The case of the Missing buds: Deja vu
Periodically, a pine plantation comes through winter with extensive damage to the terminal shoots and topmost branches. The terminal shoots are devoid of buds and some of the lateral branches are broken. This damage is occasionally seen in northern Minnesota on Scots, white and red pines and white spruce. Trees seven to ten foot in height seem to be the targeted size class. By mid-summer, the upper most crowns have a "brushy" appearance. Ultimately, this damage results in stunted growth and, sometimes, deformed trees. Not good if you are a Christmas tree grower.
Pine grosbeaks are known to cause this kind of damage when feeding, as they perch on the laterals and dine on the terminal buds. It is important to point out that trees are not killed by this activity. Pine grosbeaks are robin-sized birds. Males are rosey-pink in color and have a stubby, stout bill. The females are gray, with a dull yellow crown and rump. Their natural habitat is the cold spruce forests of Canada where they live and breed. Every four to five years, they migrate southward during winter months in search of food. In the Boreal Forest Biome, they normally feed on buds of spruce and fir trees which have characteristically shorter, stouter branches that can support their weight. The slender and delicate branches of pines are more easily damaged, especially when frozen.
If you want definitive proof that pine grosbeaks are the culprits, you might try sitting out in your red pine plantation January through March to catch them in the act. Bring binoculars. A better alternative is to check with your friends that maintain a bird feeding station. This is definitely a warmer way to correlate plantation damage to the grosbeak population cycle. Our friends reported pine grosbeaks at their bird feeders during the past winter.
Pine grosbeaks are protected by the Federal Migratory Bird Treaty Act, so don't remove or bother the grosbeaks. However, the landowner may do the following type of control:
- If practical, install an audio devise to discourage "looting" of the buds.
- Shear damaged trees to obtain uniformity of form and shape.
- Place a plastic mesh, or sleeve over the topmost shoots after the trees become dormant in early winter or late fall. Be sure to remove them the following spring.