Do birds have a good sense of smell?

Jul 16, 2008
The nocturnal Kakapo, one of the nine bird species in the study, probably recognizes fruit according to their aroma. The same applies to the brown kiwi of New Zealand. Credit: Don Merton

The sense of smell might indeed be as important to birds as it is to fish or even mammals. This is the main conclusion of a study by Silke Steiger (Max Planck Institute for Ornithology) and her colleagues. The sense of smell in birds was, until quite recently, thought to be poorly developed. Recent behavioural studies have shown that some bird species use their sense of smell to navigate, forage or even to distinguish individuals.

Silke Steiger and her colleagues chose a genetic approach for their study. Their research focused on the olfactory receptor (OR) genes, which are expressed in sensory neurons within the olfactory epithelium, and constitute the molecular basis of the sense of smell. The total number of OR genes in a genome may reflect how many different scents an animal can detect or distinguish. In birds such genetic studies were previously restricted to the chicken, hitherto the only bird for which the full genomic sequence is known.

In addition to the chicken, the researchers compared the OR genes of eight distantly related bird species. They estimated the total number of OR genes in each species' genome using a statistical technique adapted from ecological studies where it is used to estimate species diversity. They found considerable differences in OR gene number between the nine bird species. The brown kiwi from New Zealand, for example, has about six times more OR genes than the blue tit or canary. "When we looked up the relative sizes of the olfactory bulb in the brain, we also noticed similar big differences between species", said Steiger.

"It is likely that the number of OR genes correlates with the number of different smells that can be perceived. As the olfactory bulb is responsible for processing olfactory information, we were not too surprised to see that the number of genes is linked to the size of the olfactory bulb." Wide variation in numbers of OR genes, and sizes of olfactory bulbs, has also been found amongst mammals. The implication of this finding is that different ecological niches may have shaped the OR gene repertoire sizes in birds, as has been suggested for mammals.

The high number of OR genes in the kiwi could be explained by this bird's unusual ecological niche. Unique among birds, the nostrils of the night-active kiwi are at the tip of the bill. When kiwis probe the forest floor in search of food, they are guided by smell rather than sight. Indeed the snuffling, nocturnal kiwis are sometimes considered to be New Zealand's equivalent of a hedgehog!

Besides the total number of OR genes, the researchers estimated which proportion of these genes are functional. This was done because, in mammals, a reduced dependence on the sense of smell is associated with OR genes gradually accumulating mutations and so becoming non-functional. For example, in humans, which have a poor sense of smell compared with most other mammals, only about 40% of all OR genes may be functional. However, in the bird species studied by Steiger et al., the large majority of the OR genes were functional, again indicating that the sense of smell is much more important in birds than previously thought.

From the analysis of the chicken genome three years ago a new class of OR genes was found. Now Silke Steiger and her colleagues have shown that this class of genes seems to be a shared feature of all birds, while such OR genes are not found in other vertebrates such as fish, mammals or reptiles. The specific function of this class of bird-specific OR genes remains unknown.

Citation: Silke S. Steiger, Andrew E. Fidler, Mihai Valcu & Bart Kempenaers
Avian olfactory receptor gene repertoires: evidence for a well-developed sense of smell in birds?
Proceedings of the Royal Society B, published 16.07.2008, doi:10.1098/rspb.2008.0607

Source: Max-Planck-Gesellschaft

Explore further: New England Aquarium offering penguins 'honeymoon suites'

Related Stories

The vital question: Why is life the way it is?

Apr 01, 2015

The Vital Question: Why is life the way it is? is a new book by Nick Lane that is due out on April 23rd. His question is not one for a static answer but rather one for a series of ever sharper explanations—explanations that a ...

Perfume could be the riskiest gift you'll ever buy

Feb 16, 2015

When it comes to making careful plans to impress that significant other, certain things can seem like musts. Classy restaurant – check. Romantic atmosphere – check. Best suit or little black dress – ...

In the face of stress, flies unite

Dec 30, 2014

Flies exposed to a stress signal when in a group adopt a more effective response than isolated insects, found researchers at UNIL and EPFL. These typically solitary dipterans interact to generate a coherent ...

Genes tell story of birdsong and human speech

Dec 11, 2014

His office is filled with all sorts of bird books, but Duke neuroscientist Erich Jarvis didn't become an expert on the avian family tree because of any particular interest in our feathered friends. Rather, ...

Recommended for you

Telling the time of day by color

Apr 17, 2015

Research by scientists at The University of Manchester has revealed that the colour of light has a major impact on how the brain clock measures time of day and on how the animals' physiology and behavior adjust accordingly. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.