Monday, February 20, 2012

White-winged Crossbills

A young White-winged Crossbill, Loxia leucoptera, poses at arm's length in an Eastern hemlock that is festooned with cones. The bird still shows the heavy blurry streaking of a juvenile.

I was up in the Toledo area last Saturday, to meet with photographer Brian Zwiebel about a project that we are collaborating on. Brian lives but 25 minutes from Woodlawn Cemetery on Central Avenue in Toledo. Woodlawn is legendary for attracting winter finches, and this year there has been a pack of up to 100 White-winged Crossbills present. We really wanted to observe and photograph the x-bills, so after our work was done, off we went.

Woodlawn's 160 acres is heavily populated with magnificent trees, including many stately cone-bearing conifers and fruit-laden alders and sweetgum. Thus, its attraction for seed-eating winter finches. By the way, this photo was taken with my Droid smart phone. The cameras in these latest generation phones are becoming insanely good, especially for landscape scenes.

We had barely stepped from the car when a couple of friendly birders wheeled up and reported the crossbills in a nearby sweetgum. A short few minute walk and we were there, and so were the crossbills. About 15 birds were plundering the spiny balls that copiously adorned a large sweetgum, which has one of the most mellifluous of botanical names: Liquidambar styraciflua.

I don't really think of sweetgum as the fruit of choice for crossbills, but there they were, digging in with gusto. A pink adult male is bottom center, and look closely and you'll see three females, or parts thereof. Two other of the spectacular adult males were present, and one young male who was beginning to develop a pinkish bloom on his breast. The remainder of the flock were adult females and juveniles.

It wasn't long before the flock erupted into flight, filling the air with harsh electric jips. Crossbills are real talkers when not busy stuffing their faces, especially when aloft. We had no problem tracking them to this large Eastern hemlock, Tsuga canadensis. White-winged Crossbills depend heavily upon the cones of spruce, especially white spruce, Picea glauca, when in the boreal forest. When they irrupt to more southerly latitudes, south of the range of spruce, they really go for hemlocks and their small cones. Fortunately, cemeteries are fond of planting hemlock which is one of the reasons that graveyards make good places to seek winter finches.

A female White-winged Crossbill makes mincemeat of a hemlock cone. Note how she grips it with her powerful foot, and then inserts her oddly shaped asymetrical mandibles between the cone's scales. Using the crossed upper and lower mandibles like tongs, the crossbill quickly forces open the protective scales, allowing access to the tasty seed within.

The crossbill doesn't pluck the seed with its bill - it uses its long barbed tongue for seed extrication. In this photo, the tip of the tongue can just be seen, caught in the act as the bird flicked it into the cone's interior. White-winged crossbills are incredibly adept at accessing conifer seeds, and work through cones with astonishing speed. I took hundreds of photos on this foray, and only a few images show the tongue in action.

Although the clarity of this photo would have benefited from a faster shutter speed, you can clearly see the crossbill's long pink tongue plumbing the depths of the cone's scales. This whole process - forcing the scales apart, and tongue-flicking the seed out - happens so fast that the bird's actual technique is not really visible, apart from the scale spreading.

Once crossbills are immersed in seed-eating, the flock usually falls silent and it would be quite easy to pass by a tree full of feeding birds. One give-away is the soft cracking and crunching of cone scales being fractured, and the gentle rain of cone fragments drifting to the ground.

Here's what the crossbills lust for - conifer seeds. These are the scales of a hemlock cone, and a shiny oblong-shaped seed remains at the base of the scale on the right. Conifers are part of a plant group known as Gymnosperms, which translated literally means "naked seed". Naked these fruit may be, but that doesn't mean that the conifer doesn't do a good job of protecting them within the tight woody scales of cones.

I've extracted a few hemlock seeds - much more clumsily than a crossbill, I might add - so you can see how small they are. What conifer seeds lack in size, they more than compensate for in nutritional value. They are the cashews of the boreal forest, loaded with rich fatty oils, and it makes complete sense that a group of animals would have evolved the ability to efficiently harvest conifer seeds.

And boy, can crossbills harvest seed. It is claimed that a hard-working White-winged Crossbill can pluck 3,000 seeds a day! CLICK HERE for an incredible video of crossbills feeding.

Distribution of White-winged Crossbills in North America, courtesy the Cornell Lab of Ornithology. Their range mirrors that of the vast belt of conifer-dominated boreal forest that sweeps across the northern part of the continent.

Crossbills play an integral role in the ecology of the boreal forest. Their North American population is estimated to be about 20 million birds. While a single bird is claimed to be able to harvest 3,000 seeds a day, let's be more conservative and knock that back to 1,000 seeds daily. If I did my math correctly, that equates to the entire North American White-winged Crossbill population consuming something on the order of 20 BILLION seeds daily! That's hard to fathom, and even if one were to quibble about the numbers, the fact remains that crossbills consume an enormous number of conifer seeds.

Not all of those bony little fruit get digested. Some of them are sure to pass through the crossbill intact, and possibly even scarified and ready for germination after exposure to digestive compounds. Thus, the crossbills serve as a giant army of feathered Johnny Appleseeds, spreading fir, hemlock, spruce and other conifers about the Great White North. When one considers the youthfulness of the boreal forest - this region was under a mile of ice only ten thousand +- years ago - it stands to reason that crossbills played an enormous role in reforestation of the boreal following the withdrawal of the ice sheets.

Crossbills are a blast to watch. Brian and I spent several hours watching the Woodlawn flock, and ended up overstaying our welcome. We arrived at the gates to find they had already been locked, and we had to phone the very nice security officer to release us.

As few if any people inhabitat much of the remote boreal forests where crossbills breed, the birds do not seem to acknowledge humans as a threat. It is easy to quietly sidle up to within a few feet of a feeding bird. As long as you don't do anything suddenly or loudly, the crossbill will utterly ignore you and continue about its business. To me, they suggest little parrots. Just like many of the Psittacids, crossbills use their feet to hold food, and of course their crossed bills are like Swiss army knives and vital to the extraction of food, just as with parrots. Another endearing parrotlike habit of crossbills is their tendency to pull themselves about with their bill.

A White-winged Crossbill makes for a heck of a "spark bird", and perhaps that's the case here. A number of other birders were in the cemetery admiring the crossbills, including this young man, Nathan. He is pointing at a crossbill that is only about three feet from his outstretched finger, and it looks like the bird made an impression.

These White-winged Crossbills have been present in Woodlawn Cemetery for a month or so, and may persist for a few more weeks. The cone crop is quite luxuriant in the cemetery so there is still plenty of food. Also, it appeared as if much of the remaining untouched cones are near the ground - low-hanging fruit, if you will - and that means your chances of seeing the birds up close and personal is good.

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2 comments:

OpposableChums said...

I see by the pictures of your palm that you will meet a tall dark stranger and live a very long life.

nina said...

Fantastic crossbills, Jim! Bravo!