March 30, 2014

True Grit

American Goldfinches

There was another bird-related occurrence from that last weekend I visited my folks. And now that my excitement over those Purple Finches has subsided a little (don't take that to mean it has completely subsided, strangely enough, it hasn't), I'm finally ready to look into it.

I saw the above sight early on that Sunday morning: a flock of American Goldfinches clinging to the brick wall of the house - not exactly the most typical perch for a Goldfinch. What were they doing? The weather wasn't bad (other than being really cold), so shelter didn't really make sense as an explanation. When I googled this phenomenon, I read some claims that they might do this because they're eating bugs off the wall (not too likely in Ontario in February), but the last response in that thread agreed with Dad's assessment and the old man, as a former colleague of mine used to say, knows a thing or two about a thing or two.

American Goldfinches
For the same reason that you'll often see small flocks of birds on the gravel shoulders of country roads, these Goldfinches were pecking at the mortar to get some grit. With snow and ice covering every inch of the ground, including the gravel driveway, this was the closest source of grit for the finches. Birds have a two-stage stomach, the true stomach (proventriculus), which secretes the digestive enzymes, and the gizzard (ventriculus), where they keep grit and small stones which help grind up tougher-to-digest foods like seeds. Since birds don't have molars (or any teeth, for that matter) they need grit to do this job so they can get the most out of the food they eat in these cold winter months.

Another possible explanation is there is limestone in the mortar and they could be ingesting it for the calcium carbonate. This is a key nutrient in the formation of eggshells and since they'll be nesting in a few short months, so it could be that this is the reason for this strange behaviour. I don't know if it really has to be an either/or situation...I'd rather think of it as a two birds with one stone kind of thing.

[Update: I've just come across this post from a UK blog - The Rattling Crow who observed the same thing with European Goldfinches...and summed it all up much more concisely than I did—Ed.]

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