a common bird with an uncommon memory

A friend and I stood in a small muskeg on Douglas, checking out some deer tracks, when little twitterings announced the arrival of chickadees. Two of them scoured the twisted trunk of a dead pine right next to us, but we soon saw that there were two more—no, four more—no, maybe six or eight more—thronging the foliage of nearby hemlocks. They might be finding overwintering spiders or insect pupae and even adults.

I enjoy watching the flock that hang out around my house, too, as they diligently pick out little black sunflowers seeds from the feeders and flit into the adjacent spruces. They may eat some of those seeds immediately but sometimes the return trip to the feeder happens so quickly that there was only time to stash the seed in a hand crevice for a later snack.

Watching these chickadees stirred me to dig for more information. The species that lives in our area is the chestnut-backed chickadee, which lives principally in the Pacific coastal rainforest. Of the seven species of chickadee in North American, four (including ours) breed regularly in Alaska.

Chestnut-backed chickadee. Photo by Bob Armstrong

All the chickadees share the habit of nesting in tree cavities. The cavities may be natural ones left by a broken branch or a woodpecker, or they may be excavated in soft, decaying wood by the chickadees themselves. Clutch sizes tend to be large, averaging seven or eight eggs per nest. Both parents care for the chicks, but in some cases, not all the chicks in a nest have the same father because, as in many other birds, some hanky-panky goes on! Predation on nest contents of cavity-nesting birds is commonly lower than for open-cup nesters, but nest predation on chestnut-backed chickadee nests can be as high as fifty or sixty percent of nests; red squirrels are a principal predator on eggs and chicks.

When chickadees forage through the canopy, they often hang upside down to glean from the undersides of twigs and leaves. They can do this very agilely, reportedly thanks to well-developed special leg muscles. Chestnut-backs often forage in flocks in winter, sometimes joined by other species such as nuthatches and kinglets. In the southern part of their geographic range, as many as fifteen other species have been recorded in mixed-species flocks with chestnut-backs.

Where chestnut-backs overlap with black-capped chickadees in Washington, their foraging patterns differ slightly. Chestnut-backs have slightly smaller bills and are more closely associated with conifers. They forage especially on foliage and twigs, while the blackcap forages more often on the bark of tree trunks and branches. Although both of them hang upside down to reach the undersides of leaves, the blackcap reportedly does so more often.

Chestnut-backs apparently have been much less intensively studied than blackcaps, which is arguably the best-studied songbird in North America. Because detailed information about chestnut-backs is hard to find, I thought I’d summarize some of the details about blackcaps, which range all across North America and nest in the Interior of Alaska. It seems likely that much of what is known about blackcaps also applies to chestnut-backs, but that remains to be ascertained. In the meantime, here is some cool stuff on blackcaps, particularly their winter flocking and its consequences, food storage behavior, how they get through the cold season, and their calls.

The winter flocks of black-capped chickadees are strongly hierarchical, with males generally dominant to females and older birds dominant to younger ones. Winter ranks have carry-over effects to the subsequent breeding season. Dominant male breeders are in better body condition than subordinates and tend to have better nesting success, at least in some habitats. They also participate more than subordinates in hanky-panky outside of the socially monogamous pair. Higher winter ranks of females also lead to their better survival in the breeding season.

Black-capped chickadees store food in fall and winter, each one stashing hundreds and sometimes thousands of seeds and insects in bark crevices or among conifer needles or in cracks in trunks and branches. Unlike red squirrels, which create piles of cones, the chickadees generally store items singly. They are very good at remembering where these items are stashed, being able to retrieve them after several days or even weeks, if one of the many potential thieves (squirrels, mice, nuthatches…) has not stolen them.

The part of the brain associated with memory is called the hippocampus, which increases in size in the fall, when food storage is a common activity. Blackcaps in the north store more food and have larger hippocampi than those in the southern part of their range. Blackcaps also have larger hippocampi than chickadee species that do less food storage.

Dealing with cold winter temperatures requires metabolic energy, and the colder the weather, the higher the metabolic costs. Blackcaps in Alaska are reported to have a metabolic rate about fifteen percent higher than those farther south. Heat generated by the muscular activity of foraging, during the day, also contributes to staying warm on winter days. At night, however, blackcaps allow their body temperatures to drop ten or twelve degrees centigrade, saving substantial energy; however, the blackcaps in Alaska are a bit different (of course?), and only let their temperature drop about three degrees. At night, they roost in cavities or in thick vegetation, usually singly.

The calls of black-capped chickadees may sound to us like indistinguishable twitterings. But not so, among themselves. They can distinguish the subtle variations in each other’s calls and identify specific individuals (as can many other songbirds). Furthermore, the “chick-a-dee” alarm call varies according to the relative risk from a potential predator that is visible; a different call indicates a predator that has been heard. Other species, such as nuthatches, eavesdrop on blackcap alarm calls and respond to the signal. Recent research has shown the male black-capped chickadees sing at higher pitches when the level of anthropogenic noise is high (for example, near heavy traffic, construction, logging activity, and so on), which may have consequences for breeding (as it does in some other songbird species too).


Canada geese

many subspecies, habitats, and sizes

A favorite sign of spring is a flight of Canada geese, winging northward in the familiar V- formation, talking to each other as they go. I hear them coming, tip my head back, and wait—and then there they come. Gradually the melodic calls fade away in the distance. There’s nothing quite like it!

A migrating flock of Canadas is a very familiar sight for many people. So perhaps it is not very surprising to hear someone say, as we are driving down Egan over Lemon Creek, “Oh look, the geese are back!!” But the geese seen there and elsewhere on the wetlands in winter and early spring are not migrants. They can be found somewhere on the wetlands at any time during the winter; an estimated five or six hundred Canadas spend the winter with us.

Vancouver Canada Geese in flight. Photo by Bob Armstrong

These geese belong to a coastal subspecies, whose geographic range roughly coincides with the coastal rainforest. They are considered to be non-migratory, although these birds may make short-distance movements at certain seasons.

Of course, we have some migratory Canadas too, in season. One subspecies nests chiefly on the Copper River Delta, and passes through here, to and from its wintering grounds a little farther south. Another subspecies nests in the Interior, and part of that population winters in California, coming by us in spring and fall. In addition, there is the small Cackling Goose, which looks like a miniature Canada Goose but is now considered to be a different species; it can occasionally be seen here as it flies between western Alaska and California.

The entire species we know as Canada goose is widespread in North America. It is divided into several (or many, according to some researchers) subspecies. The birds of some subspecies are very large; for example the one that uses the Mississippi flyway averages maybe 4500g (almost ten pounds). The Cackling Goose is quite small, averaging roughly 1600g. Our resident birds, known as the Vancouver Canada goose, are intermediate in size, averaging over 3000g.

The Vancouver Canada geese nest in rather dense rainforest, unlike most other subspecies, which typically use open habitats near water. Vancouver Canadas usually place their nests on the ground (as do other subspecies), but sometimes the nests are on snags or in trees, as much as 15 m above the ground. Some nests are in muskegs, and many nests are relatively close to muskegs and small pools of standing water. Nests are not necessarily close to ponds or lakes.

Male and female form a long-term pair bond, spending their lives together. During the month-long incubation period, when the female is incubating, the male commonly perches high in nearby trees, standing guard. Clutch sizes vary greatly, but often there are three to five eggs; older females usually lay larger clutches and larger eggs than young females.

Broods of Vancouver Canada geese use dense understory as escape habitat when threatened by potential predators. This is quite different from other subspecies, whose nests are commonly close to water and whose broods typically flee to open water. As the rainforest goslings grow, they are found more often in open habitats, not necessarily near the nest site. They often band together with other broods in crèches, which are thought to reduce the risk of aerial predation. Young birds stay with their parents though the winter.

Nest success can vary enormously, depending on weather and predator activity. For the rainforest subspecies, and for the species as a whole, as few as 25% of nests may be successful in producing goslings, but in good conditions, sometimes over 80% of nests are successful. Cold, wet weather is deleterious to nest success, and areas with many predators (for example, foxes, coyotes, ravens, mink, bears) may lose most of the nests. The age of the female also matters: older females are generally more successful than younger ones.

Although the geese may mature at an age of two years, some do not mature until they are three years old. If they are lucky, they may reproduce for several years.

After the nesting season, in late summer, Canada Geese molt their worn flight feathers, so for three or four weeks they cannot fly. In preparation for molting, Vancouvers typically move relatively short distances to selected, protected bays and inlets, where foraging is good. There they grow their new flight feathers in relative peace. Wachusett Inlet in Glacier Bay is one of molting sites; if you kayak into this inlet just after molting time, the water surface is covered with goose feathers.

Canada Geese are herbivores, grazing on many kinds of plants in the course of a year. The Vancouver Canada Goose likes skunk cabbage leaves in the nesting season; one can often see the bite marks on the standing leaves. They also eat blueberries, lingonberries, and crowberries in season. In late winter and early spring, the Vancouvers often forage on the roots and young shoots of sedges in the wetland. Most goose foods are not highly digestible or high quality, and the digestive processes of geese are reported to be moderately inefficient, so geese need to eat a lot. There are reports that they may sometimes snack on small clams and worms, drifting salmon eggs, and even dead salmon.

The need to eat large quantities of vegetation means that geese spend a lot of time just eating. A group of foraging geese usually has one or two individuals standing upright, as sentinels, to warn of approaching danger. If wandering people or dogs come too close, the flock will take off and seek a less disturbed foraging area. Flight is expensive, and the more the birds are disturbed, the more food they need to pay the costs of flight. So frequent disturbance makes it hard for them to get enough food.

During the hunting season on the Mendenhall Wetlands, geese become very wary and easily disturbed. In fact, observers have noticed that geese (and ducks) often leave the wetlands during the day and fly to Auke Lake, in order to avoid the hunters. They come back to the wetlands at night to forage. Unfortunately, these daily flights cross the paths of approaching airplanes—not good for either goose or plane!