14,400-year-old Bread 

Too Warm or Too Cold to Fly 

Eye Movements and Personality 

Shark Tourism 

Can Lightning Strike You in the Shower? 

Moth Wingtips Confuse Bat Radar 

Elephants Smelling Far Away Food 

Modern Biology in a Monastery Garden 

If a river has a chance, it will meander, winding over the land in a series of loops. Geologists even call these loops "meanders."

You can see meanders on a map--along the lower Mississippi, the Alabama River near Selma, The Arkansas near Tulsa, the Ohio near Evansville, and on thousands of smaller streams--wherever there's a steady flow of water over nearly flat land of fine-textured soils.

Rivers meander because any small bend in a river tends to grow.

Water flowing around a bend in a river is a little like a car speeding around a bend in a road. The water is thrown toward the outside of the turn. That fast-moving water erodes the riverbank on the outside of the bend.

Meanwhile, on the inside of the bend, the water flows more slowly. Sediment held by the water can settle out and accumulate along the inside bank.

So the water eats away the outside of the bend while it builds up the inside of the bend. The bend in the river grows into a big loop.

When the loop gets big enough, the water cuts across the narrowest part of the loop and starts the meandering process all over again. The cut-off loop becomes an oxbow lake.

A meandering river often alters its course. Mark Twain, in his book Life on the Mississippi, says that steamboat pilots of his day traveled up and down the river even when they weren't working, just to keep track of the latest changes in the course of the water.

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Hummingbirds have a voracious appetite for nectar, the sugary fluid secreted by flowers. To survive, they usually drink between five and fourteen times their weight in nectar every day. Finding all that nectar isn’t easy. Some flowers may have already been emptied of nectar by other visitors, or might be occupied by dangerous insects such as ants.

Biologists want to understand how hummingbirds use their senses to find the right flowers to feed at. They have long known that these tiny birds can locate flowers by vision. Although vultures are known to use the sense of smell to detect the corpses of dead animals, smell didn’t seem to play a role in the foraging behavior of hummingbirds. Earlier studies, for example, found no evidence that hummingbirds could use smell to tell whether or not a flower contained nectar.

In 2021 a team of researchers from California published the first evidence that hummingbirds do use smell to avoid danger. The researchers showed that hummingbirds could detect and avoid the smell of a chemical secreted by Argentine ants to attract other ants, and the smell of a defensive chemical released by some other ant species. 

The researchers allowed more than one hundred hummingbirds to choose between two feeders. One contained sugar water alone, and the other contained sugar water scented with one of the ant chemicals. The hummingbirds specifically avoided the chemicals secreted by dangerous ants, but didn’t avoid harmless smells. They ignored the scent of a common food additive not found in nature, and the smell of European honeybees.

The finding helps biologists better understand how animals use their senses during the complex task of foraging for food.

Reviewer: Danielle J. Whittaker, Michigan State University

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