Foot-use while foraging by the Australian passerine, Grallina cyanoleuca

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I have just observed a behaviour, on the part of a bird in my suburban garden, that may perhaps not have been noticed previously.

The species concerned is Grallina cyanoleuca (https://www.inaturalist.org/taxa/8583-Grallina-cyanoleuca).

This species is fully indigenous and wild. However, it is so extremely habituated - without particular encouragement - that it frequently approaches me to within one metre, while I am active in my garden.

This morning, I happened to throw a small slice of cheese, about 2.5 cm long and wide, and 2 mm thick, to a single individual of G. cyanoleuca, that happened to be foraging close to me on a uniformly paved surface (similar to https://www.dreamstime.com/stock-photo-australian-magpie-lark-peewee-bird-eating-food-scraps-black-white-grallina-cyanoleuca-also-known-as-mudlark-tiled-floor-image41093873).

The bird pecked at the cheese repeatedly, trying to detach fragments small enough (crumb-size, less than 5 mm long and wide) to swallow. Although I am familiar with this reaction, I noticed for the first time that the bird intermittently used one foot to assist.

Various spp. of birds, worldwide, are well-known to use a foot to hold down food as they process it with the beak.

However, what G. cyanoleuca did, on this occasion, was different. Rather than placing the foot flat on the cheese, it clenched the toes somewhat, as if to try to grasp the item.

This attempted grasping was done so ineptly that I did not see any instance in which the cheese was actually held firmly for pecking. This was probably because the cheese was too thin to be easily lifted. However, the inadvertent effect was perhaps to help to stabilise the cheese, by the application of the weight of the somewhat clenched foot.

Overall, my impression was that the use of the foot on this occasion was ineffective, owing to achieving neither a full weighting nor a full grasping. However, what I found noteworthy is the attempt in the first place.

Please bear in mind that, in fully natural circumstances, G. cyanoleuca would be unlikely to find a food item of such flatness and rubbery texture, lying flat on a hard, smooth surface.

Anyway, my curiosity aroused by the observation, I consulted the Web, on the topic of foot-use by this species. I found the following photo.

Please scroll in https://nzbirdsonline.org.nz/species/magpie-lark, for a photo - lacking any explanatory caption - by Peter Reese, of an individual of G. cyanoleuca, successfully grasping a food item in one foot.

I also found that it is well-known that G. cyanoleuca uses its feet in a different way, to expose food items such as earthworms: https://www.birdlife.org.au/afo/index.php/afo/article/viewFile/1040/1013 and https://besgroup.org/2014/07/14/magpie-lark-foraging-for-food/.

This is my commentary.

In general, various animals differ greatly in dexterity. Among birds, there seems to be an approximate correlation between dexterity and braininess.

Grallina cyanoleuca is not brainy for a bird (see data compiled by Iwaniuk). It would therefore not be expected to show dexterity.

For these reasons, it comes as something of a surprise that G. cyanoleuca not only uses its feet to assist in foraging, but grasps food items as opposed to merely holding them down.

This can perhaps best be illustrated by comparison with Corvus coronoides (https://www.inaturalist.org/taxa/8040-Corvus-coronoides). This species is likewise fully indigenous and wild, and also frequently forages in my garden - albeit always eyeing me warily, and keeping a distance of at least two metres.

(Please see https://pubmed.ncbi.nlm.nih.gov/15896533/.)

Corvus coronoides certainly places a foot on food while pecking at it, in order to hold it down (https://depositphotos.com/49228971/stock-photo-australian-raven-eating-from-a.html). However, I have never seen it trying to grasp any item in its toes.

Corvus coronoides is far brainier than G. cyanoleuca. Therefore, is it not somewhat surprising that it is the latter that shows some ability to grasp food items?

Publicado el agosto 21, 2022 01:48 MAÑANA por milewski