Shorebirds using their feet

To: birding-aus <>
Subject: Shorebirds using their feet
From: Vader Willem Jan Marinus <>
Date: Thu, 16 May 2013 07:49:21 +0000

This is a topic that has long interested me, and I think I may have written 
about it to Birding-aus years ago (My home computer has crashed, and I have no 
access to my archives just now). Just the other day I watched a Northern 
Lapwing foot-shivering on very wet grassland: it stretches out one foot and 
very rapidly shivers it. as far as I can see, the foot barely touches the 
ground, making the often heard suggestion that this drives worms out of the 
ground not a very convincing one, to my eyes. I think that it is more probable 
that the movement frightens small prey animals, so that they move and are 
easier seen by the lapwing, as all plovers an eye-hunter. I do not know if this 
foot-shivering occurs in many Vanellus lapwing species; we don't have more than 
one here in N. Norway.  Similar foot movements with one foot at the time, 
although the shivering is at a much lower frequency, can be seen in different 
species of egrets, and I should think the aims are the same, i.e. getting prey 
animals to move and become more conspicuous.

Foot-trampling by gulls, which is of common occurrence in many of the smaller 
gull species, is quite different. Here the gulls trample with both feet , 
either at one spot, or slowly moving backwards; I have years ago (1975?) 
published pictures of the tracks this leaves on mudflats in a Norwegian journal 
 The Common Gull Larus canus (I am too old to be able to learn the recent 
splitting of Larus into a number of smaller genera) is an inveterate trampler 
on mudflats, and I've watched the behavior in a number of other species all 
around the world: Ring-billed and Bonaparte's Gulls on the US east coast,  
Hartlaub's Gulls in S. Africa and also Silver Gulls in Australia. In all these 
cases the aim of the behavior is IMO the liquefaction of the substrate mud, 
which makes small prey animals 'float up'. One can easily imitate this process 
by 'hand-trampling' at the same places.

Also our Black-headed Gulls L. ridibundus trample quite a lot, and they are the 
species where the behaviour was first observed. But they also trample on 
grassland (Wonderfully watched recently on quite dry grassland in a small park 
in Odijk, Netherlands), and it was there that the behaviour was first observed, 
i.a. by the great Nico Tinbergen. Also here the 'driving out of worms from the 
ground' is one of the theories for explaining this behavior, and in this case 
liquefaction of the substrate of course can not be the right explanation. As 
far as I can see, the foot-trampling of the gulls on mudflats and on grassland 
seems to be exactly the same behavior pattern, so the question is : what came 
first? As gulls originally are shore birds, I think maybe the mudflat trampling 
is the original one, but I may be wrong.

Nobody has, as yet, mapped in which gull species this foot trampling occurs; I 
have not seen it in the large white-headed gull species, but it seems 
widespread in the smaller species.

                                                        Wim Vader, Tromsø Museum
                                                             9037 Tromsø, Norway

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