The case of the missing white spruce buds

In a plantation near Orr (St. Louis County), white spruce appear to have been browsed. Terminal buds and some lateral buds were cleanly nipped off. The budless branch stubs look like deer nipped them off. The only problem is that the trees are 10 to 15 feet tall. Since the first sightings, similar damage has been found in a plantation in Itasca County as well.

white spruce buds eaten by grosbeaks

Was this caused by deer on stilts, or perhaps a few migrating giraffes that lost their way?

According to the Christmas Tree Pest Manual, the most likely culprits appear to be pine grosbeaks. In winter, pine grosbeaks are known to feed on buds in the upper crowns of pines and spruce. Every four or five years, large numbers of pine grosbeaks move into Minnesota, apparently leaving Canada in search of better weather or more food.

Any other ideas?