THE SHRIKE'S LARDER [Ref]
Our northern shrike is a songbird which has developed feeding habits along the lines of those of a hawk. Whereas most birds its size are content with fruits, seeds, or insects of a size it can beat or bite and then swallow whole, our northern shrike takes not only small insects but prefers large ones, and mice and birds too big to be swallowed whole. It is an opportunist and takes what is most abundant and easily accessible. The shrike's strong hooked bill is a powerful weapon, used with a nipping motion that is directed at the back of the head or neck of mouse or bird.
Now with the dead sparrow or mouse the shrike is at a disadvantage. With a powerful bill hooked at the tip its feet are still those of a songbird and are not strong enough to hold its large prey while pulling it to pieces. Only small insects are held in one foot and pulled to pieces. To meet this need for holding large dead prey the impaling habit was evolved. The result of this is the so-called larders, which form a fancied resemblance to meat hanging in a butcher shop, and have given the birds their name of butcherbird. A thorn tree, a splintered end of a branch, or even the barbs of wire fencing may serve. The shrike flies to one of these, carrying the prey in its bill (rarely in its feet), and with a pulling motion fixes the prey on a projection point. Sometimes instead of impaling the mouse or bird it pulls it into the fork of a branch, and so wedges it there. Now the food is firmly held, and the shrike can use its bill effectively to pull off pieces of flesh and swallow them. When the bird has fed, it leaves the rest of the animal hanging where it was. It may return to this food and make repeated meals of it if not spoiled, or dried up, until the whole is devoured. But often parts of meals are left hanging and discarded. If suitable thorn bushes are scarce the shrike may return time after time to the same tree with its prey, and in time this tree may come to be decked with many partly devoured carcasses. Such trees are the so-called "larders." There is another aspect of shrike behavior that adds to these larders. The shrike, even when replete, may seize any prey that appears and impale it. The bird's organization is such that the sight of a small moving animal may start the actions that end with impalement even when the bird is not hungry. This food usually is not eaten later.
Thus the shrike's "butcher shop" is not primarily a store of food, even though it sometimes serves as such when in times of scarcity remains of old meals are eaten. It is not a gathering of food in time of plenty and saving it for a later use. Rather the placing of many items in one tree is the result of its being a favorable impaling place. And the impaling is behavior developed to overcome the weakness of the claws in a bird whose disposition and strong beak enable it to prey habitually on larger animals which otherwise it could not tear to pieces and eat.