Image credit: Jill Pakenham / BTO
The pecking order of garden birds is determined by their size and weight, new research shows.
In a study of bird feeders, researchers from the University of Exeter and the British Trust for Ornithology (BTO) found larger species like House Sparrows and Greenfinches monopolised the best food and spent longer feeding than smaller birds such as Blue Tits and Coal Tits, who fed quickly and on lower value food.
The researchers examined competitive interactions amongst ten species of garden birds that came to feeders containing a high-value food, such as sunflower hearts (husk off), and a lower value food such as black sunflower seeds (husk on). They found a clearly defined pecking order, with larger bodied birds dominating the higher value foods, leaving the lower value foods to the smaller birds.
They then ranked each species in order of dominance by recording any interaction between two individuals that resulted in one retreating from the food source, with the bird that stayed being classified as the more dominant individual.
Though the results do not show the ten species in exact weight order (see table below), there is a strong correlation between weight and dominance. The two heaviest birds (based on average body weight) were rated most dominant – House Sparrow (27.3g) and Greenfinch (27.7g) – while the two lightest – Blue Tit (10.9g) and Coal Tit (9.1g) – were bottom of the list.
Senior author, Professor Jon Blount of the Centre for Ecology and Conservation on the University of Exeter’s Penryn Campus, said, “Bird feeding has become increasingly popular in the UK and throughout much of the world in recent decades, however, its impacts are still poorly understood. 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.”
He added, “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.”
Kate Plummer, of the BTO and joint first author, commented, “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. We know that during harsh weather the foods put out by homeowners can offer a lifeline but outside of this the benefits might be more subtle, so it is interesting that our findings are less straightforward and that more work needs to be done to fully understand garden bird feeding.”
The paper, “Effects of supplementary feeding on interspecific dominance hierarchies in garden birds” is published in the journal PLOS ONE and will be available to read at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0202152.