Grackle’s Ravenous Mind - technique of cracking open bivalve mollusc shells

To save space I will only point out a few known facts. In short:

So far I only found very little in published literature about ‘blackbirds’ feeding on bivalve molluscs. Crow Blackbird [Common Grackle (Quiscalus quiscula)] was listed as a bivalve predator but no description of process was included (1900).

Many shorebirds feed on bivalve molluscs in intertidal zone but they usually swallow the whole prey (so one of rules of ingestion is set by the gape width) and later undigested shells can be found in droppings or regurgitates. I also documented other birds feeding on bivalves and regurgitate shell remains.

Some birds will ingest and digest shell fragments to balance calcium deficiency, especially during egg laying periods.

The Norse supreme god Odin was often shown with his two ravens: Hugin ("thought") and Munin ("mind").
And all Corvids were always symbols of intelligence in the animal word. Recent scientific research shows that many corvids rank very high among most intelligent animals; there is evidence that the clever birds may very well surpass the great apes in intellect. Perhaps corvids might be the most intelligent birds but many other individuals from different avian families are quite clever as well.

Here I want to show not only Great-tailed Grackle preying on bivalve molluscs found in intertidal zone but also describe a technique of cracking open bivalve shells allowing grackles to ingest only the soft body of the mollusc. Meal is served on half-shell.

First I will present the most interesting part - technique of cracking one of the two half-shells of the bivalve mollusc so meal can be served. It might takes the grackle a several tries but when he finally grasp firmly the edges of one half-shell between under and upper tomium and anchor tip of the bill in the ground he is ready to crack the shell. Now he only needs to squeeze the shell to crack one half and have an easy access to the mollusc body. Red arrows are pointing to the contact zone between one of the bivalve half-shell edges and grackle’s tomia.

A lot of time and effort to get so tiny meal but as we all know there are a lot of people spending time cracking open sunflower seeds.

Here are a few selected photos showing the whole process from finding a bivalve, cracking its shell and getting the meal. As you will see in one photo every time bivalve shell is not placed correctly between tomia, bivalve will be expelled to the side of the bill when pressure is applied and bivalve will stay safe, temporarily, inside uncracked shell.

BTW the presence of scopate tomia was documented in roughly 30 avian families. There is some circumstantial evidence that “hardshelled” dietary items, such as snails and large insects, provide a common
denominator linking scopate tomia to feeding habits. In many icterid genera, for example, the tomia are certainly modified in that a narrow, somewhat irregular, differentiated ridge is present along the cutting edge, but these “pseudoscopate” brushes have a vitreous appearance suggesting a brush clotted with hardened varnish.

Ref.
GOSNER, K. L. 1993. Scopate tomia: An adaptation for handling hard-shelled prey? Wilson Bull. 105: 316-324

Perhaps not the most interesting GTGR behavior I ever observed and photographed but I found myself being fascinated watching grackle’s precision in manipulating these small objects.