herring gull feeding behaviour

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The behaviour of seagulls whilst feeding:

The behaviour of seagulls whilst feeding By Ashleigh Weir

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With many becoming totally urbanised, feeding and even nesting in cities They are opportunistic omnivores that normally would feed on aquatic pray but since the build up of human rubbish prefer to scavenge. Or better known as seagulls, are sea birds found along the coast of the UK and generally live in large colonies nesting along cliffs. Herring gulls ( Larus argentatus )

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In this study some of the behaviours of the gulls was observed whilst feeding. (Video captured on the 28 th of February 2011)

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First we see the gulls circling the area in which they want to land

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Next you see one brave bird landing and being quickly followed by others.

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Feeding its self is a chaotic time with only a loose hierarchy being observed based on size and aggression of the individual. The age of the bird also has an affect on its success when feeding as studied by Verbeek 1977, the older birds have more success when foraging so the younger individuals will steal or scavenge food instead of trying to catch it themselves.

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The Hawk-Dove game is a name given to the behaviour seen in two individuals when competing for a resource (e.g. Food or a nesting site). During feeding a hawk-dove, game interaction can be seen where one bird goes to fight another for a piece of food (the hawk) and the other backs off choosing not to engage (the dove). Both behaviours have both advantages and disadvantages which we will explore now.

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Choosing to behave as a dove: This behaviour was brought on by the aggressive challenging behaviour of the ‘hawk’ and was chosen as the best behaviour to adopt by the bird because the benefit of the food may not have outweighed the fighting and potential injury. The gulls might choose to change strategies from dove and hawk depending on their age and size and experience with dealing with other birds. They might also change behaviours if food is scarce and they are hungry. Choosing to be a dove means you have the short term disadvantage of no food but the long term advantage of not sustaining an injury or death and therefore would be advantageous over hawk in many situations.

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Choosing to behave as a hawk: This behaviour was brought on by competition for a resource, in this case food. This behaviour of challenging another for food generally pays off as the other animal will either not engage in the fight and you get the food (like in this case) or you are larger and stronger than them and so get the food in the end. However in other cases you will fight and loose ending in a cost. Therefore the hawk strategy is best adopted by older larger birds who are more likely to win. This strategy therefore relies on the hawk being bigger and stronger than the other they engage in fighting or they loose and reduce their fitness potentially reducing their reproduction rates or even survival.

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Aggression or being the hawk has many advantages as you gain the most food, best territories and the best females therefore being the fittest. However these do come at a cost with an increased risk of injury, more energy expenditure and increased exposure to predators. So what is the best strategy?

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In our case one bird assesses the situation and decides not to fight choosing to be a dove. Reducing the chance of injury but still establishing a hierarchy. Through experiments it has now been shown that many species have evolved to play the hawk-dove-assessor game where they size each other up using non aggressive means first then decide what role to play.

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Many other gull species show this behaviour of hawk-dove-assessor game because they live and feed in such large colonies they must. It is a behavioural mechanism that allows the population to become stable by allowing each individual the chance to assess the fitness of others honestly before having to engage into a fight. This means less of the population must sustain a injury to share out resources.

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Once the food supply has ended and there is no more food available most birds leave. It only takes one bird to get spooked and all the others will fly too .

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To find out more about herring gulls here are some resources: http://www.bbc.co.uk/nature/life/Herring_Gull The Herring Gull's World: Study of the Social Behaviour of Birds by Niko Tinbergen.

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