The bird species that evolved from carnivorous dinosaurs cannot taste sweetness, only experiencing the savory flavor (umami). However, some bird species, such as hummingbirds and songbirds, defy this trend.
Most Birds Cannot Taste Sweetness
Generally, most mammals can perceive five basic tastes: sweet, sour, bitter, salty, and umami (savory). On the tongues of mammals, including humans, there are four types of taste buds: circumvallate papillae, foliate papillae, fungiform papillae, and filiform papillae. Each type can contain between 5,000 and 10,000 taste buds.
In fact, every part of the tongue can taste all five flavors. As humans age, some taste buds stop regenerating. Therefore, elderly individuals typically have around 5,000 taste buds, which weakens their ability to perceive flavors.
A notable point is that spiciness is not a flavor. Scientists have identified the five official tastes that many mammals can perceive as sweet, sour, bitter, salty, and umami (savory). Meanwhile, spiciness is a pain signal sent to the brain by nerve endings in the tongue, warning of burning sensations or pain.
Hummingbirds can detect sweetness in 1/4 of a second.
Many mammals cannot perceive all five flavors, such as felines and marine mammals. However, most vertebrates can taste sweetness because they possess the TR1 gene family. The T1R1 and T1R3 pair helps animals detect amino acids, the organic compounds that contribute to the savory taste. Meanwhile, the T1R2 and T1R3 pair detects sugars, allowing species to taste sweetness.
However, Maude Baldwin, a researcher at Harvard University, discovered that certain bird species lack the T1R2 gene, which prevents them from tasting sugar. These birds can still perceive amino acids.
By studying the genomes of ten bird species, ranging from chickens to hummingbirds, Baldwin explained that birds cannot perceive sweetness because they evolved from carnivorous dinosaurs. Their diet was rich in protein and amino acids but low in sugars. Gradually, their T1R2 gene disappeared. In modern birds, this gene is entirely absent, preventing them from tasting sweetness.
But There Are Exceptions
Hummingbirds are an exception to the general trend of taste perception among birds. Daily, they consume a quantity of nectar greater than their body weight. This species can detect the difference between water and sugar in just 1/4 of a second. Their tongues can move up to 17 times per second to taste food.
Researchers found that hummingbirds perceive amino acids less effectively than other birds but respond strongly to carbohydrates, which create sweetness. Consequently, the T1R1 and T1R3 gene pair in hummingbirds mutated, enabling them to taste sugar.
To explain this, researchers suggest that in the past, hummingbirds had a genetic makeup similar to other bird species, meaning they could only taste amino acids. However, these birds frequently visited flowers to catch insects and inadvertently encountered the sweetness from nectar or the water collected in flowers. Over time, their genes changed, allowing them to perceive sweetness more distinctly than their relatives.
The research on hummingbirds sparked Maude Baldwin’s interest in the taste perception of these flying animals. Continuing her research into early 2021, Baldwin and a team at the Max Planck Institute discovered that songbirds, comprising over 5,000 species such as larks, cardinals, and thrushes, can perceive sweetness. This ability is not related to their diet.
Initially, scientists systematically studied the diets of various bird species. They found that some lineages of songbirds consume a substantial amount of nectar daily.
This is connected to the ancestors of songbirds living in Australia, an area with natural conditions suitable for flowering plants and fruit trees rich in sugar. Expanding their research, scientists were surprised to discover that many songbird species that do not consume nectar still prefer sweet liquids over plain water.
To determine the origins of this ability, researchers reconstructed the T1R1 and T1R3 genes in the ancestors of songbirds, finding that they could effectively taste umami. Amino acids, which contain protein molecules, contribute to sweetness.
The detection of sweetness in songbirds is more developed and sensitive than in other species. Thus, the ancestors of songbirds had the ability to taste sugar long before they proliferated across the planet. Therefore, whether individuals consume nectar or not, they still have the capability to perceive sweetness.
Interestingly, the differences in songbird species such as canaries and larks coincide with gene mutations observed in hummingbirds. Although their tongue structures differ, they all developed a better ability to taste sweetness compared to umami.
Based on these new findings, scientists suspect that the perception of taste has a profound impact on the evolutionary process and distribution of songbirds. For instance, Australia is home to many songbird species.
This region also contains abundant sources of sugar, such as insect secretions and tree sap. As songbirds migrated from Australia to other continents, they chose to thrive in ecosystems rich in sugary food sources.
From the study of sweetness perception in certain bird species, scientists hope to understand changes in digestion, metabolism, and the evolution of these animals.
