Egg predation by an adult Lesser Black-backed Gull – 20140519

The life of a young Lesser Black-backed Gull or Herring Gull is full of hazards and many won’t make it past the first few months.

Some don’t even get the chance to be born: egg stealing and consummation (egg predation) by adult gulls is a regular occurrence in colonies of the large gull species.

These individuals are usually highly specialized birds. In his thesis “A HISTORICAL ECOLOGY OF TWO CLOSELY RELATED GULL SPECIES“, Dutch gull researcher Kees Camphuysen writes:

“…Herring Gulls would seem the most important egg-stealing species considering the data presented above. This may be misleading. Some highly specialised Herring Gulls were monitored feeding on eggs for part of the breeding cycle. Only six pairs of Herring Gulls were found to have consumed 79% of the 308 eggs found in our prey samples.

Lesser Black-backed Gulls practiced egg-stealing frequently, but apparently more opportunistically. More importantly, they did not bring many eggs back to their own nest, but rather devoured them at clubs or at the raided nest itself. We did not encounter specialised Lesser Black-backed Gulls with more than a few eggshells as prey remains around their own nest.

Peaks in egg predation by the two species are c. two weeks apart suggesting that this form of cannibalism is triggered by the laying activities of conspecifics. The overall mean date of egg-stealing was 1 June in the Lesser Black-backed Gulls and 18 May in the Herring Gull, which is 19 respectively 11 days after the mean laying date of each species. This gap is probably wider than in reality, as a result of delays in prey sample collecting (on extremely busy days, sampling was sometimes skipped a visit or two if the breeding status of that nest was not expected to change meanwhile).”

I witnessed such an event during a visit in the gull colony of IJmuiden (Forteiland), the Netherlands earlier this week.

It’s perhaps not one of the nicer types of gull behaviour to observe but it is very much a fact of life in a gull colony. On a positive note: it was the only instance of egg predation that we came across that day.

The photos show how the bird walks away with the egg immediately after stealing it, making a short flight and returning to a spot only a few meters from the place where the egg was stolen, calling while standing over the egg and subsequently breaking the egg open and eating its contents.

All photos were taken on 19 May 2014.

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3 thoughts on “Egg predation by an adult Lesser Black-backed Gull – 20140519

  1. I saw this once in real life, with Black-headed Gulls.

    I think that it’s more disturbing when they start pecking each other’s chicks to death. I’m not sure that’s for the purpose of eating them – it seems as though the adult gulls just become enraged by another chick wandering onto their territory.

    Have you ever heard that gulls will sometimes steal a neighbour’s egg – but then get it confused with their own eggs, so end up placing it in the nest and incubating it? I read about that somewhere. Not sure how widespread that behaviour is.

    • Yes, in large gull species, young gulls are a food source for specialized gulls. This happens especially when regular food sources are scarce. In smaller gull species (such as Black-headed Gull), pecking young gulls only happens when they wander into their territory.

      I have not heard of gulls getting confused by the eggs that they steal, I would be interested to see the source of that reference.

      • It was just something I read on the internet a few months ago (I’m always reading random gull stuff and clicking through to more gull stuff, which I don’t bookmark!). I don’t think that it was in a peer-reviewed paper, or anything like that. It may have just been someone’s random observation on a blog post or Youtube comment. I’ve tried to google for ‘gull adopts stolen egg’, but I can’t find anything now. I was actually hoping that you might have known something about it… 🙂

        I do wonder why the cannibalistic gulls don’t get immediately ganged-up on and killed by the other parent birds. Considering how aggressive gulls can sometimes be in defence of their eggs and chicks, it’s strange that they seem to tolerate this within their own colonies.

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