Nature: Crossbills an ever-evolving species

Red crossbills (female above, male below) have primarily stayed north of Ohio this year

Columbus Dispatch

February 18, 2018

NATURE
Jim McCormac

For birders, one of the most exciting avian winter events is an irruption of winter finches. Not eruption, as in a blowing volcano. Irruption refers to a mass migration of birds to a new region, usually because of food shortages.

Winter finch irruptives include northern species such as common redpoll, evening grosbeak, pine siskin and purple finch. Perhaps most exciting, though, are the crossbills.

There are two eastern species, the red crossbill and white-winged crossbill. This winter showed promise for the former, and there have been a number of Ohio sightings. However, the majority of red crossbills stayed north of Ohio.

Crossbills are boreal breeders, nesting in the great swath of coniferous forest that stretches across Canada and the northern U.S. Their range also extends along mountain ranges in the east and west, where pine or spruce forests occur.

These scissor-billed finches are uniquely adapted to harvest seeds from conifer cones. A crossbill’s mandible tips are elongated and curve strongly in opposite directions, as if the bird suffers a deformity. The bill’s odd shape is a perfect adaptation for popping open tight cone scales so that the bird can access the seed within.

A crossbill in a feeding frenzy can harvest seed at a remarkable rate. It will deftly grasp the cone with its feet, parrotlike, while forcing the cone scales apart. A long barbed tongue flicks the seed out in the blink of an eye. An ambitious bird might harvest 2,000 of the nutrient-rich seeds daily.

I’ve made two trips to Algonquin Provincial Park in Ontario, Canada, this winter. The abundant white spruce in that region are experiencing a boom year for cone production, and crossbills are everywhere. Even though it’s midwinter, the crossbills are showing signs of nesting. Breeding can occur at almost any time of year if food sources are plentiful. The tough finches are unaffected by brutal cold. Winter temperatures in Algonquin regularly plunge far below zero.

Crossbills are highly nomadic, a lifestyle forced by the irregular production of cone crops. Most conifers — spruce, pine, hemlock, etc. — produce bumper crops of cones only every other year, or at even longer intervals. Thus, what might be excellent habitat one year could be nearly lacking in food the next.

On a geological time scale, boreal forest habitats in their current distribution are modern. The last glacial advance retreated from Ohio only about 10,000 years ago. Up until a few thousand years ago, spruce, fir, pine and other conifers covered much of the state. Now one must travel a few hundred miles north to find this habitat commonly.

Red crossbills seem to be in a state of active evolution, still changing with the shifting coniferous forests following glaciation. Ten “types” have been delineated, and one of these, the western Cassia crossbill, was described as a distinct species last year.

The various crossbill types differ in bill shape and size, and are adapted for feeding on different cone sizes and shapes. Our ability to tell them apart is evolving, and identification rests largely on differences in call notes.

In a way, the red crossbills are the Darwin finches of the north, actively evolving to exploit shifting niches. Someday, ornithologists might split the red crossbill complex into 10 species.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

Red Crossbills for the plucking

Photo: Chuck Slusarczyk

Red as a brick and plump as a sheep, a splendid male Red Crossbill, Loxia curvirostra, sits among the spiny orbs of Sweetgum fruit.

Chuck Slusarczyk of Cleveland sent along news and photos of Red Crossbills from Cleveland's West Park Cemetery. Chuck and Liz McQuaid discovered about a half-dozen of the x-beaks here on December 30th, 2012, and the boreal finches have been delighting scores of visitors ever since. A smattering of White-winged Crossbills, Loxia leucoptera, and Common Redpolls, Acanthis flammea, have also been seen.

Photo: Chuck Slusarczyk

A bit more somber than her male counterparts but no less interesting, a female Red Crossbill digs into the Sweetgum, Liquidambar styraciflua (lik-wid-am-bar sty-ras-ih-flu-ah. Whoa! Nine syllables on that one!). Crossbills, siskins and other finches seem to really go for the fruit of this tree. I find this choice of food interesting, and wonder if irruptive finches from the Great White North have always noshed on Sweetgum. The native range of this tree barely extends to the latitude of southern Ohio; everything north of there is the result of ornamental plantings. Regardless of whether these birds have always known of Sweetgum's charms, or if it is a recent culinary discovery makes no difference to the finch-seeking birder - just check those bristly balls of fruit for birds!

Chuck kindly included a link to a map to West Park Cemetery: https://plus.google.com/109379624892144334838/about?gl=us&hl=en

If it's crossbills you seek, give West Park a go. Congrats to Chuck and Liz for finding these birds, and special thanks to Chuck for generously sharing his photos with us.

Red Crossbills!

The Cranberry Mountain Nature Center, high in the Monongahela National Forest. A fabulous place, in a magical setting. Note the large red spruce, Picea rubens, growing to the left of the building, as they are important to this story.

Last Thursday, I was co-leading an expedition to nearby Cranberry Glades Botanical Area as part of the New River Birding & Nature Festival. We were strolling the road, when I heard the sharp kip-kip-kips of a Red Crossbill, Loxia curvirostra, flying over. These odd boreal finches are probably the most coveted of the bird species that might be encountered on this trip, and most years we fail to find them. While nearly all of the group heard the bird, and some saw the distant speck as it hurtled overhead, this was not a very satisfying immersion into the world of crossbills, and this would be a life bird for most in our party.

Around noon, we repaired to the aforementioned nature center to eat, and as it was a nice day we sat outside at picnic tables. As usual, I had one ear cocked outward, listening for whatever might happen by. Before long, I thought I heard the distant chatter of a crossbill, and quietly stepped away for a quick scan. And there it was - teed up on a spruce across the road! I let loose with a quiet shout, the group sprang to life, and we had it in the scopes in a wink. Everyone got the bird before a noisy logging truck steamed past, spooking the x-bill, which was not to be seen again that day.

I then went into the center to query the staff about these birds, knowing from past visits that they were familiar with the species. "Oh yes, they've been around all winter and we've got up to 30 coming in each morning" came the report! Turns out the nature center staff discovered by accident that crossbills enjoy snacking on salt, and they were casting the stuff right outside the garage doors.

Well. With this intelligence in the bag, we modified the next day's visit to Cranberry Glades and went straight to the nature center, leaving the glades for later. Sure enough, no sooner than we exited the bus, the distinctive notes of crossbills greeted us. Our gang of 20 stealthily sneaked up and set up shop about 50 feet from the salting station, and were rewarded with stunning views of these handsome birds.

Nature Center staff reported that the crossbills wouldn't even fly when they opened the outside door and stood four feet away. Turns out the birds had learned to recognize them, and were comfortable with their presence. They said that I could snap some photos from the doorway, and after everyone had been satiated with good looks, I gave it a whirl. The birds DID NOT recognize your narrator, and flushed. But they were soon back.

When we returned to the center for lunch, the crossbills were still hanging out, and once again I tried shooting from the door. This time, the birds did ignore me, and I was able to take the photos in this post with my point and shoot from less than five feet, at times. The pair above is a male and a female, the former being the one with the brick-red plumage. Note their large parrotlike bills with the distinctive crossed mandibles. We were quite excited to see at least one fresh juvenile with the flock; a bird that probably has only been out of the nest a few weeks and was still heavily streaked.

Crossbills use their strange tong-bills to force open the scales of conifer cones. The bird then darts its barbed tongue into the cone's depths and deftly extracts the protein-rich seeds. They're good at this, and an adept bird is said to be able to harvest several thousand seeds per day.

Red spruce dot the summit of nearby Black Mountain, which rises to over 4,500 feet. We had a dozen or so flyover crossbills here as well. The spruce are their primary food source, and as spruce cone crops go, so goes the crossbill. When cones are abundant, the crossbills respond and rear more young, and in lean crop cycles the birds can be scarce and quite tough to find.

Stately and symmetrical, this towering red spruce was crowned with dense masses of cones, ripe for the plucking. So were just about all of the mature trees that we saw, and thus the crossbills are like feathered kids in a coniferous candy shop.

Map courtesy of BirdFellow

This excellent map, produced by avian distribution expert Paul Lehman, depicts the overall distribution of Red Crossbill. The purple areas denote the breeding range.

But there is more to the story.

Red Crossbills are a complex species, and have been divided into nine "types". Some authorities believe that all of them warrant recognition as distinct species; others think that at least a few of the types should be split out; and conservatives such as your blogger feel that the types perhaps merit subspecies level distinction at best.

But it is possible that some carving up of the Red Crossbill may occur in the future. If so, we'll have to work hard to determine which types these southern Appalachian crossbills are. Apparently they are most likely the so-called Type 1 or Type 2 populations. The best - only? - way to separate the types in the field is by vocalizations, so if any "new" species are split, you can be assured there will be many birders trying to master the subtleties of Red Crossbill calls.