Mixed formation waders/geese, south Sweden April (1 Viewer)

I saw what I thought was a flock of geese on the way to the car in Helsingborg on 18th April. I had a quick look in the camera and saw that the geese were Barnacle geese. When I downloaded the pictures to the camera that evening I saw that the formation of geese was being led by Curlews. I've never seen or heard of this behaviour before. Is is common and why would 2 very different species cooperate in this way? I've heard of mixed flocks of geese but this is something else.

The laws of fluid dynamics don't care what species you are. A man on a bicycle can ride faster behind another cyclist, and even faster behind a truck.

A slightly closer analogy would be dolphins surfing the bow wave of a ship. A bigger ship makes a bigger wave, but any ship will be much better than swimming alone.

For this kind of drafting (the kind that makes the classic V shape flock), it makes a difference what size the other birds are (or rather, their wingbeat frequency), but for birds that are close in size, strict sorting would cost more effort than it saves. Still, it's interesting that the curlews are grouped in front - this perhaps suggests that the geese came along and followed the curlews opportunistically.


As long as the two species don't perceive each other as threats, they should cooperate just fine. It would be interesting to see whether they rotate the lead in a fair manner, as geese usually do, or whether the geese continue to let the curlews lead.

Notice the much smaller Curlew, could this be a Whimbrel? Assuming they're all more or less at the same height for the aero dynamics ( slipstream / efficiency).

Thank you very much, natreb! That makes a lot of sense and I did wonder if the geese were opportunists taking advantage of the curlews.

I'll have another look at the smaller curlew, Pyrtle! A whimbrel is definitely possible in that place at that time.

nartreb said:

A slightly closer analogy would be dolphins surfing the bow wave of a ship. A bigger ship makes a bigger wave, but any ship will be much better than swimming alone.

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Interesting that dolphins do this - that the advantages of the hydrodynamics outweigh the discomfort of being deafened by the engines, and the life-threatening risk of propeller cut wounds.

Macswede said:

I'll have another look at the smaller curlew, Pyrtle! A whimbrel is definitely possible in that place at that time.

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Bill length looks the same to me; I think the apparent smaller size is just an effect of the wings being at a different point in the flapping cycle.