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Thread subject: Wing Loading
Name Date Message
Anne 06/30/05 07:04 am Does anyone know anything about wing loading please? I remember my tutor saying something about raptors having poor wing loading, and that is the reason why eagles and vultures have to soar to great heights to catch a thermal, and why they gather at narrow straits such as Gibralter and the Bosphorus to migrate across the sea. They cannot fly by flapping for long.

But I'm sure he said something about ospreys being different, and that is why they can migrate over water (such as the bay of Biscay) for longer distances. I wish I could find my notes of that lecture!
Celeste 06/30/05 07:23 am Anne in searching the internet I found the following:

Ospreys are broad-frontal migrants at high latitudes, but tend to follow leading lines farther south. Unlike many raptors, Ospreys do not depend on soaring on updrafts and thermals to complete their migratory journeys. The species is willing to cross large bodies of water and other areas of inhospitable habitat like deserts. Ospreys will fly early and late in the day when thermals are either weak or non-existent.

Another point I found interesting is the following:

"Like many other raptors, Ospreys do not deposit large amounts of fat prior to migration. Because they tend to expend a lot of energy on migration, they often refuel en route at places where prey is abundant and available. Ospreys are sometimes seen carrying fish with them while migrating, something that is rarely observed in other migrating raptors."

The Rutland Site provided this..........
"This was discussed at the Osprey Project Steering Committee meeting on Thursday 28th October 1999 and the concensus of opinion was that Ospreys use thermals very little, if at all. Roy Dennis pointed out that when Ospreys are observed at raptor migration watch points such as Gibraltar they are seen flying directly through and not joining other thermalling birds of prey. Recall that Ospreys migrate on a broad front rather than using particular routes where the thermals are good. Our observations of night-time crossings of water-bodies indicate that they are not using thermals then.

I noted the discussion on whether or not Ospreys use thermals. Based on my observations of migrants in Hampshire I have found that Ospreys, and migrant Buzzards, harriers etc., often stay low when moving in/out over the sea if there is a headwind. If there is a tailwind they often gain considerable height by soaring before closing their tail and setting their wings into a glide position and just letting the wind push them along. "

Amazing isn't it?!

Anne 06/30/05 07:37 am Oh yes - fascinating, thanks for that. How all these different species have evolved so differently - using different tactics for feeding, migration etc. - its mind blowing really.
Marie 06/30/05 09:51 am Well that is very interesrting info Celeste...I know out this way I have seen osprey using thermals just for play.........a small speck in the sky has turned out to be an osprey when it finally lands down on its nest.......this would be on a bright sunny day when there are thermals off the land.

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Tom Throwe
Last modified: Sat Feb 18, 2006