Chickadees

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.

banded-chestnut-backed-chickadee-in-flight-by-bob-armstrong
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).

Bearings on bears

the advantages and disadvantages of being a big bruin

In the world of North American bears, there are considerable advantages to being big. The biggest males generally mate with more females than medium size or small males do. For example, one study found that three large male black bears encountered more than twice the number of females in the breeding season as several smaller males did, and a much higher proportion of these encounters were with receptive females. As a result, the three big males fathered ninety-one percent of the cubs. Being big led to winning more face-offs and fights with other males and perhaps also to being favored by females. Big males are also able to dominate smaller bears and gain almost exclusive access to important food resources in many situations.

Being big also has pay-offs for females. They too are more likely to win threatening encounters with other bears (when they can’t be avoided). Moreover, big females are likely to produce more cubs than smaller females. Research has shown that fat females produce more surviving cubs than less-fat females, because they have more energy for producing milk to feed their new cubs, born during hibernation. Although both small and large females can be fat, large females have better access to food resources, because they can dominate smaller bears, and they can carry more fat on their large frames.

brown-bear-with-fish-haines-jos
Photo by Jos Bakker

Here in Southeast, researchers suggest that access to spawning runs of salmon in late summer and fall allows bears to become both bigger and fatter than bears that don’t have access to salmon. Eating meat, especially salmon, seems to allow bears to grow extremely big. However, some bears in Southeast don’t come to the salmon runs, staying instead in the alpine zone. Apparently they give a higher priority to avoiding the risks of encountering dominant bears that rule the salmon streams, and they probably have lower reproductive success. Spawning runs of other fishes offer foraging advantages to hungry bears too: It would be interesting to learn if the grizzly bears feeding on the spawning runs of broad whitefish in the Mackenzie River in the Northwest Territories get bigger and fatter than those without access to the runs.

Being big has its advantages, certainly, but there is also a ‘down side’ to large size. Big bears can’t run as fast as smaller ones, and researchers suggest that they are more likely to hunt by ambushing prey rather than pursuing it. Big bears can climb trees but they are much less agile in doing so than smaller bears. Trees offer refuge, especially to smaller bears, from other, larger bears. Tree climbing also gives agile bears access to food in some cases. For example, in spring black bears forage on cottonwood flowering catkins and young seed pods; near the Visitor Center they sometimes strip the trees of most of their branches in order to reach the catkins and pods. A really big black bear would have trouble clambering up many of the middle-sized cottonwoods up by the Visitor Center to gather the edible catkins, but the smaller bears do so with apparent ease. Later, in the summer, both black and brown bears in Southeast climb wild crabapple trees to get the fruit; outside of Southeast, bears climb (or did so before they were exterminated in many states) many kinds of trees to reach the fruit.

Big body size also makes it difficult to gain weight in preparation for hibernation by eating vegetation alone. Putting on fat is necessary for survival during the long months of hibernation and for females to produce milk to feed their cubs. Although our bears commonly eat a lot of green plant food, they can’t digest plant fibers. So apparently big bears just can’t get enough nutritious plant material to put on the necessary weight. Very big bears probably also have difficulty gaining weight on a diet of berries, except perhaps in really good ‘berry years.’ It could be argued that the bigger the bear, the more meat it needs to eat; and conversely, meat eating is necessary to achieve large size in the first place.

Being big has another major disadvantage: Hunters often take pride in killing large animals, be they sheep or goats or bears. So trophy hunting imposes a risk on large body size. The consequences of removing large, dominant individuals from a population are well understood (but commonly ignored): loss of the large individuals upsets to social organization and probably increases the risk of infanticide by previously subordinate male bears (killing cubs tends to bring the female back into breeding readiness). More mating by smaller bears eventually results in a population of smaller bears, because the genes for large size become less common in the population.

Spatial overlap between bears and humans

how can we all get along?

mary-and-bear
A neutral bear encounter. Photo by

Coastal Alaska supports both black and brown bears, both of which inhabit the rainforest and potentially eat much the same kinds of food. Where they occur together, how do they get along?

In Southeast, both species occur in many areas, and one can watch both species fishing for salmon in places such as Anan Creek. Here the black bears tend to avoid the brown bears, but there are usually so many salmon that both kinds of bears feed well. But that is not always the case.

Brown bears achieve larger body size than black bears of the same age and gender. Larger body size allows brown bears to be dominant over black bears and potentially to exclude them from choice feeding areas. Salmon spawning runs are prime foraging places and brown bears are often capable of near- monopolies there. One study near Denali found that brown bears ate much more salmon than black bears, in general, and when salmon runs were poor, black bears got no salmon at all because brown bears prevented access to the streams. So in years of small salmon runs, black bears had poor body condition and poor reproduction.

Another study, on the Kenai Peninsula, also found that brown bears ate far more salmon than black bears. Occasional male black bears visited salmon runs but obtain few fish and no female black bears had access to the stream. Both species of bear ate berries extensively, but fruits made up a higher proportion of energy intake for black bears. Part of the Kenai Peninsula apparently lacks brown bears, for some reason, and in that area, black bears normally consume lots of salmon.

Although both species of bear occupy much of Southeast, there are broad areas where only one kind of bear has well-established populations. On Admiralty, Chichagof, and Baranof islands, only brown bears occur. But why, given that they co-occur with black bears in other areas? On the other hand, on the islands south of Frederick Sound, including Haida Gwaii, only black bears are found. However, fossil remains show that brown bears formerly occurred there , and brown bears are seen there upon occasion even now, but they do not establish breeding populations. Why are the browns absent in these regions? Selective hunting? Some subtle habitat change? An interesting puzzle.

Humans now occupy significant chunks of coastal Alaska, largely displacing bears from most urban and agricultural areas. Rather than deal here with the obvious issue of habitat usurpation by humans, I’d like to focus on the possible effects of hunting and bear-viewing activities. Human hunting pressure might change interactions among bears, if it is focused on one gender or if it significantly reduces bear density. In addition, we have so many bears that bear-watching has become a profitable business as well as a popular activity for local folks.

A study in south-central Alaska found that where brown bears are not hunted, males clearly dominate at most fishing sites except when fishing is poor; at good fishing sites, males were far more common than females. Big bears need to spend more time fishing to get enough fish to eat; fishing is very inefficient for them when capture rates are low. However, where bears are hunted, male brown bears were not more common than females at good fishing places. Hunting pressure is heavier on males than on females, reportedly, which would reduce their numbers. In addition, where they are pursued, males may become more wary than females, such that they sacrifice good fishing for perceived safety. Whatever the reason, fewer males meant that females, especially those with cubs, had more access to fishing sites.

Add bear-viewing humans into the mix of interactions, and researchers found that adult male brown bears tended to avoid the humans, showing more avoidance in areas where hunting pressure was higher. Males also avoided humans more when there were alternative foraging sites in the same region, but if there were no alternative sites, male tolerance of human viewers increased—and presumably females then got fewer fish.

A study in British Columbia found that females with cubs spend less time fishing when big males were active; these females had about a third less consumption of salmon than undisturbed females. Bear-viewing activity tended to displace the big males, providing mother bears with increased access to fish. Mere presence of humans had little effect on foraging of females.

Near the Mendenhall Visitor Center, most of the black bears that use the area are females and young bears; there are few adult males. Observers believe that here, too, bear-viewing humans provide smaller bears with a safe area to forage, where they are not displaced by big males. It would be interesting to learn where the adult male black bears in this region go to forage! At Pack Creek on Admiralty Island, most of the brown bears foraging on salmon in the estuary near the viewing area are females and subadults, and that the males tend to forage farther upstream, away from most humans. On Admiralty, hunting is generally harder on brown bear males than females, especially in spring, so perhaps males are rightfully more wary.

Thus, the general consensus seems to be that females avoid big males when they can and take advantage of their absence when possible, including finding temporary refuge near bear-viewing activities on humans.

Spatial overlap among bears…

…and between bears and humans

Coastal Alaska supports both black and brown bears, both of which inhabit the rainforest and potentially eat much the same kinds of food. Where they occur together, how do they get along?

In Southeast, both species occur in many areas, and one can watch both species fishing for salmon in places such as Anan Creek. Here the black bears tend to avoid the brown bears, but there are usually so many salmon that both kinds of bears feed well. But that is not always the case.

Brown bears achieve larger body size than black bears of the same age and gender. Larger body size allows brown bears to be dominant over black bears and potentially to exclude them from choice feeding areas. Salmon spawning runs are prime foraging places and brown bears are often capable of near- monopolies there. One study near Denali found that brown bears ate much more salmon than black bears, in general, and when salmon runs were poor, black bears got no salmon at all because brown bears prevented access to the streams. So in years of small salmon runs, black bears had poor body condition and poor reproduction.

Another study, on the Kenai Peninsula, also found that brown bears ate far more salmon than black bears. Occasional male black bears visited salmon runs but obtain few fish and no female black bears had access to the stream. Both species of bear ate berries extensively, but fruits made up a higher proportion of energy intake for black bears. Part of the Kenai Peninsula apparently lacks brown bears, for some reason, and in that area, black bears normally consume lots of salmon.

Although both species of bear occupy much of Southeast, there are broad areas where only one kind of bear has well-established populations. On Admiralty, Chichagof, and Baranof islands, only brown bears occur. But why, given that they co-occur with black bears in other areas? On the other hand, on the islands south of Frederick Sound, including Haida Gwaii, only black bears are found. However, fossil remains show that brown bears formerly occurred there , and brown bears are seen there upon occasion even now, but they do not establish breeding populations. Why are the browns absent in these regions? Selective hunting? Some subtle habitat change? An interesting puzzle.

brn-bear-in-glacier-bay-jos
Brown bear in Glacier Bay. Photo by Jos Bakker

Humans now occupy significant chunks of coastal Alaska, largely displacing bears from most urban and agricultural areas. Rather than deal here with the obvious issue of habitat usurpation by humans, I’d like to focus on the possible effects of hunting and bear-viewing activities. Human hunting pressure might change interactions among bears, if it is focused on one gender or if it significantly reduces bear density. In addition, we have so many bears that bear-watching has become a profitable business as well as a popular activity for local folks.

A study in south-central Alaska found that where brown bears are not hunted, males clearly dominate at most fishing sites except when fishing is poor; at good fishing sites, males were far more common than females. Big bears need to spend more time fishing to get enough fish to eat; fishing is very inefficient for them when capture rates are low. However, where bears are hunted, male brown bears were not more common than females at good fishing places. Hunting pressure is heavier on males than on females, reportedly, which would reduce their numbers. In addition, where they are pursued, males may become more wary than females, such that they sacrifice good fishing for perceived safety. Whatever the reason, fewer males meant that females, especially those with cubs, had more access to fishing sites.

Add bear-viewing humans into the mix of interactions, and researchers found that adult male brown bears tended to avoid the humans, showing more avoidance in areas where hunting pressure was higher. Males also avoided humans more when there were alternative foraging sites in the same region, but if there were no alternative sites, male tolerance of human viewers increased—and presumably females then got fewer fish.

A study in British Columbia found that females with cubs spend less time fishing when big males were active; these females had about a third less consumption of salmon than undisturbed females. Bear-viewing activity tended to displace the big males, providing mother bears with increased access to fish. Mere presence of humans had little effect on foraging of females.

Near the Mendenhall Visitor Center, most of the black bears that use the area are females and young bears; there are few adult males. Observers believe that here, too, bear-viewing humans provide smaller bears with a safe area to forage, where they are not displaced by big males. It would be interesting to learn where the adult male black bears in this region go to forage! At Pack Creek on Admiralty Island, most of the brown bears foraging on salmon in the estuary near the viewing area are females and subadults, and that the males tend to forage farther upstream, away from most humans. On Admiralty, hunting is generally harder on brown bear males than females, especially in spring, so perhaps males are rightfully more wary.

black-bear-with-salmon-by-bob-armstrong
Black bear at Mendenhall Glacier. Photo by Bob Armstrong

Thus, the general consensus seems to be that females avoid big males when they can and take advantage of their absence when possible, including finding temporary refuge near bear-viewing activities on humans.