Posts Tagged ‘winter’

Bulking Up

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Tuesday, October 25th, 2011

I spot the animal along a roadside in a national park, a glimpse of something large and dark, rustling in the undergrowth. The highway is devoid of oncoming traffic, so I whip a quick U-turn for closer inspection. Mystery solved. Planted on all fours near the roadside is an American Black Bear.

Parked, with full attention to focus on the bruin, I realize the animal is frenetically mouthing and mauling a bush for its berries. Although midday, the bear is feeding as frantically as one of my teenage sons after missing three meals. It’s late summer, a time of bounty. Ripe berries abound. There are lots of nutritious insects and scores of rodents and other mammals for Blackie to hunt, not to mention a bounty of roots and plants. All of these things are palatable to a black bear, perhaps the most omnivorous creature in North America. Why is it attacking this berry bush as if it may be its last meal?

In contrast to humans seeking to shed a dozen unwanted pounds, Blackie is bulking up. Yes, there’s plenty to eat at the moment. But in its haunts here in the northern Rockies, this black bear will retire to a den soon, spending the entire winter underground. To maintain the energy needed to survive its hibernation, the bear relies on fat. The typical black bear loses around 30% of its body weight during hibernation.

In late summer and fall, instinct propels black bears to bulk up. They eat ravenously and nearly continually when food sources are available. At this time, bears prefer high-calorie foods that convert easily to fat such as nuts and berries. Has our bear missed a meal? Probably not. It’s just bulking up for winter.

Many biologists believe humans have some innate potential for hibernation, just like bears. From now until November, if you catch me pigging away at the all-you-can-eat buffet, I’m not over-indulging, just preparing for winter.

Winter Owls

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Tuesday, March 1st, 2011

The great thing about winter owls is that in a good year they can be easily spotted. Unfortunately, this hasn’t been a particularly good year.
Once they come out of the boreal forest in the late fall, Great Gray Owls, Snowy Owls and Hawk Owls pretty much stay put wherever they settle for the winter. And they are diurnal – they hunt during daylight hours. So, if you get a report from someone that there’s a winter owl at a certain spot, you can bet that it’ll probably be there or nearby.
The number of Great Gray Owl reports near Winnipeg this winter is not very high, relative to previous years; I’ve heard that they’ve been seen, but I haven’t been able to get out to tick them off my winter list.
According to Dr. Jim Duncan, wildlife biologist and owl expert, low numbers of Great Grays in the past have coincided with years with thicker snow cover (>180 cm). That’s been the case this winter. Thick snow cover reduces the number of predators that ordinarily feast on meadow voles, their main prey. With their unmatchable sense of hearing, Great Grays have no problem detecting small mammals even under a thick blanket of snow. So, fat healthy (radio-marked) Great Grays are staying back in the boreal forest.
In my neck of the woods Snowy Owl numbers are low this winter as well. But if you check the electric transmission poles and fence posts on major routes in and out of the city, you can almost be assured of finding a couple. We’re nowhere near the record year of 2001 when one party counted 55 Snowies in one day southwest of Winnipeg. It used to be thought that these tundra natives irrupted when the lemming populations of the north plummeted. That simple theory has since been disputed, though there’s some indication that crashes in lemming numbers can account for early arrivals.
Hawk Owls are more easily found this year. They’re not as widespread as they were in 1996-97 when more than 50 were spotted and even I counted a couple of dozen on one outing. And few have ventured into my suburban neighborhood as one did a couple of years ago. I saw that bird every day on my way to and from work usually sitting on the bent-over top of a small spruce tree. Their long tails, big yellow eyes, and non-erect posture make them easy to identify.
Jim Duncan believes that Hawk Owls have clearly had a good breeding season somewhere within a 1,000 mile radius (their normal yearly range) of Winnipeg. That may account for their numbers. All the Hawk Owls he’s encountered thus far have Hatch Year 2010 birds, and they are in excellent condition. One Hawk Owl weighed a whopping 435 grams, possibly the heaviest he’s caught to date. So, they’re not coming here because they’re hungry.

Pinecones on a Willow Tree?

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Thursday, January 20th, 2011

Have you ever seen pinecones on the end of willow branches? They aren’t really pinecones, they are protective homes for the Pinecone Willow Gall-midge (Rhabdophaga strobiloides), a type of fly that relies on willows for its home.

The adult gall-midge lays its egg on the tip of a willow branch as the terminal buds begin to swell in the early spring. The egg, and larva that hatches, release a chemical that tricks the growing willow leaves into forming a structure that looks superficially like a pinecone made of overlapping leaves.

As the larva feeds the bud ceases to develop, but the plant still directs nutrients to the tissues. Biologists working at the University of Michigan Biological Station at Pellston, Michigan found that somehow the gall-midge manipulates the willow to provide resources from other places in the plant to the gall for them to continue to feed and survive. They found that galled twigs compared with normal twigs had greater growth in twig girth than when no gall is present and twigs with galls grew equally well with or without leaves.

The bud continues to swell as the larva feeds and grows. When winter sets in, encased in the cone structure, the larva is protected from predators, but not from the cold.

The larvae aren’t freeze tolerant. Instead, they rely on extreme supercooling, the process of lowering liquid temperatures to below the freezing point without becoming a solid. How do they do this? Overwintering willow gall larvae can contain as much as fifty percent glycerol, historically used in cars as anti-freeze. Some individuals in Alaska were found to have extreme supercooling that allowed them to survive down to -76 degrees Fahrenheit.

At some point in the spring, the larva will pupate and the adult gall-midge will emerge. They don’t have mouthparts to chew their way out of the gall. Instead, they simply push and squeeze between the overlapping leaves of the gall and fly away.

A Redpoll Winter in New England

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Wednesday, January 12th, 2011

Like a gift from Santa Claus, Common Redpoll flocks arrived from the far north at the end of December. Birch, alder and spruce trees across the boreal forest often fail to produce seeds in even-numbered years. Without food to survive the cold winter, redpolls move southward by the tens of thousands. This kind of migration is called an irruption, and we’re in the middle of one here in New England.

During an irruptive migration, flocks of redpolls are usually comprised of fewer than 100 individuals. But occasionally they can balloon to amazing numbers. For example, in March 1941 a birder reported a flock of 3,000 to 4,000 redpolls moving up the Connecticut River valley between Vermont and New Hampshire.

The flock at my feeder has been fluctuating between 30 and 60 individuals for several weeks now and they are eating me out of house and home. Redpolls can store seeds in their diverticula, expandable sections of the esophagus. The diverticula can hold up to 2 grams (about 15% of their body mass) of seeds. Depending on the type of the seeds, this gives them about a quarter of their daily energy needs during the winter cold.

Once they have filled their diverticula, they find a sheltered location to regurgitate, husk and swallow the seeds. Sitting in a sheltered location offers safety from predators, but it also saves significant energy when it is very cold.

It looks like my bird feeders are nearly empty again. Its time for another trip down the snow covered road to the feed store once again!