Wildlife Spotting

Some birds may drill holes in trees and then eat the sap, such as the North American yellow-bellied sapsucker does. Some trees may also exude sap to defend themselves against insect attack, essentially by drowning them or by exuding sap containing repellents. As Dan suggests it may be hard to determine what caused this tree to do what it is doing, especially without knowing the species of tree.

It's hard to tell what this is but it could be sap exuded from the tree due to a wound of some sort.