Bird Waves

[simon colenutt]

Here is a question that has perplexed me for ages. When seawatching why do you have these lulls and then suddenly waves of birds pass, for example, you can be watching a scoter passage with hundreds of birds passing, then all stops, an hour later flocks begin to pass again for another 30 mins and so on. What causes these waves- any ideas???

Maybe I had to much whisky last night!!!
:h?:

[Andrew Whitehouse]

I've often wondered too, Simon. I suppose as most seabirds are gregarious they're going to be distributed in a 'patchy' fashion (both in time and space, as it were), so that might partly explain things. It's often noticeable that you get rushes before and after rain showers. I think a lot of birds put down on the sea when there's heavy rain, so a 'backlog' builds up.

It's an amazing thing to see whatever causes it - almost like a 'seabird tap' being switched on and off. Shearwaters, Kittiwakes and Little Auks are particularly prone to this sort of stop-start movement in my experience.

[Michael Frankis]

I've noticed this as well, tho' it's hard to tell from random timing. It would perhaps be more peculiar if they flew past at a completely steady rate.

Michael

[Nancy]

My theory is that they fly in very large circles, perhaps following food sources carried by water currents. I have actually seen this happening while watching shearwaters from a high clifftop. The birds went past in a constant stream, flying from left to right, for about 8 to 10 minutes then stopped suddenly. When I put the scope onto the distant horizon I could just discern a steady stream of similiar birds flying from right to left. I didn't wait long enough to find out if they came back close to shore again.

[Rob Smallwood]

Nancy is right - many seabirds feed in this fashion although here in Britain we are more often watching passage birds that do not linger as long.
I believe that British birds published an article on this sort of movement illustrated by birds seen of the South-west coast of Britain, illustrated by mutiple sightings of a rare seeabird moving with commoner ones - but I can't remember the details !