Monday, 25 April 2016


UV and the passage of the Sahara

So we think that UV has commenced his return migration. His first challenge is to traverse the western desert – a 2000 km flight to reach the straits of Gibraltar. We tend to think of this as a hazardous route, and for us it would be. But for birds – not so much...

22nd April 2016: UV sets out from Senegal, catching a few thermals on the way.  (Data: Forestry Commission England) 

There are few sizeable predators, and even fewer that would be capable of taking on an osprey. There are almost no invisible overhead cables to trap the inattentive; no mad fat bastards with guns to shoot at them; no speeding vehicles to collide with them. The skies are clear and visibility is good. It's just a matter of flying.

Of course there are no fish and precious little water in a desert – but an adult osprey in the early stages of migration does not require these things. Before leaving Senegal, UV will have bulked up, laying down fat reserves as fuel for the coming journey. And as he flies northwards, his body deploys Evolution's secret weapon for long-distance migration... “ß-oxidation.”

This is part of a three-stage process whereby lipids (stored fat) are converted into energy to power UV's flight muscles. And as a by-product, metabolic water is released at the cellular level. The numbers seem like a conjuring trick: 110g of water is produced for each 100g of fat consumed! (Okay, some other stuff is going on here as well, but it's still a remarkable adaptation.)

This biological miracle is the key to long-distance bird migration: the longer and harder you fly, the more water you get!