July 8, 2016
UEA research reveals why males outnumber females in bird world
Female birds 'fly the nest' from sparsely populated breeding sites leaving behind small groups of lonely males - according to new research from the University of East Anglia.
Research published today in the Journal of Animal Ecology shows for the first time the causes of skewed sex ratios among small and declining bird populations.
The findings reveal how female birds are thought to be choosing busier breeding locations - where habitat is often better, males are more abundant, and the ratio of males to females is more equal.
Lead researcher Prof Jenny Gill, from UEA's School of Biological Sciences, said: "Many migratory bird populations are declining and very small local populations are becoming more common.
"If females prefer places where males are more abundant, small populations are likely to decline even faster.
"However, the unpaired males will continue singing throughout the breeding season in a bid to find a mate, and so we may be underestimating declines in these small populations. We wanted to find out whether this was happening."
The research team used British Trust for Ornithology (BTO) ringing data to explore the extent, causes and consequences of varying sex ratios in breeding populations of willow warblers (Phylloscopus trochilus) across the UK.
Around 8,000 birds were surveyed from 34 sites over 18 years.