As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Thursday, 10 November 2016

Why some hummingbirds choose to balloon up before flying south

Date: October 13, 2016
Source: University of Toronto

New U of T Scarborough research has found adult ruby-throated hummingbirds choose to pack on significant weight in the four days before their long migratory flights south for the winter.

"Many different birds fatten up before they migrate, but we wanted to know what specific strategies hummingbirds use to fuel up prior to migration," says associate professor Ken Welch.

"It turns out that individual hummingbirds make individual decisions -- some fatten up for long flights, while others stop and fuel along the way."
Welch and masters student Lily Hou developed a unique system to track and weigh hummingbirds in the wild before migration using radio frequency identification tags. Each bird had a microchip and were weighed each time they landed on a balance attached to the feeder.

They found hummingbirds that fatten up spent more time at feeders in order to gain weight rapidly, in some cases putting on as much as 35-40 per cent of their body mass in the four days before migration. They also found that no juvenile birds were fattening meaning that those choosing to fatten up had made the migratory trip at least once.

"This suggests fattening could be a learned behaviour and it's based on experience," says Welch. He adds the findings add to a growing body of research suggesting that for some birds their pre-migration strategies are affected by age and experience.

Birds generally use two strategies when it comes to preparing for migration. One prioritizes fattening to allow a more direct flight in order arrive at the wintering grounds quickly. The other involves shorter flights, stopping and feeding along the way.

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