Turns out birds can smell and taste after all

Small songbirds recently made a big contribution to human understanding of the sensory lives of birds. In a Spanish study of blue tits, birds related to our chickadee, researchers painted weasel scent around the entrance to a number of their nest boxes, and then watched to see if the birds showed signs of detecting it.

The birds had been flying in and out to feed their youngsters, but began to hesitate after the scent of their chief predator was added to the entrance. Scientists concluded that the blue tits smelled the weasel musk, feared it was inside the box and had to overcome their fear in order to feed their brood.

If this seems merely intuitive, consider that for a very long time the scientific community has believed that birds, especially songbirds, have little to no sense of smell. Some poorly designed studies in the 1800s and 1900s seemed to prove that olfaction wasn't important to birds.

So the belief grew that with the exception of carrion feeders like vultures, birds rely almost exclusively on their superb vision and hearing to make sense of their world.

And because birds have few taste buds, it was also thought that birds couldn't taste what they eat.

I never quite accepted this assessment — there seemed to be no good reason why birds would lack these two vital senses. Besides, anyone who's seen a Baltimore oriole gobble grape jelly or blue jays relishing peanuts just knows that these birds are tasting a favorite food.

But because researchers persisted in this belief, it led them to ignore what was in front of their very eyes. Increasingly, however, studies are showing that birds share every one of our five senses.

The "no smell" view held sway until the 1960s, when pushback began coming from sometimes surprising sources, such as a scientific illustrator with anatomical training. As she drew the nasal cavities of birds she could see that they had all the structures required for a sense of smell, and she published her findings. This and other reports, among them from studies of homing pigeons, inspired avian researchers to take a new look.

And the conventional wisdom began to be turned on its head. Migrating seabirds were shown to use "odor maps" to guide flight over the trackless ocean. Studies of birds like the New Zealand kiwi showed them smelling their way to food in the dark. Birds also use smell to distinguish unpalatable items from those that are good to eat and to help them avoid predators, like the birds in the Spanish study.

Michigan State University researchers recently showed that during breeding season, dark-eyed juncos were sending odor signals about their potential to succeed as a mate.

Birds can smell but this ability varies widely among bird groups.

The senses of smell and taste are closely linked, and once they began looking more closely, researchers found compelling signs that birds do rely on taste, as well. Birds avoid eating insects they've come to regard as unpalatable (monarch caterpillars, for example), and fruit-eaters can detect when fruit is ripe. Hummingbirds clearly can taste differences in sugar levels found in different plants' flowers.

Birds have many fewer taste buds than humans, but this may not tell much about their ability to taste. Their brains contain an area that interprets taste sensations (and an area dedicated to olfactory cues, as well), which wouldn't be needed if they lacked a sense of taste (or smell). This suggests that they can, indeed, smell and taste, at least to some degree. In most cases, these aren't their primary senses, but they're there.

Why does any of this matter?

Feeling that birds' sensory lives are very different from our own has served to distance us from the avian world. If we could tell ourselves that birds' senses are different from our own, then they seemed more foreign to us, less comprehendible and less deserving of our notice. But the more we find that birds are like us, the more we can empathize with their lives and give credence to their needs.

As Tim Birkhead writes in his wonderful book "Bird Sense: What It's Like to Be a Bird," "We have consistently underestimated what goes on in a bird's head." It's high time we take off the blinders and really see into the world of birds.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.