Fattening swallows prior to migration

THERE’S an interesting paper in the current edition of the journal Ringing & Migration.

In ‘Fattening Strategies of British & Irish Barn Swallows prior to Autumn Migration’ Lisette Coiffait, Robert Robinson, Jacquie Clark and Bridget Griffin examine the weights and ‘fat scores’ of 543 swallows caught at 35 locations in Britain and six in Ireland. Prior to migration, swallows spend their nights in communal roosts, close to which they can be caught using mist-nets. Each bird is ringed and a range of measurements taken.

Small birds must fatten up before migrating; they need extra fuel for the journey. At this time of year, most of the day is spent feeding and there’s little time left for anything else. The only option for most avian travellers is to forego their beauty sleep and ‘fly by night’. It’s safer to do this in any case; an overweight bird is sluggish in the air. Less able to wriggle out of danger, it’s a sitting duck for predators.