Feeding association between Coots and Gadwalls (1 Viewer)

A week or 2 ago John Butler reported having seen a Red-knobbed Coot who was diving for food but that was eaten by a Gadwall.

I then replied that I had read of simmilar occurences that were reported in British Birds. Unfortunately John's thread then was lost during the Great Birdforum Disaster.

Later I had a look at copies of articles about Coots I had made.

Several studies in the USA showed that it was a common practice. The study also showed that this stealing of food was mostly done by subordinate Gadwalls (females or unpaired ones).

As Coots and Gadwalls eat the same food this stealing allowed the Gadwalls access to food they normally would not have been able to get (Gadwalls can't dive that deep).

It also showed that Coots that were attended by Gadwalls dived more that unattended Coots (sometimes 4 Gadwall to 1 Coot).

The lack of agression was explaned thus: the food that was brought to the surface was not very nutritional so there was no need to defend it.

In one study there was also mention that (in other studies) Coots also benefited from it but I haven't read or seen those yet.

Ronald Zee said:

The lack of agression was explaned thus: the food that was brought to the surface was not very nutritional so there was no need to defend it

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Probably a silly question, but why do the coots therefore dive for it in the first place ??

AnnieW said:

Probably a silly question, but why do the coots therefore dive for it in the first place ??

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That was my thought as well, maybe lack of other food resources.

"That was my thought as well, maybe lack of other food resources."

It has been suggested that a buoyancy problem accompanied with the design of the feet create a lack of downward drive and the associated sustainability to hold position under water to grab, pull and detach the aquatic plant foodstuff from their root system.

Regards

Malky.

Ronald Zee said:

A week or 2 ago John Butler reported having seen a Red-knobbed Coot who was diving for food but that was eaten by a Gadwall.

I then replied that I had read of simmilar occurences that were reported in British Birds. Unfortunately John's thread then was lost during the Great Birdforum Disaster.

Later I had a look at copies of articles about Coots I had made.

Several studies in the USA showed that it was a common practice. The study also showed that this stealing of food was mostly done by subordinate Gadwalls (females or unpaired ones).

As Coots and Gadwalls eat the same food this stealing allowed the Gadwalls access to food they normally would not have been able to get (Gadwalls can't dive that deep).

It also showed that Coots that were attended by Gadwalls dived more that unattended Coots (sometimes 4 Gadwall to 1 Coot).

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Hi Ronald.

Thanks for resurecting this topic, which was lost in the server crash.

I would like to clarify a few points from your message above.

1. There were 2 Red-knobbed Coots in the area concerned, plus hundreds of Common Coots.

2. Each of the R-k Coots was attended by a single adult male Gadwall.

3. The Gadwalls were not "stealing" the weed from the coots. The coots would dive, collect weed from the bottom of the lagoon and then pass it, beak to beak, to the Gadwalls.

4. At one point a Common Coot tried to take food from one of the the R-k Coots. The Common Coot was attacked and chased some 15 metres. After the chase, the R-k Coot then paddled back to the Gadwall and continued diving and feeding it.

Although there were many Gadwalls present, no other Gadwall approached these two R-k Coots.

6. Although there were hundreds of Common Coots and many Gadwalls on the lagoon, no other coot was closely accompanied by a Gadwall and there was no exchange of food, either deliberately or by "theft", between Common Coots and Gadwalls.

As I said in my initial thread. Very strange behaviour that I had not witnessed before.

Regards from Doñana.

John.

John this shows that we do not really know much about bird behaviour.

I shall try to find the articles which mention the benefit to Coots of this feeding association.

Hi again Ronald.

Thanks for the PM. I received it two minutes after answering your comments on this thread.

With regard to your question about the "introduction programme" of Red-knobbed Coots. I think it was Jules Sykes that actually used those words.

Red-knobbed Coots are, and always have been, a feature in this region. However, people here still shoot and eat coots and take their eggs for food.
The R-k Coot is much more confiding than the common variety and you can get much closer to them. As the two species are almost indistinguishable to an untrained eye, from more than about 20 metres, this made them easy targets for hunters and they suffered badly from the "coot-shoots".

The numbers became very low about 10 years ago and were classed as a "severely endangered" species. It was decided that to try and increase the numbers, a captive breeding programme would be undertaken. This resulted in hundreds of R-k Coots being introduced into the wild over the years and is still continuing. However, the risk from hunters still remained, so all captive bred birds were fitted with a numbered white PVC neck collar. This helped to track the movements of the birds and acted as an indication to the hunters that they were an endagered species and were not to be included in the coot-shoot.

This has proved successful and the coot numbers have now increased since this method of "introduction and identification" came into being.

For some reason, Birding "snobbery" stops some birders from actually "ticking" neck- collared R-k Coots, as they class it as an introduction. This may be the case, but many of these birds have now been living and breeding in the wild for many years and should be classed as normal "tickable" birds. I certainly include them on my lists.

I do know of some people, who although they would never admit it, have digitally photographed collared coots and have then edited their photos to erase the collar. I do not think there is anything wrong with this, or even showing a photo of a collared bird.
In my mind it is a case of "they are live, they are wild, so they ARE".

Regards from Doñana.

John.

Interesting, I have heard from a birder that Coots brought food items to the surface, dropped them on the water, and they were later eaten by Gadwalls, but nothing like this...

brian holden

I have been noticing this Gadwall feeding behaviour on the Stoke Newington Res. in North London It looks like 90 or even moor % of Gadwall feed with coot most/all the time!
My take on it is that the 'thin strip weed' has insect Larva or may be small fish in it. The coot picks and shakes the weed it has dived for and then looses interest, presumably having got the protean it selectively dived for. It is then that the attendant Gadwall close in and eat the weed its self. Low nutrient, with out work, from water otherwise to deep for dabbling, as contrasted with selected protean food dived for by the coots.
The coots, when on the more restricted water of the New River are very aggressive to wards Moorhens. So if these food rivals, get attacked, why not have a 'pop' at the Gadwalls, which are about the Coots size
Why is it that the Mallards and Shoveller, also present, have not also learnt this trick; both are bigger than Coot and the latter are definitely confined to shallower areas.

brian holden said:

I have been noticing this Gadwall feeding behaviour on the Stoke Newington Res. in North London It looks like 90 or even moor % of Gadwall feed with coot most/all the time!.

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intriguing topic- in the cold snap in my neck of the woods there were Gadwall mobbing up 8:1 and full-time on an individual Coot without any fighting. I wonder whether it is simply that the Coot has worked out that it cannot fight all of them off all of the time and/or would use lot of energy doing so (whereas territorial battles etc. are more intermittent), so it is net/net more efficient in energy terms to press on and just accept the Gadwall piracy with the minimum amount of fuss.

You can also see this behaviour with wigeon stealing food from brent or Bewick's swans.