Genetic evidence provided by researchers at the Max Planck Institute for Ornithology, in collaboration with a colleague at the Cawthron Institute in New Zealand, challenges the prevailing belief that sight and hearing are the primary senses of birds.
The 2008 study suggests that the sense of smell may hold comparable significance for birds, akin to its importance for fish and mammals. This finding contradicts the previous assumption that avian olfaction is relatively underdeveloped.
Did Birds Give Up Their Sense of Smell for Better Sight?
An article in Popular Science says that the prevailing belief suggested that birds sacrificed their sense of smell in favor of superior eyesight. Birds indeed possess exceptional vision, surpassing that of mammals. Their visual acuity, especially in raptors, enables them to spot prey from great heights or in dark conditions.
Furthermore, eyesight plays a crucial role in mate selection, with male birds displaying vibrant plumage to attract females. Most birds have tetrachromatic vision, allowing them to perceive a broader range of colors, including ultraviolet wavelengths. This enhanced visual capability grants advantages in locating food and increasing reproductive success.
The puzzling question remained: why would the evolution of improved eyesight necessitate a trade-off with the sense of smell? Scientists could find no scientific explanations, only unsupported assertions, leading to a quest for understanding.
Avian Olfaction Is Real
Researchers conducted the genetic study in 2008 focusing on olfactory receptor (OR) genes in birds to explore the importance of the sense of smell in avian species, Science Daily reported. Previous behavioral studies indicated that some birds utilize smell for navigation, foraging, and individual recognition.
The researchers compared the OR genes of eight distantly related bird species, in addition to the well-studied chicken, and estimated the total number of OR genes in each species' genome. They discovered significant variations in OR gene numbers, with the brown kiwi possessing six times more OR genes than the blue tit or canary.
Observing the relative sizes of the olfactory bulb in the brain, the researchers noted similar differences between species. They found a correlation between the number of OR genes and the size of the olfactory bulb, suggesting that the number of genes relates to the variety of scents perceivable.
This finding aligns with similar variations observed in mammals. The research implies that ecological niches may have influenced the repertoire sizes of OR genes in birds, as suggested for mammals.
Additionally, the researchers estimated the proportion of functional OR genes. In mammals, reduced reliance on smell is associated with accumulated mutations rendering OR genes non-functional. However, in the bird species studied, the majority of OR genes were functional, indicating the heightened importance of smell in birds.
Furthermore, the study revealed a unique class of OR genes specific to birds, not found in fish, mammals, or reptiles. The function of these bird-specific OR genes remains unknown, offering an intriguing area for future exploration.
Overall, this genetic evidence challenges the previous notion that sight and hearing are the primary senses for birds. The study highlights the significance of the sense of smell in avian species, suggesting its influence on navigation, foraging, and species-specific ecological adaptations.
RELATED ARTICLE: Birds' Hidden Hearing Abilities: Exploring How They Perceive Sound Without External Ears
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