'Tis the season for wonderful holiday dinners, packed with all of our favorite foods! We can thank our evolution for the complex sense of taste that allows us to enjoy the many flavors at our dinner tables this holiday season. The approaching winter is not only our best time of year for food, but the best feeding season for wild birds as well. Bird feeding has become a national pastime, allowing us to observe our local birds right in our own backyards. The popularity of bird feeding as a hobby has inspired so many different kinds of bird feeds, all crafted in hopes of drawing the best birds to our yards. Some bird feeds utilize artificial fruit and nut flavorings in hopes of attracting more seed and fruit feeders. But is this really an effective way to bring in more birds? In the summer of 2017, I conducted a series of experiments on the feeding and foraging behavior of passerine songbirds in the New Jersey pines. The first experiment, running through the month of June, focused on the effects of artificial flavoring on the quantity and frequency of birds at the feeder. Two artificially-flavored suet cakes were offered at three backyard feeding stations, alongside a suet cake with no flavoring. Over the course of the experiment, the quantity, feeding frequency, and species diversity of the birds at each feeding station were recorded. In the end, it turned out that the flavor of the suet cakes had no real effect on the amount and type of birds that would feed at those stations. In fact, a higher total number of birds prioritized the unflavored suet cake over those with artificial flavoring. So how could this be? Well, while humans tend to choose their food based on their favorite flavors, the sense of taste is very different for passerine birds. Birds can and do make preferential food choices just like we do, but they have different reasons for choosing certain foods over others. Do Birds Taste?The way birds taste their food is largely species-dependent. Ducks, for example, have over 400 taste buds! They can use this wide range of tastes to identify, accept, and reject the foods that are offered to them, just like people do. Hummingbirds can also discern different nectar types by their tastes; as nectar feeders, they have a heightened ability to identify sweet foods. Passerine birds, however, have a more limited sense of taste, but this is not to say that they cannot taste their foods at all. The taste buds of a passerine bird have evolved to identify chemical differences between their foods, rather than differences in the taste itself. This allows them to reject any food that may be harmful or toxic, as well as to determine foods that may have a higher nutritional or caloric content. Birds can detect acidity in their food and water by recognizing the sour or bitter tastes that identify a high acid content. They can also determine differences between salts in salty foods; many shorebirds can identify chlorides by type and will reject food or water filled with salt they don't want. Most other birds will reject salty food and water entirely.
In a study performed at Cornell by students of the University of Pennsylvania, commercial pheasant food was sprayed with a repellent designed to make the food unpalatable to the birds. Both plain and repellent-drenched food was offered to the birds, while many did reject the repellent-drenched food, others took advantage of the lack of competition and continued to eat it. While most of the pheasants did perceive that something was very wrong with the food, the reasons behind it had very little to do with the taste itself. Other studies performed with artifically-flavored bird foods typically had the same results as the June 2017 experiment: the flavoring had no real effect on whether or not the birds would eat it, and in some cases, the birds outright rejected the flavored food in favor of unflavored options. Since birds can detect the chemistry of their food, it's possible that the artificial flavoring was perceived as an abnormal chemical change. The Thanksgiving Taste ExperimentPasserine birds possess a limited olfactory sense in addition to their limited sense of taste. Most passerines are “nose-blind” to the odors of their environment, and the senses of smell and taste are directly linked. People with disorders of the sense of smell may have a difficult time tasting their food, but how does this connection work? There was no better time to determine the link between smell and taste than on Thanksgiving Day, with such a wide variety of flavorful foods available! At Thanksgiving dinner, six different foods were sampled for an experiment: turkey, stuffing, spinach quiche, macaroni and cheese, baked apples, and sweet potato casserole. Each food was sampled with the nose pinched closed, in order to see how the foods would taste with an impaired sense of smell. The results were very different from what was expected! With the nose pinched closed, only salty tastes remained. Sweet tastes became very bland, and no individual flavors—turkey seasoning, the spinach and pepper in the quiche, or the spicees in the sweet potatoes—could be identified. This shows that our taste receptors are in fact linked to our olfactories, and for those with limited olfactories (such as passerine birds), food is not quite as flavorful. Try to eat with your nose pinched shut, and you may discover what it's really like to “eat like a bird!” Our Sense of Taste is in Our GenesHow come we can taste our flavorful foods, but birds can't? The answer lies in our evolution and DNA. Our bitter, sweet, and savory (“umami”) taste receptors are linked to proteins present in our genetic code, with a single protein for bitter tastes and a double protein for sweet and savory. This sense of taste developed to help our ancestors find calorie and nutrient-dense food during an age when food was scarce (unfortunately, this tends to go against us in an age when food is so widely available). These taste receptors also allowed our answers to reject harmful, toxic, or otherwise unpalatable foods found in the wild. These foods usually carry an extremely sour or bitter taste. T1R1, T1R2, and T1R3 are the genetic components responsible for our sense of taste. With these three components combined, we can enjoy our favorite sweet and savory foods. However, it turns out that passerine birds lack this combination. Other birds, such as hummingbirds, have modified versions of T1R1 or T1R3, but the T1R2 component is generally missing from the avian kingdom. Without T1R2, a bird's feeding experience is a lot like trying to eat with your nose pinched shut. The sense of smell and taste are both very limited. While you're enjoying your upcoming holiday feasts, be very thankful that you're not a bird! Then again, if you were a bird, you wouldn't really need to taste the individual flavors in your food. Evolution has done a fine job of giving humans and avians what they need in order to survive; our ability to savor every flavor of our favorite foods is just an added bonus!
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Star D.M.Star D.M. is an aspiring "mad scientist" looking to know the unknown and see the unseen. She holds a B.A. in marine science with a concentration in wildlife biology, and has a particular interest in ornithology, invertebrates, and cryptozoological research. Her inspirations include Dr. Patricia Tannis and Professor Kokonoe Mercury from the Borderlands and BlazBlue series of videogames. Archives
February 2020
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