9-J, juvenile lesser black-backed gull ("Larus fuscus")

16 November 2025

NOVA FALCONS, A COMPANY SPECIALISING IN ENVIRONMENTAL STUDIES, WILDLIFE MANAGEMENT AND OTHER ENVIRONMENTAL SERVICES

On 15 October, our technician Alba Moreno spotted a seagull with first-year juvenile plumage (i.e. born this year) wearing PVC rings. This type of marking is designed to be read from a distance, i.e. without having to catch the bird. Through the code written in ascending vertical letters on the green ring (9-J), in combination with the plain blue ring on the other leg, it was possible to locate the project responsible.

First-year juvenile sooty gull; photograph by Alba Moreno.

At first glance, it may be difficult to identify the species, as due to its age (first-year juvenile), it closely resembles other species of gull, especially the one most commonly found in the Pitiusas: the yellow-legged gull. Furthermore, the yellow-legged gull is a nesting species in Ibiza and Formentera, unlike the lesser black-backed gull.

First-year juvenile yellow-legged gull (Larus Michahellis).

Although identifying juveniles by their plumage is something only experts can do, adult specimens can be distinguished with relative ease once you have trained your eye a little. The lesser black-backed gull, as its name suggests, has a darker mantle, but otherwise, they can look the same: both species have very similar-looking beaks and legs, and broadly speaking, they share the same white body colour distribution. There is a slight difference in size, with yellow-legged gulls being larger, but it is true that there can be overlap and this is not a particularly useful characteristic. The key, without a doubt, is to look at the ‘grey’ areas on the yellow-legged gull, which we can see every day in the Pitiusas: if a specimen has a colour closer to black than grey, we are probably looking at a lesser black-backed gull.

Adult specimen of the yellow-legged gull, our local gull par excellence.

Adult specimen of a lesser black-backed gull. Note how the colouring is much darker on the mantle and coverts than on the yellow-legged gull, which is clearly grey in colour.

The lesser black-backed gull is an occasional winter visitor to the Pitiusas Islands, meaning that it is not uncommon to see one or two specimens from time to time, but they do not form flocks, nor are they usually seen on a daily basis. It was therefore a pleasant surprise to see that this was not what might initially have been thought to be the most likely species. This also highlights the fact that there are probably more lesser black-backed gulls than it might seem, as there are also juvenile specimens among the winter visitors that are difficult to detect.

Furthermore, its identification provided us with another curious piece of information: although there are breeding areas for this species on the Iberian Peninsula, the closest to our islands being the Ebro Delta, it turned out to be a specimen born in the Netherlands. It was ringed as a chick on 4-7-2025 in Vlissingen-Oost (Sloehaven), Zeeland, Netherlands. In other words, this juvenile, barely a few months old, has already travelled 1,400 km from its breeding colony.

Area of origin (Netherlands) and sighting (Ibiza) of 9-J.

This type of monitoring helps us to better understand the dispersal processes of species. If you ever see a bird ringed with PVC tags, try to take a photo where the code is clearly visible. With this code, either through a group or company that carries out ornithological work, or through the Doñana Biological Station website, you can contribute to reporting the information to the project responsible for its tagging. This type of tagging only makes sense if readings are received, which is why they are easily readable from a distance, but it is true that the general public is not usually aware of how important it is to report such sightings, or how to do so if they wish to report them.

First-year juvenile sooty gull; photograph by Alba Moreno.