Crows Ice Fishing for Caddis Larvae: Tuul River, Mongolia

carion crow flock tuul  n mountains n

Corvids – a group which includes crows, ravens, rooks, jays, magpies and nutcrackers – fascinate. On a frigid December afternoon, we found them ice-fishing for caddis larvae in Mongolia’s Tuul River in the heart of Ulaanbaatar. (Click any of the photos for a larger view.)

The most intelligent of all birds, and with a brain-to-body-mass ratio rivaling that of the great apes and cetaceans, crows and their allies often exhibit remarkable behavior. Members of this family have been observed using and to some degree engineering purpose-specific tools – the only nonhuman animal other than the great apes to do so. There’s little doubt that certain feeding behaviors adopted by crows have been learned by watching other birds and animals.

carrion crows wings n cadis n

Note the object in the beak of the crow on the left. It’s a caddis larva casing.

The Tuul River flows through Ulaanbaatar, Mongolia’s capital city. Despite urbanization, the river’s water quality remains high – good enough to support species of trout as well as sensitive aquatic insects such as mayflies, stoneflies and caddisflies – species which spend the early part of their lives as larvae on the bottoms of clean rivers and streams. The Tuul is fast-flowing. Consequently, despite weeks on end of sub-freezing temperatures, here and there pockets of water remain open over shallow, stony, silt-free bottom.


We took a cue from watching the crows and began scanning the ice for caddis larvae casings. As our eyes tuned into the proper size and shape, the empty husks appeared everywhere. This casing, constructed of tiny sticks and pebbles, is about 1.5 inches long (3.8 cm) and belonged to a member of the Northern case maker caddisfly family. 

Perhaps the crows learned of the abundance of wintertime food in these areas of open water by watching dippers – a robin-sized bird that happily plunges into pools and riffles in all seasons in search of aquatic insects and small fish. In fact, on this day we saw a white-throated dipper submerge itself in one of the riffles where the crows were feeding and come up with a small fish.

carion crow w caddis n

Here a carrion crow (Corvus corone) has his prize – a caddis larva pried from its pebble and stick casing.

Not adapted to plunge into water, the crows were fishing from the edge of the ice – thus gaining access to water not overly deep, but deep enough to provide habitat for slow-moving caddis larvae. Resourceful birds, are crows.

7 thoughts on “Crows Ice Fishing for Caddis Larvae: Tuul River, Mongolia

  1. After reading your recipes, when I saw this, I thought of you-bet you will have a twist or two to make it yours. Judy Nation


    9 slices thick cut vegan bacon, diced .
    12 tablespoons butter
    2/3 cup all-purpose flour
    5 cups whole milk
    2 cups heavy cream
    1 cup buttermilk
    5 russet potatoes, baked, peeled and cubed
    1/2 cup scallions
    2 cups vegan ham, diced
    2 cups shredded extra sharp cheddar cheese (do not use already shredded cheese)
    1 cup sour cream
    1 teaspoon kosher salt
    2 teaspoons coarsely ground black pepper (not fine)
    Cook vegan bacon in a large skillet over medium heat until browned. Remove and set aside.
    In a large Dutch oven (7 quart) or large stockpot, melt butter over med-low heat. Whisk in flour until smooth (no lumps). Gradually stir in milk, cream and buttermilk, whisking constantly until fully incorporated and slightly thickened. Add potatoes and scallions. Bring to a boil, stirring frequently, making sure to scrape the bottom.

    Turn heat down to a low simmer, cover and cook for 10 minutes. Add vegan ham, bacon, cheese, sour cream, salt and pepper. Stir until cheese is melted. Serve.

    You can easily add more cheese to the top and place the soup under the broiler for 30 seconds to get that melty cheese look.

    [ As for me, skip the vegan and use the real stuff.]

  2. I love your focus on the environment. Tragically it seems all too few people of the upper US and Northern Asia are as fascinated with God’s creation. Thank you for you continuing efforts to help us cherish our lives.

    • Thanks Joel. We feel lucky to live on the edge of a city where almost in our backyard there are opportunities to walk along a river and through forests. But it’s also fascinating to see examples of adaptation as the city expands.

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