Avian pecking order is determined by their size and weight, a study of garden bird feeders has found.

A study by Exeter University has found prize bird food, like easy-to-eat sunflower hearts, tend to be eaten up by the largest birds.

Smaller birds, including bluetits and coal tits, are lower in the pecking order so are forced to eat lower quality sunflower seeds, which take much longer to position in their beak, crack open the shell and remove the hull.

blue tit

Despite being just two-thirds of an ounce (18g) lighter than a sparrow or greenfinch, these smaller birds are forced to peck faster and fly away more quickly from feeders.

They were the 'losers' when birds competed for food, being forced away by larger, dominant birds. 

Professor Jon Blount, a senior author of the study from the Centre for Ecology and Conservation at the University of Exeter, said: 'Bird feeders create a concentrated food source which can result in more quarrels between individuals of different species, which we predicted would lead to the formation of a dominance hierarchy.

'Our findings show that larger, heavier species get better access to food - so if the aim of bird feeders is to benefit all species, we need to investigate ways to achieve this, such as different mixes of foods and feeder designs.' 

It is estimated that three-quarters of British homes leave out food for wild birds. 

Researchers say smaller birds could be helped with specialist foods they enjoy, such as peanuts, or with bird feeders designed for smaller birds.

Working with the British Trust for Ornithology, the scientists examined the behaviour of 10 types of perching birds at feeders over 29 days. 

They found the most dominant birds were bigger, including sparrows, greenfinches and nuthatches, and won the best access to popular sunflower hearts. 

nuthatch

Less dominant smaller birds, including coal tits, dunnocks and chaffinches, more often ended up with harder-to-eat black sunflower seeds.

The study, published in the journal PLOS One, states: 'Interestingly, for low ranking species the energetic benefit of foraging on sunflower hearts was apparently outweighed by the potential costs of aggressive interactions.' 

Kate Plummer, joint first author of the study from the British Ornithological Trust, said: 'With more and more people feeding the birds in their gardens it is more important than ever that we understand any implications this might have for the birds themselves.'

WHAT ARE THE MOST DOMINANT GARDEN BIRDS?

This is a list showing the order of dominance of different species and their weight (in g).

1) House Sparrow (27.3g) 

2) Greenfinch (27.7g)

3)Nuthatch (22.1g)

4) Robin (19g)

5) Goldfinch (15.8g)

6) Great tit (18.6g)

7) Dunnock (21.2g)

8) Chaffinch (21.8g)

9) Blue tit (10.9g)

10) Coal tit (9.1g)

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