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.

Tuesday, 30 August 2016

City centre gulls could help plan drone flight paths

 The issue of gulls in cities is an interesting one, as populations of Herring Gulls and Lesser Black-backed Bulls are declining in many rural areas, while increasing in many urban locations.

The reasons are likely multiple, among them easy access to nesting sites and food, and a learned tolerance of humans. However, in our recently published study, we raised the possibility that ease of flight might also make city centres an attractive option for these birds.

Turbulant skies
As terrestrial animals, it can be difficult for humans to imagine what it is like to travel in a medium that is also moving. If you swim in a pool alone, it feels easier to slip through the water because it hasn't been churned up by another swimmer. This is just small-scale turbulence: add on top of this how it feels to swim in the sea, where the tide can pull you back as you try to return to the shore, and you will begin to understand what it is like to be a bird.

Now imagine that you have to swim through the sea to get to work every day. Sometimes the currents would be with you, sometimes they would be against you, this and the choppiness of the water will have a huge effect on how hard you have to work. If you had to do this every day, you would get pretty good at predicting the sea state and current direction. Flying animals face this all the time: the air is hardly ever still and this has a profound effect on flight behaviour.

In our study, we looked at how gulls use the rising air generated by buildings to fly without flapping. Using the seaside city of Swansea as our research location, we found that gulls actually alter their flight paths in certain wind conditions, to take advantage of updraughts occurring around a line of hotels bordering the bay.

Such energy-saving strategies are already well-recognised in birds that are undertaking their vast annual migrations, but are less well-studied for birds moving around on a daily basis.

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