Kleptoparasitic behavior in Black-headed Gulls towards Sanderlings – 20140119

While at the beach of Katwijk aan Zee on Sunday, I observed gull behavior that I had never seen before nor was aware of: Black-headed Gulls Chroicocephalus ridibundus stealing food from Sanderlings Calidris alba by chasing and harassing them — a process known as kleptoparasitism (see Wiki).

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

Hundreds of Sanderlings were fouraging in small groups at various places along the water edge. Among them, several Black-headed Gulls of all ages had gathered and were mostly fouraging themselves, minding their own business.

At various moments though, Black-headed Gulls could be seen chasing a Sanderling as soon as they spotted it with food.

Most of the time the chase was done by a single gull but at one point I saw one Sanderling being chased by 3 individuals.

Even though the Sanderlings were much more maneuverable because of their smaller size and tried to out-turn the much larger Black-headed Gulls, the gulls managed to keep up with them in most instances.

Sometimes the chase was successful, sometimes it wasn’t.

Some chases only lasted a brief moment while some Sanderlings were chased relentlessly, not prepared to give up their food.

It must have been quite a harrowing experience for such a small bird (weighing around 50 grams) to be bullied by such a large gull.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

The behavior was not restricted to adults only: I was surprised to see first-year Black-headed Gulls chasing Sanderlings too. Katwijk aan Zee, The Netherlands, 19 January 2014.

The behavior was not restricted to adults only: I was surprised to see first-year Black-headed Gulls chasing Sanderlings too. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

An adult Black-headed Gull chasing a Sanderling. Katwijk aan Zee, The Netherlands, 19 January 2014.

The prey: a Sanderling with food. Katwijk aan Zee, The Netherlands, 19 January 2014.

The prey: a Sanderling with food. Katwijk aan Zee, The Netherlands, 19 January 2014.

How common is cleptoparasistism in Black-headed Gulls?

The only example of cleptoparasitic behavior in Black-headed Gulls that I was aware of was towards Lapwings Vanellus vanellus and Golden Plovers Pluvialis apricaria after having read Gulls and Plovers — The ecology and behaviour of mixed-species feeding groups (1975) some time ago.

The behavior towards terns is described in “Kleptoparasitism of Sandwich Terns Sterna sandvicensis by Black-headed Gulls Larus ridibundus” (1977) and also in Living with gulls: the consequences for Sandwich Terns of breeding in association with Black-headed gulls (2001)

Birds of the Western Palearctic (BWPi, interactive version) states that Black-headed Gulls are “food-pirates and scavengers’ but surprisingly does not mention cleptoparasitism as part of the feeding behavior for this species of gull.

Why invest in this behavior?

While observing the gulls chasing the Sanderlings I was wondering how investing so much energy in chasing a small bird carrying such a small amount of food can be beneficial over finding the food themselves? To me it looked like there wasn’t a shortage of food around: food actually seemed to be in abundance on the beach.

I couldn’t see a clear need therefore to resort to this type of behavior.

Having said that, the birds that were feeding on the beach (the Sanderlings as well as various species of gulls) seemed to prefer specific areas instead of spreading out evenly over the available space. What was noticeable with the gulls especially was that each time they were disturbed by beach goers the gulls retreated onto the water some 20 meters and more from the beach, waiting for the moment when it would be safe again to return to the exact same spot.

That certainly limited the opportunities of obtaining food.

Competition between gull species and differences in hierarchy within a species (adults versus non-adults and males versus females) may also play a part in food availability.

I found it very interesting to observe this behavior therefore and will certainly make an effort to study it in more detail when I come across it again.

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5 thoughts on “Kleptoparasitic behavior in Black-headed Gulls towards Sanderlings – 20140119

  1. I’m trying to think now – I’m pretty sure that I’ve seen BHGs chasing smaller birds for food in the past. Feral pigeons, maybe? Or Starlings? Can’t say for certain though – it may have been the bigger species.

    But have you ever noticed how it seems to be in their nature for gulls to give chase? There can be a big pile of food on the ground, but it’s really common for a gull to grab a small piece of something, only to be immediately chased by two or three others – despite there being loads of stuff still there for the taking. It’s as though seeing another bird with a food item will ‘set them off’…

    • Hi Phil,

      Yes, gulls are indeed known for chasing each other but similar to chasing Sanderlings I think that it is all about competition and about finding the most efficient way in getting to the food. Even a huge pile of bread is no guarantee that each individual is able to take their pick. Most of it will be taken by the most dominant individuals while the more timid ones are left to wait their turn (which might not come).
      So it could well be that those lower in the picking order are the ones that give chase but maybe only if they think that they will be successful. Will a first-year bird give chase to an adult, dominant male? Or only when accompanied by other adults?
      Without being able to individually identify each bird in a group and knowing their characters we can only speculate.

      As far as Black-headed Gulls chasing other, smaller bird species is concerned, I am surprised to find so few references and would love to come across more studies.

      • That’s the tricky thing about studying gulls in a social context. They tend to lack distinguishing features – and they change their plumage often. Unless they’re like your 29th year buddy, with his thin, patchy, head feathers, or you have a certain gull with a missing leg/eye, or a damaged beak, or whatever – or you have a ‘special friend’ that comes to visit you regularly. They don’t really stand apart from the crowd otherwise.

        I suppose that you’d really need to catch and tag most of the flock in order to be able to draw any meaningful conclusions from your observations…

  2. excellent observation regarding a most probably not well studied behaviour. I have not seen this behaviour in large gulls. Did it cross your mind that the BHG may not be able to open the ensis shells themselves and “use” the sanderlings for that purpose?

    • Hi Jan,

      You make a good point.
      It is certainly true that the Black-headed Gulls were in direct competition with the Sanderlings by not being able to access shell food in a way that Herring Gulls can.
      The Black-headed Gulls were foraging in the soft sand similar to the Sanderlings and it therefore makes sense that they used them as a target.

      Now that I think about it, it is interesting to note that the Common Gulls (Larus canus) that were present displayed a completely different behavior. They are well known for chasing other gulls, but instead of chasing the Black-headed Gulls or the Sanderlings, they were predominantly foraging in the surf.

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