I filled my bird feeders and hung them, looking forward to the cheerful chatter of birds during winter. The next day, a chickadee or two showed up, but nothing else. A few more days went by, nothing.
One afternoon, without warning, a flock of small birds darted to and from the feeder. The suspects had bright red caps on their foreheads like berets, black around their eyes and bills, brown streaks on their sides, and some had rosy pink chests: common redpolls.
Where had they come from? Another common local bird was still missing in action — I hadn’t seen any pine siskins yet although I had seen flocks in the past. Why?
Redpolls, pine siskins, and red crossbills are all types of finches. They eat mostly seeds of conifers, alders, and grasses, although they may supplement their diet with insects or other plant bits in spring and summer. Crossbills in particular specialize in extracting seeds from the cones of spruce and other conifer trees.
These birds make home where the food is; in other words, these birds depend on seeds and sometimes travel great distances to find caches. It’s called an “irruption” when birds that don’t have a regular migration occasionally range for food. In a year when the local seed crops are poor, large numbers of pine siskins, red crossbills, and common redpolls may surge south looking for a better living, deserting their usual haunts. They can cover vast distances. In one study, a crossbill banded in Fairbanks was found near Montreal, Quebec the next winter. Common redpolls are the most predictable of the trio, “invading” roughly every two years.
Seed crops aren’t the same every year because trees have different schedules for producing seeds. Alders, a quick growing species, produce a crop of seeds nearly every year. Conifers tend to have longer cycles. Sitka spruce take about two years to produce a crop of seeds. The first year, the cones start developing, then go dormant over winter. The following spring the seeds in the cones are pollinated and ripen. Mountain hemlock produces a heavy cone crop about every three years. Of course, the abundance of the seeds the trees produce also depends on the right weather and growing conditions.
Pine siskins, common redpolls, and red crossbills are food nomads throughout the year. If they find a good all-you-can-eat spot, they camp out. Pine siskins and red crossbills even build their families based on when and where food is plentiful. Pine siskins may start nesting as early as February or as late as July, depending on food. Red crossbills are even more free about starting families, nesting when they have a plentiful food supply regardless of the season. In both species, the female doesn’t leave the nest during incubation and the male brings food to her so the eggs are always warm. Unlike other songbirds, males defend only their mate and nest, not a whole territory. Males even go out in flocks “with the guys” for a meal. Which makes sense — if food is plentiful, why fight over it?
How do these birds know where the eatin’ is good? They communicate. For example, if red crossbills flying overhead hear the calling of a flock feeding, they may join the party. When the flock moves to a new tree, a crossbill flock stays quiet at first, testing out the fare. Birds that aren’t finding enough seeds may start to call. If only a few birds complain, but others are busy with full beaks, the flock continues feeding. If more and more birds start calling, indicating a second-rate restaurant, the noise builds to a crescendo and the flock departs.
Although they all eat seeds, there are differences in each species’ diet. Pine siskins have the smallest, slimmest bill of the three. They eat the seeds of grasses, annual plants, and trees such as alders and some conifers. Siskins sometimes hang from the tip of a cone, even trying to wedge open the scales of a closed cone, but they aren’t as efficient as crossbills. Their bills aren’t strong enough to open tough shells of food such as sunflower seeds, but they may sift through pieces left by other birds at feeders.
Common redpolls have a conical beak, stouter than the pine siskins’, although still short. They prefer small seeds, such as those from an alder or conifer. These tiny gymnasts sometimes hang upside down or balance on thin twigs to snag seeds. Redpolls are able to survive even the cold winters of the Interior with a couple specializations. One is they have no qualms about being active in low light; I’ve heard their chatter at a feeder even before dawn.
Another very interesting adaptation, shared by siskins, is that redpolls can store food in their crop, a pouch in the esophagus. This way the redpolls can grab more seeds at a feeder — even though they may not have to shell them immediately— maximizing the efficiency of gathering seeds, while minimizing the time they are exposed to predators or to windy, cold conditions. They regurgitate the seeds later at a covert location, shelling and swallowing the meal at their leisure. This is especially useful at the end of the day when redpolls face a long night trying to stay warm. They gather as many seeds as they can and eat them later, so they don’t have to wait so long between meals.
Red crossbills are the most specialized of the bunch, eating mainly conifer seeds. A crossbill feeds on cones with open scales if available, but otherwise tackles closed cones, sometimes even snipping one at the stem so it can manipulate the cone. The curved tips of the upper and lower parts of a crossbill’s stout beak grow past each other, crossing like tongs. The bird wedges its bill in between two scales on the closed cone, pushing sideways with the bottom part of the bill in the direction it crosses outward. The bottom of the bill pushes against the scale closest to the tip of the cone, and the upper part of the bill against the overlapping scale closer to the bottom of the cone, prying the scales apart. Sometimes the crossbill twists its head for a particularly tricky cone, giving the bird extra leverage to open the scales until it can remove the seed with its tongue.
Although it may seem wasteful that crossbills don’t eat all the seeds in a cone, it’s actually a matter of efficiency. Crossbills pluck out the biggest, easiest seeds on a cone and then move on to the next one. They leave behind the smallest seeds in the hardest-to-open sections of a cone because it isn’t worth the energy needed to extract them. This way they can make the most of their time at the dinner table.
So keep your feeder stocked, even if it seems deserted. You never know when you’ll have a large flock of unexpected guests.
• Beth Peluso is a freelance writer and illustrator and avid birder. She enjoys spying on wildlife across Alaska.