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.
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.
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.
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.
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-backed, I focused on specific characteristics. The primary pattern for starters did seem to match that of a graellsii:
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 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 sink in. 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.