Black-backed Gull, with white patches in the scapulars, tertials, wing coverts, secondaries, and primaries. Leiden, The Netherlands, August 2011.

 

Adult Western Lesser Black-backed Gull (Larus fuscus graellsii) with one greater primary covert in each wing without any pigment. Interestingly, this individual did not show any leucism the previous season. Texel, The Netherlands, June 2011.

 

Adult Western Lesser Black-backed Gull (Larus fuscus graellsii) with several greater primary coverts in each wing without any pigment. Texel, The Netherlands, June 2011.

 

Adult Black-headed Gull in full winter (basic) plumage, with white feathers in the lower scapulars. Leiden, The Netherlands, December 2010.

 

Adult Black-headed Gull in full winter (basic) plumage, of which some of the scapulars, tertial #3 (on both sides) and greater covert #2 (on the right-hand side) are white. This individual also shows a pink colouration on the breast and in the outer primary shafts. Leiden, The Netherlands, November 2010.

 

Partly leucistic Black-headed Gull. This individual lacks pigment on the head, the mantle, and in the scapulars. Full black pigmentation is present though in the primaries. White LSB, Amsterdam, The Netherlands,  January 2011.

 

Partly leucistic Black-headed Gull, moulting to summer (alternate) plumage, showing a partially formed hood. White LSB, Amsterdam, The Netherlands,  March 2011.

 

Partly leucistic Black-headed Gull. White LSB, Amsterdam, The Netherlands,  November 2011. More images can be found here.

 

Albinism

In albinism, the melanin pigment cannot be produced at all, resulting in a completely colorless bird. Remember the remark at the top of this post about skin and eyes only having eumalin? Because an albino bird cannot produce that pigment, its skin and eyes are also colorless. These therefore appear red or pinkish because of the blood that can be seen through the tissue. They are therefore easily distinguishable from leucistic birds, which will always have colored eyes.

Albinos also suffer from a reduced eyesight, making them less likely to survive. This also makes it less likely that birders will encounter such individuals in the field.

Brown

Another form of leucism is the ‘Brown’ abbaration, in which the eumalin pigment (responsible for black, gray, and dark-brown feathers) is reduced. Such feathers are very sensitive to sunlight though and can bleach quickly and strongly, turning these feathers white.

 

Leucistic European Herring Gull (Larus argentatus), brown abbaration. This individual appeared almost completely white in the field, with just some brown patches on the outer primaries and primary coverts, and some dark scapulars. It was not until studying the photos that much more brown markings could be observed. The tail markings for instance is fully present. A very striking and beautiful bird to watch. More images can be seen here. Barneveld waste dump, The Netherlands, October 2011.

 

Source: “Not every white bird is an albino: sense and nonsense about colour aberrations in birds”
Author: Hein van Grouw
Publication: Dutch Birding, vol. 28, no. 2, 2006 (pages 79 – 89)
Link: PDF

New Rings

Dutch bird ringer Frank Majoor is now using a new set of color rings for ringing Black-headed Gulls in The Netherlands: a white ring with two characters separated by a dash (-).

These have been introduced in November this year, after having run out of the usual red rings which have been used between 2004 and 2010.

The color rings are placed on the left leg (tarsus) and should be read upwards. A metal ring is placed on the right leg (tarsus, ringing station ‘Vogeltrekstation Arnhem’).

Used codes are:

• A-A to A-Z
• 0-0 to 9-9
• A-1 to Z-9
• 1-A to 9-Z

More information can be found on Frank’s website (scroll down to ‘codes which have been used’).
Details for sending in observations can be found on www.cr-birding.org.

Old Acquaintance

Return of a 23-Year old Black-headed Gull

Last Sunday (November 13) I did my usual round of checking various locations in and around the city of Leiden, The Netherlands, looking for ringed (banded) gulls. At this time of year, the cities here are full with predominantly Black-headed Gulls and Herring Gulls, while low numbers of Common Gulls are also starting to appear (their number will increase by the time it gets much colder for a longer period of time).

This is now my third winter in which I keep track of the individuals which are present and this winter I again expect a group of about 20 Black-headed Gulls to spend the winter here, spread over 5 or 6 different locations (there will be more of course, but I only keep track of a certain number of locations). They will have arrived from countries such as Sweden, Finland, Germany, Lithuania, Poland, Czech Republic, and Belgium. A small number of Dutch gulls which have not migrated south can also be seen (although the majority will have moved by now).

Some 14 individuals have already returned and one of the highlights was the return of a Dutch Black-headed Gull with ring Arnhem 3431752. It was ringed on June 11, 1988 in Delfzijl harbour, The Netherlands, as a pullus (chick).

13 November 2011, Leiden, The Netherlands

 

My first observation was in January 2010 with my second not until a year later. I was able to observe it 5 times last January after which it once again disappeared. I was therefore not expecting for it to show up so early in the winter and was presently surprised to find out last Sunday that it is still around.

Being ringed such a long time ago, it was fitted with an aluminum ring (placed upside down) which has since become very thin and worn although surprisingly legible.

4 January 2011, Leiden, The Netherlands. Inset: the worn and very thin ring is still very legible (although it doesn’t help that it is placed upside down)

 

The bad news this year is that the ring has moved down to below the hind-toe and is in danger of being lost.

13 November 2011, Leiden, The Netherlands.

 

It would be a shame for this gull to become ring-less, especially since it has reached such an old age (it’s quite exceptional for a Black-headed Gull to reach an age over 20). The local gull ringers have already been informed and we are hoping to recapture this gull soon so that it can be fitted with some longer lasting rings. We are confident that the current ring will last until then, hopefully the gull will stay in the area long enough.

13 November 2011, Leiden, The Netherlands

Moving Forward

Gull behavior part 1: the forward posture

For me, one of the most fascinating aspects of gull watching is observing their behavior. It is a totally enriching experience and it extends the process of just watching an individual to knowing what it is doing and why it is doing it.

As is the case for most other birds, gulls communicate by means of a fixed set of postures and calls. Depending on the context in which they are used, these can have a particular meaning.
These postures and calls are shared by all gull species, although some species have a few postures or calls which are specific for that species only.

In my quest of finding out more about gull communication by studying gulls in the field and by researching various sources of information, I will discuss each type of communication in a series of posts. It will also give me an incentive to go out and record that particular behavior so that I can share it here.

First off: the forward posture.

An adult Black-headed Gull in winter (basic) plumage displaying the forward posture. Leiden, The Netherlands, 10 December 2010

The Forward posture is used in the following situations:

• hostile encounters
• pair formation sequences
• as a response to a bird approaching in flight

The posture is very common in hooded gulls and can be used both on land and in the water. Even though it is used in disputes, it rarely precedes an attack. When used in hostile encounters on land, it often includes running towards an opponent, whereas in a pair formation sequence both gulls move parallel to each other.

The forward posture is related to the oblique posture in which the body is held in a diagonal fashion (to be discussed in a later post); both postures are often alternated.

In his book The Animal in Its World, Niko Tinbergen characterizes this type of behavior as a ‘spacing-out’ display or ‘threat’ display, directed at opponents with the aim to move them away or to stop their advance.

Body position
As the name implies, this posture is all about displaying a forward motion by holding the body roughly horizontal or slightly diagonally with the neck kinked characteristically. The tail can sometimes be spread; the bill is either slightly opened or closed.

A Black-headed Gull in winter (basic) plumage in the forward position with the neck in a characteristic kink. Leiden, The Netherlands, 11 January 2009.

The use of this posture in an aggressive context can be recognized by the carpal joints being raised and the wings lifted from their supporting flank feathers. Lifted wings are an indication that these are ready to be used to strike out with.

An adult Black-headed Gull in summer (alternate) plumage in the forward posture with the carpal joints raised and the wings held slightly away from the body. Leidschendam, The Netherlands, 13 June 2009

A 1st-calendar year Black-headed Gull (right) in a forward posture aimed at an adult Black-headed Gull. The adult responds aggressively by adopting an oblique posture with the wings lifted. Leiderdorp, The Netherlands, 21 February 2010.

A Black-headed Gull in a forward posture during a meeting ceremony with a mate. The tail is slightly spread. Leiden, The Netherlands, 10 December 2010.

Forward posture in other gull species (in alphabetical order):

• Black-headed Gull (Chroicocephalus ridibundus). See above description and photos.
  
• Black-legged Kittiwake (Rissa tridactyla). No information available.
• Caspian Gull (Larus cachinnans). Forward posture is held briefly after the throw-back posture as part of the long-call.
• Common Gull (Larus canus). Similar to the hunched posture and apparently poorly ritualized.
• Franklin’s Gull (Larus pipixcan). No information available, however the long-call display apparently can transform into a posture much like the forward posture.
• Glaucous Gull (Larus hyperboreus). No information available.
• Great Black-backed Gull (Larus marinus). Similar to that of Black-headed Gull. Combined with a rush at the opponent resulting in chasing it away or fighting with it vigorously. May be followed by an arch posture when opponent does not flee. Only used outside of the breeding season.
  

  Two first-calendar year Great Black-backed Gull approach an opponent while adopting the forward posture. IJmuiden, The Netherlands, 16 October 2011.

  

  Sub-adult Great Black-backed Gull fending off oponents from its European Flounder by adopting the forward posture. IJmuiden, The Netherlands, 16 October 2011

• Herring Gull (Larus argentatus). No information available.
  
• Ivory Gull (Pagophila eburnea). Forward posture similar to that of Black-headed Gull is superficially represented by the throw-forward posture.
• Laughing Gull (Larus atricilla). No information available, however the long-call display apparently can transform into a posture much like the forward posture.
• Lesser Black-backed Gull (Larus fuscus). Forward posture similar to that of Black-headed Gull used briefly following final oblique posture as part of the long-call display.
• Little Gull (Hydrocoloeus minutus). The forward posture is apparently not used by this species; its functionality is displayed by adopting the oblique posture followed by a vertical posture.
  
• Mediterranean Gull (Ichthyaetus melanocephalus). The typical forward posture is apparently not used by the Mediterranean Gull although it has been observed as part of pair-bonding behavior.
• Sabine’s Gull (Larus sabini). Forward posture used as end sequence of long-call and directed towards distant opponents in the air or on the ground.
• Slender-billed Gull (Larus genei). The forward posture has not been recorded for this species.
• Yellow-legged Gull (Larus michahellis). The forward posture is held briefly after the throw-back posture as part of the long-call.

Sources used:

The Animal in Its World – Niko Tinbergen, third printing 1975

Birds of the Western Palearctic interactive

The Odd One Out

It is the beginning of November, autumn has only just started and we still have a long winter ahead of us. Here in Europe, adult and fledged gulls have left their breeding grounds roughly around July and have since fanned out in various directions. Some individuals have already traveled hundreds of kilometers to spend the winter far south. Young gulls are supposed to take care of themselves and adults have split with their mates to become individuals again.

In the latter stages of the breeding season, gulls have started their moult to basic (non-breeding) plumage. Distinct colouration of legs, bills, eye rings and hoods — used as signals of good health in order to attract a mate — have since started to fade because their function is not required anymore. Not until the beginning of next year will these colours return and feathers will be replaced during the moult around that same time so that the to alternate (breeding) plumage is acquired once again.

Not so though for all individuals.

Every now and again you come across an individual who is the exception to the rule.

Today I saw the first Black-headed Gull with a strong outline of its brown hood:

Adult Black-headed Gull with the outline of the hood clearly visible. Leiden, The Netherlands, 4 November 2011.

 

Black-headed Gulls at this time of year are supposed to have no hood at all, but instead a white head with two black ear spots and faint bands going across the head, connecting both ear spots and both eyes.

Adult Black-headed Gull in typical basic (non-breeding) plumage. Leiden, The Netherlands, 30 October 2010.

 

Those individuals who moult their hood early apparently do so every year. What is interesting though is that their moult takes place over a much longer period of time than for those individuals who acquire their full hood during the regular moult stage. Those who have a normal moult do so very quickly, up to 10 – 15% a day. This means that a full hood can be acquired in around a week. The individuals that I have seen with early head moult (see examples below) took weeks before their hood was anywhere near completion.

I have a feeling that the individual I saw today is the same one that I observed at the same time and at the same location last year. Black-headed Gulls have a tendency to spend the winter at the same location each year, so the odds are in favour that this is the same gull (although it cannot be proven without other distinctive characteristics or a ring around its leg).

The following images are of the individual photographed last year at the same location (Leiden, The Netherlands):

Leiden, The Netherlands, 31 October 2010.

 

Leiden, The Netherlands, 6 November 2010.

 

Leiden, The Netherlands, 20 November 2010.

 

Some more examples:

Leiden, The Netherlands, 28 November 2010. See this page for a full set of images of this individual in various plumages.

 

Leiden, The Netherlands, 30 November 2010.

 

Leiden, The Netherlands, 22 January, 2011.

For more information about head moult in Black-headed Gulls, visit the site of Frank Majoor.