Why do birds flock in winter?

If you live in a temperate climate and pay attention to your local birds, you have probably noticed that their preferences for companionship change with the seasons. In spring, pairs stick close by each other and three’s a crowd—any third-wheel interloper is likely to be chased off in a flurry of angry wingbeats. But in fall and winter, the birds suddenly become community minded, travelling around in flocks of dozens of their fellows. In Chicago in the winter you can find trees liberally decorated with the round orange forms of fluffed-up American Robins, bearing more than a passing resemblance to Christmas tree ornaments. Even in the Bay Area, not generally known for its seasonal variation, huge flocks of quietly chirruping Dark-eyed Juncos make it clear that (mild, occasionally rainy) winter has arrived.

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Not pictured: about fifteen of this robin’s winter friends.

Why flock in winter? Or, why flock only in winter?

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“Rare” birds at the banding station

“Rare” is context-dependent. My Collins Bird Guide lists the Dark-eyed Junco as a “rare vagrant,” but that is, of course, because Collins is a bird guide to Europe. Common birds where you don’t expect to find them are exciting. We have our own rarities at the banding station, birds that may be common in the general region but rarely grace our nets; and although no one else would consider them remotely remarkable, we still get excited.

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Dark-eyed Junco

Juncos flock in huge numbers all around the area, but for whatever reason, they do not like the specific patch of riparian land that the banding station monitors. The banding station catches only around five juncos every year, making them rare by our very particular standards.

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Why it’s important to clean up fishing line

Anza_duckThis handsome bird is a male Ring-necked Duck, but not a happy one. I spotted him splashing in a small lake where a tangle of thin tree branches hung low over the water. A duck having a bath, I thought. Then, as he took a break from splashing and his head drooped so low that his bill went under the surface of the water, Maybe not.

His right foot was caught in a snarl of fishing line and attached to one of the submerged tree branches. The foot was bloody and, from what I could see, the leg broken, probably as a result of his attempts to free himself. There was absolutely no way he could have escaped the fishing line on his own: it was wrapped many times around his foot, the branch, and other branches. It probably caught his foot loosely at first, while he was diving for food; then, as he tugged at it, pulled tighter and tighter, until he was trussed to that branch and pulling against his own flesh when he struggled. Fishing line is made not to snap.

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A predator caught in the act

We were searching for junco nests when I heard the unmistakable tic-tic-tic of junco alarm chipping. We followed the sound a ways and found a pair of juncos perched on a low branch, alarm chipping for all they were worth. Strange of the juncos to be alarm chipping at us when we were so far away, before, I thought. I wouldn’t have thought they’d see us as a threat from that far away. Odd birds. Directly below the branch with the agitated juncos was a small shrub. “The nest will be in there,” I predicted, showing off for my new field assistants.

2015_snake_nest2I parted the prickly branches, and tiny pink beaks gaped hungrily at me. “There they are,” I said, pleased with myself. “Three chicks.”

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And just as I said that, I saw the snake.

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Double rain

Before I studied juncos in California, I studied House Wrens in New York. Most days in the spring and summer I biked from my basement apartment to my field site, which had the no-nonsense label Unit One. The bike ride was an adventure in itself: I prepped for the field season by relearning how to stay on a bike, which I hadn’t done since childhood. (Contrary to the popular saying, it appears I can forget how to ride a bike.) On my way to Unit One I often came upon large snapping turtles stumping deliberately across the road, on the turtle-slow prowl for places to lay their eggs.

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Unit One was primarily a field site for studying Tree Swallows. The front half of it was short grass broken up by regular rectangular ponds, over which the swallows stooped and swirled. House Wren territory lay past the manicured domain of the swallows, in forest dense with brush and mosquitoes. At the start of the field season I feared getting lost in it: the paths were overgrown, and I have a poor natural sense of direction.

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