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Posts Tagged ‘Carduelis tristis’

Black-capped Chickadee (Poecile atricapilla)

The most amazing thing about the little birds that visit the feeder is that they can survive at all. Scarcely more than tiny puffs of feathers and a heartbeat, how do they do it? In fact, they have a number of coping mechanisms, both behavioral and physiological, that help them make it through the winter.

The chickadee, for example, changes its diet. In the summer, chickadees prefer insects and other invertebrates, but in the winter, they change to a predominantly seed diet. Seeds may be a more clumped resource, and seeds tend to have a higher fat content than animal matter in winter, thus reducing the physical costs of foraging. Chickadees also cache seeds against periods when food is hard to find. See A Chickadee Never Forgets for more on this.

When it comes to staying warm, size does matter. Conservation of heat can be maximized by minimizing the surface-area-to-volume ratio. Thus, animals in cold climates tend to be bigger than their southern relatives (Bergmann’s rule). An example is the polar bear, which is larger than black bears that live farther south. In this, little birds are at a disadvantage. Species such as chickadees are distinctive for having the highest ratios of feather weight to body mass, averaging 10 to 11% compared to an average of 6 to 8% for other avian species. Also, chickadees have a prolonged molt after the breeding season, which ensures less feather wear and thus greater insulation at the beginning of the winter.

American Goldfinch (Carduelis tristis)

In winter, night may be the most difficult time for most small birds because of its colder temperatures and length, combined with a relatively short daylight foraging period. Physiological adaptations allow winter-acclimatized goldfinches to maintain a constant 40° body temperature for up to eight hours at -70° C. To maintain their body temperature in such extreme cold, they shiver intensely and produce heat at a rate four to five times their basal rate. This high level of thermogenic endurance is seasonal. Summer-acclimatized goldfinches cannot maintain normal body temperature for more than an hour in such frigid temperatures.

Chickadees have a different strategy. They utilize a period of regulated hypothermia at night, letting their body temperature drop by as much as 10° C. This reduction in body temperature lowers the metablolic expenditure for the night by as much as 23%. The benefit of this strategy decreases as the size of the bird increases. Large birds would require too much enegy to reheat their bigger bodies to use this system.

The elevated metabolic rates that small birds must maintain through cold nights place a premium on energy reserves. These reserves consist primarily of the undigested food in the crop and other parts of the digestive tract, and fat. Some birds begin roosting with relatively large amounts of seed in their crops. However, the primary energy reserve for most species is fat. In winter-acclimatized goldfinches, fat stores at the onset of roosting are significantly higher than in summer, and may reach 15% of lean body size.

It’s all pretty amazing, but I’m glad I’m inside, sipping hot chocolate and thinking about those poor goldfinches, shivering in the night.

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Dinner is served. Breakfast and lunch, too! With cold weather approaching, I have been getting my bird feeders cleaned and set up for the winter. Birdwatchers can be an obsessive group, keeping a life list, hiking for miles to see that one special species. For the most part, I am satisfied just to let the birds come to me and watch them from the comfort of my home. Especially in winter, when it’s cold and snowy.

Feeding backyard birds has become a hugely popular hobby across North America, second only to gardening. It’s estimated about 1/3 of households make seed available. Considering the huge negative impacts humans have on the lives of birds, the occasional free lunch seems like the least we can do for them.

Supplemental feeding may help weaker birds make it through the winter and allow birds to begin the breeding season in better condition. During extreme cold spells, feeders can help more birds survive as individuals who are unable to find sufficient food before sunset often don’t make it through the night. Feeding birds will not stop individuals from migrating, an urge triggered by daylength. However, over time the availability of widespread supplemental food supplies can impact the winter range of birds. In past decades, the number of goldfinches overwintering in Ontario has grown. Northern Cardinals have also been able to expand their range northward partly because of bird-feeding practices.

I set my feeders up farther away from the house than I would have liked. It’s nice to have the birds arriving just outside your picture window. But proximity to a window can be a deathtrap for birds, who often take off in a rush when startled and fly right into the window. Many birds die this way every year. If the impact doesn’t kill them outright, they may die later from internal bleeding. Placing the feeder away from the house makes viewing less immediate, but is safer for the birds.

Having a variety of feeder types and different kinds of seeds available helps to attract an assortment of species to your yard. As the weather has been unseasonably mild, so far I have had a limited number of visitors, but a steady stream of Blue Jays (Cyanocitta cristata) stop by. I put a handful of peanuts in the shell out for them, a sure hit. While the mainstay of my sunflower offering is black oiled sunflower, I also put out some of the larger striped sunflower for larger birds like the jays.

I have a couple of kinds of suet feeders. This log variation has been quite popular. Here, a Downy Woodpecker (Picoides pubescens), identifiable as a male by the red spot on the back of his head, is helping himself. If you are a keen observer, it is possible to tell woodpecker individuals apart by the pattern of colouration on their heads.

By far the most numerous visitors at the feeders right now are American Goldfinches (Carduelis tristis). When I first started feeding winter birds a few decades ago, I was puzzled by these drab, olive-yellow visitors. It was a while before I learned that the bright yellow summer birds molt into a less flamboyant feather coat for the winter. Losing their breeding colours helps to signal male birds that breeding competition has ended and lets them come together as a flock. If you want to attract goldfinches, a nyger feeder is your best bet. Goldfinches love nyger (thistle) seed, but also take black oiled sunflower seed.

Another common visitor is the Black-capped Chickadee (Parus atricapilla). In fact, these jaunty, active little birds are often the number-one most-common feeder bird at Ontario feeders. Chickadees like black oiled sunflower seed, and I usually put out a handful of peanut bits or small redskin peanuts for them as well. They have to beat out the blue jays though.

Most feeder birds visit multiple backyards and still use natural food sources as well, so unless you are in an isolated location, you can take a winter vacation without guilt over hungry birds. One uncomplicated argument for feeding birds goes like this: When you feed birds, you help more birds survive to breed again. More birds will eat more insects, so fewer pesticides are needed. Fewer chemicals are safer for everyone.

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Once the trees drop their leaves, the nurseries that cradled the year’s bounty of baby birds are suddenly revealed. It’s amazing how well-concealed nests are during the summer. Of course, if you pay close attention to the actions of birds, and know where to look, it is possible to find their nests while they are active. However, I have been content to let the birds live their lives in my yard without my scrutinizing of their comings and goings to closely. Consequently, I have daily walked right past nests without knowing they were present until the fall.

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Many American Robins (Turdus migratorius) build their nests close to our house in trees and hedges bordering the lawn and driveway. Robin nests are among the easiest nests to identify in the fall. Robins construct very sturdy nests, weaving grasses into a cup and plastering the walls with mud. They are the only builders of cup-shaped nest to employ mud in this fashion, so dried-mud is a pretty sure sign that you are looking at a robin’s nest. The nest pictured at the top of the post was built in a hawthorn tree. The nests above and below are further examples of robin architecture.

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The robin who built the nest below included some twine in the construction.

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This nest, located in a Amur Maple tree, features a strip of torn plastic. The mud isn’t conspicuous, but I got out the ladder and climbed up to take a closer look. Sure enough, the mud rim can readily be observed. For more on robin nests, see Robin’s Egg Blues.

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robinnest

Another readily-identifiable nest to be found in the bare tree branches is that of the Baltimore Oriole (Icterus galbula). Orioles weave a hanging basket that is typically secured at the rim or edges to a drooping branch. It is woven with various plant fibres and lined with fine grass, hair or plant down. The nests often hang in branches over roads, an adaptation, perhaps, of an instinct to build the nest over flowing water. The nests quickly become weather-worn once the trees lose their leaves.

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Many nests are difficult to identify once their occupants have departed. Here is a nest with a scenic situation over water. It may have been built by an Eastern Kingbird (Tyrannus tyrannus). Kingbirds like to nest on a horizontal tree limb, about halfway between the tree trunk and its canopy. About 25 % of the time, the nest is located over water. Kingbirds build a bulky, untidy nest using weed stems, grass, plant down and rootlets.

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The nest below is likely that of an American Goldfinch (Carduelis tristis). Goldfinches prefer to build their tightly-woven nest in a branch fork. Caterpillar webbing and spider silk is often used to bind the outer rim of the nest.

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The builder of this large nest, over a foot across and high up in a larch tree, remains a mystery.

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Not all the nest-builders were birds. This nest, possible belonging to Bald-faced Hornets (Dolichovespula maculata), has already started to disintegrate.

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The last day of March was dull and gray. At least it wasn’t actually raining, as it was over the weekend. The river level is quite swollen from the recent downpour. But no ice! March left as it came in, like a lamb. The month seemed to go by quickly, carrying us ever closer to warm weather.

goldfinches

The last redpoll was spotted on Saturday. They have headed back to their northern breeding grounds. A few pine siskins linger, but the niger feeder has mostly been taken over by American goldfinches (Carduelis tristis). No doubt the goldfinches were happy to see the last of their pushy, querulous cousins. The goldfinches are getting ready for the breeding season too. The males at the feeder look decidedly ratty as their new bright yellow summer feathercoats grow in.

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The garden will be a surprise this year, as I wait to see what previous owners have planted. There are no bulbs showing their heads, but a sedum (maybe Autumn Joy), above, is pushing up shoots.

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The blades of iris leaves are growing.

hellebore

A hellebore is struggling to flower. It appears that someone dumped sand over it last fall, thus retarding its growth this spring.

March brought no more than a sprinkling of snow. As we begin April, hopefully I am done with the snow shovel for another year (the new, blue, Christmas snow shovel). Still, I though twice about putting it away. I’ve left it at the ready, just in case Winter isn’t done with us yet. Just in case Winter has one more last-minute snow storm up his sleeve. Why tempt him?

shovel

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