Yellow-bellied Sapsucker Phloem Wells in Birch

These sapsucker wells were 5-6 mm in diameter. These are phloem holes, which are made in horizontal and vertical rows.

Trees make two kinds of sap. The sap that's readily tapped in early spring for maple syrup is xylem sap, which is a thin liquid that carries water and little nutrients from the roots upwards to the leaves. Phloem sap carries the nutrients produced in the leaves downward to other parts of the tree.

Sapsuckers usually choose trees that are wounded or weakened because the sap of trees that are in poor health contains higher levels of amino acids and protein. These holes were made in a birch tree (probably last summer), which had since fallen.