Flying Low

[sar]

I have noticed a lot of birds flying very low. Just above the ground. Is this because the thermals are poor or is the snowy ground causing them to be confused as to their height off the ground? Or is there another reason.

[nigel_b]

I doubt it is thermals (I fly R/C gliders). However there is a ground effect. This from the net:

Ground effect flying, in birds, is flying less than a wingspan from the ground, usually over water.

Flying this low takes advantage of an aerodynamic effect that reduces drag and makes cruising particularly easy: in ordinary flight, air tries to move from below the wing to above the wing to equalize pressure, creating vortices of air currents that trail behind the wing, decreasing lift and creating drag. When the wing is close to the ground, this effect is greatly reduced.

While birds often take advantage of ground effect, aircraft have also been designed to exploit the energy savings of reduced drag.

[thebeard]

the lack of food may be causing them to looka bit closer perhaps? i don't really know!

[Picidae]

Originally Posted by thebeard

the lack of food may be causing them to looka bit closer perhaps? i don't really know!

I'd imagine this was a large part of it - depends on the species of birds too of course! With the ground frozen and food disappearing fast from hedgerows, just digging around in the ground is more time consuming and energy consuming. Wind chill is also a big factor, obviously, as Nigel points out, reducing air drag conserves energy but also it's probably marginally warmer for them! There may be, conjecture on my part, another reason to do with predation - perhaps they are less visible and thus less vulnerable to aerial attack against a blanket of snow by flying low (ie. narrower FOV for hunting BOP)

[NicolaB]

I've especially noticed a lot of songthrushes doing this lately, unfortunately across roads Have had to brake hard on a number of occasions this week to miss them. I expect the cold weather is driving them to desperate measures, as roadside verges are the only places without snow round here at the moment.