In the fall, I had high hopes for a winter with tons of northern finches.  Red spruce, balsam fir, tamarack and eastern hemlock trees were producing bumper crops of cones.  These so-called mast years occur sporadically and different tree species do not necessarily have mast years in the same years.  This winter was shaping up as a marvelous smorgasbord for the finches that depend on conifer cones for their main food.

As a baseball fan, I can’t help but think of the movie Field of Dreams where Kevin Costner’s character builds a ballfield in his Iowa cornfield because a voice told him ”If you build it, he will come”.  Sure enough, the ghost of Shoeless Joe Jackson and other members of the Chicago Black Sox show up to play baseball.

But with our finches, the presence of a bumper crop of food is not enough to guarantee their presence.  If trees build large number of cones, the northern finches may or may not come. Obviously, these nomadic birds are finding sufficient food elsewhere.  The absence of all of these seed predators is good news for the trees of course because many seeds will find their way to the ground and germinate.

Pine Siskins, Common Redpolls, Pine Grosbeaks, Purple Finches, Evening Grosbeaks, White-winged Crossbills and Red Crossbills were all pretty scarce on Maine Christmas Bird Counts.  On a recent trip to the Cobscook Bay area, I found very few northern finches despite the many conifers heavily laden with cones.  However, a recent trip to the Flagstaff Lake region yielded sightings of good numbers of both crossbill species.  Perhaps we will see a late-winter irruption of some of these species into more southerly parts of our state.

Of the northern finches, the crossbills are perhaps the most erratic in their appearances in Maine.  Watching crossbills feed is to marvel at their skill in extracting conifer seeds with their peculiar bills.  The hallmark of the crossbills is the odd overlapping arrangement of the upper and lower bill. When observing a crossbill from above or below, one can see that one bill curves left and the other curves right. Sometimes, the upper bill is the left-curving one and in other birds the lower bill curves leftward. Why such a strange bill?

This bill turns out to be an efficient took for extracting conifer seeds.  Everyone knows what the cone of a pine, fir, spruce or other conifer looks like. The cone has a number of scales. At the base of each scale, the seeds of the conifer can be found. Most birds have a difficult time negotiating the scales to get to the seeds deep within the cone.

Not crossbills however. A crossbill inserts its bill between two scales of a cone. The crossed points of the bill act as a wedge, increasing the distance between the two scales.  One bill pushes to the left and the other to the right. The strong tongue of the crossbill can then be inserted to the base of the scale and the nutritious seed removed and gobbled up.

Although the crossed bill serves these birds marvelously in feeding on cones, the specialization comes at a cost. Crossbills are quite awkward in handling food that other finches readily eat such as thistle or birch seeds. A crossbill beak is not a generalized tool.

Usually crossbills feed on cones that their bills can handle with greatest efficiency. The Red Crossbill has a larger and longer bill than the White-winged Crossbill. Red Crossbills feed on white pine, balsam fir and sometimes hemlock cones. White-winged Crossbills feed on smaller cones like those of larch and red spruce.

Here’s hoping the crossbills will come further south this March so we can all admire the skill with which they extract conifer seeds.

[Originally published on March 18, 2012]