Discussion by: Vorlund
I observed some interesting behaviour among seabirds some while ago while on a cruise holiday.
The ship pulled out early evening in twilight and the water was illuminated on each side by lights from the ship. A flock of gulls which had been perched on the roof of a nearby building followed the ship out to catch the fish that were attracted to the lights. Now this predation wasn't a random free for all from all directions. The birds flew alongside the boat from stern to prow catching fish and then circled back a little way out to avoid other birds coming upstream to feed and then joining on again at the back.
The interesting point for me is that by flying from stern to prow, the speed of the bird relative to the boat is slow and so they have more time to select and catch fish. The return flight in the opposite direction, however, means the time they spend away from the catch is relatively much shorter. It also means (dependent to some degree on wind direction) that they expend less effort in unproductive flying so the whole process is potentially more efficient.
Here is my question, Is this an evolved behaviour? Cruise ships haven't been around very long compared to the development of birds or is it reasoned behaviour? That is to say, are the birds capable of working out that this flight pattern is more efficient? Or is it simply that the fish following the boat can be stalked from behind more readily or is there some other factor?
Does anyone have any thoughts?