new research debunks trad views on nutrition

[RoyalChick]

That means I have to remember...

I'll remind you.

And if you believe that, I have a bridge to sell you!

 

[Perris]

OK. The avian sense of taste. The following culled from Tim Birkhead Bird Sense 2012 chapter 4 (which is devoted to this sense).

The many and major differences between our own mouths and a bird's beak make it hard to get our heads around what eating is like for birds, and because we humans make a general assumption that all other species live in our sensory world, historically it has been assumed they have little if any sense of taste. But a sense of taste is essential for discriminating between edible and inedible/ toxic food items, so it is intrinsically improbable that birds could function without one.

Anatomically, a chicken has about 300 recognised taste buds, a mallard duck 400, Japanese quail just 60, in the mouth. In most species these taste buds are located at the base of the tongue, in the palette and towards the back of the throat, most of them near salivary glands since saliva (or moisture at least) is crucial for the perception of taste. These numbers seem small in comparison with e.g. hamster (723), rats (1,265), humans (10,000) or a particular catfish (100,000). But the mere number of taste buds is not a reliable guide to what animals can actually taste or how well they can discriminate between tastes.

Birds respond to salt, sour, bitter and sweet tastes as we do; it was not yet known when this book was written whether or not they register the most recently discovered taste, umami. Anyone with an update there please don't hesitate to chip in. Some species have appropriate refinements, e.g. hummingbirds can differentiate levels of sugar in nectar, and wading birds can taste the presence of worms in wet sand. Birds do not seem to be able to taste capsaicin, which is why they can eat chillies with impunity.

Astonishingly, there are (were in 2012) five known species of bird that are toxic, acquiring their toxin by eating something toxic, e.g. a particular beetle whose toxin is more toxic than strychnine. This is a defence against being preyed upon and against feather-eating lice (the toxin is accumulated in the feathers, not the flesh); rubbing off onto eggs in the nest, it may possibly also help to make their eggs unpalatable to snakes. Carolina parakeets may be toxic thanks to eating cocklebur seeds.

Birds do have a sense of taste; it has been under-researched but it is there. There is a lot of work to be done in the area, so if you want to contribute, there are opportunities here.

End of chapter highlights.

So it appears that whoever wrote the fb 'article' is doing that - getting stuck in to research on the avian sense of taste, which is good; some more observation of free-living birds is probably what's most needed now, rather than more book-work or dissections.

There are some areas of agreement and some of disagreement. The sources used by the fb author are less academic / detailed / fact-checked / peer-reviewed than those used by Birkhead, so it's hard or impossible to discover the evidence for the view in the fb piece, and in those circumstances I favour the one whose work I can check and independently validate or dispute. Notably, both have little to say about 'taste buds' in other parts of the body; this is a recent discovery in human anatomy, and it's barely registered for other species. There are taste buds scattered through the GIT and even in unexpected places like the testes. Nor did either talk about birds' ability to taste calcium, which I'm sure has been established now.

 

[Perris]

An interesting postscript, this time from a 1991 Encyclopaedia of ornithology which has just a page on taste, but includes (Brooke and Birkhead edd.; G Martin wrote this bit) "The sense of taste, which is in fact the analysis of chemical composition, is no less sophisticated than the other senses... the Herring Gull and the chicken seem to be indifferent to substances which to humans taste extremely bitter... Carrion and insect-eating birds [that would include chickens I contend] probably depend heavily on taste to determine the palatability of their food, which can often be extremely toxic due to putrefaction or poisons contained within the insect's body as defence. The carrion crow has a great abundance of taste receptors in its mouth and is very sensitive to sour substances. Blue Jays are known to be extremely sensitive to the sour taste of plant-derived toxins (e.g. cardiac glycosides, similar to digitalis) stored in the bodies of butterflies and caterpillars."

 

[Sally PB]

@Perris, this is all fascinating. Thank you.

 

[RoyalChick]

An interesting postscript, this time from a 1991 Encyclopaedia of ornithology which has just a page on taste, but includes (Brooke and Birkhead edd.; G Martin wrote this bit) "The sense of taste, which is in fact the analysis of chemical composition, is no less sophisticated than the other senses... the Herring Gull and the chicken seem to be indifferent to substances which to humans taste extremely bitter... Carrion and insect-eating birds [that would include chickens I contend] probably depend heavily on taste to determine the palatability of their food, which can often be extremely toxic due to putrefaction or poisons contained within the insect's body as defence. The carrion crow has a great abundance of taste receptors in its mouth and is very sensitive to sour substances. Blue Jays are known to be extremely sensitive to the sour taste of plant-derived toxins (e.g. cardiac glycosides, similar to digitalis) stored in the bodies of butterflies and caterpillars."

Very interesting. As I posted earlier I am convinced based on observation of my chickens that they can detect both calcium and protein. Whether that is taste or some other sense I have no idea.
Smell is closely associated with taste. In humans when you lose the ability to smell you also lose some ability to taste (think how stuff tastes when you have a stuffy nose). Did any of the sources talk about smell?
I read somewhere that carrion feeders like vultures have a highly developed ability to smell decay - often from miles away.
I wondered if my chickens can smell protein because they do not seem to sample the food options before homing in on the highest protein.

 

[Perris]

protein. Whether that is taste

I think umami is being associated thus; it's otherwise glossed as the 'savoury' taste.

Did any of the sources talk about smell?

oh yes. Birkhead has a chapter on smell, the Encyclopaedia just 3 paragraphs (but the latter also addresses the avian sensing of magnetism, air pressure, and temperature, via at least 9 different types of receptor cells, so I'll not fault them for that ), and Ackerman's Bird Way 2020 has a lot about it scattered about its pages. I'll collect it together in another post.

 

[RoyalChick]

I think umami is being associated thus; it's otherwise glossed as the 'savoury' taste.

oh yes. Birkhead has a chapter on smell, the Encyclopaedia just 3 paragraphs (but the latter also addresses the avian sensing of magnetism, air pressure, and temperature, via at least 9 different types of receptor cells, so I'll not fault them for that ), and Ackerman's Bird Way 2020 has a lot about it scattered about its pages. I'll collect it together in another post.

Very interesting. I forgot about things like magnetism and air pressure.

 

[Perris]

before I switch to smell, I think a summary of a bit of Raubenheimer and Simpson, Eat like the animals 2020 would be a good idea. Chapter 4 Dance of the appetites:

How do living things know, innately, what they ought to eat? ...the flavour profile of a food indicates its chemical contents - its nutrients. Given that different nutrients have different functions, nature has equipped us with the ability to tell the difference and detect their presence in food. We take it for granted with the macronutrients. Carbs are sweet, protein is umami and fats are rich.

Taste receptors in our intestines keep track of nutrients as they are broken down during digestion, and after they enter the bloodstream via receptors in e.g. the liver and brain.

We can also detect two micronutrients - salt, and calcium (I'm looking at you RC!). We do not have or need specific appetites for the dozens of other nutrients we need. It seems 5 is enough. They drive us to eat protein, carbs, fats, sodium and calcium - the 3 macronutrients, and 2 critically important micronutrients. They have been singled out by evolution perhaps for 3 reasons: 1. they are needed in the diet in very specific quantities - not too much, and not too little. 2. The concentrations of these nutrients varies widely in what we eat. 3. Also, salt and calcium are so rare in our ancestral environments that we needed dedicated biological machinery to seek them out. So Gorillas eat tree bark to get enough salt. Giant pandas migrate long distances to get enough calcium to breed.

Why don't we have appetites for the other essential nutrients like vitamins and other minerals? Possibly because our natural diets are rich in these nutrients, and by eating the right amounts of the big 5, we automatically get enough of the rest. So extra appetites would be redundant and wasteful.

 

[saysfaa]

...so extra appetites would be redundant and wasteful.

Maybe counterproductive too - actively making it harder to get the right amounts of carbs, protein, fat, salt, and calcium.

On the other hand, I've seen evidence that there is some mechanism to cause an appetite for other micronutrients and some sort of response to eatings things that satisfy that appetite. At what point the mechanism is called taste, might be debatable.

 

[RoyalChick]

before I switch to smell, I think a summary of a bit of Raubenheimer and Simpson, Eat like the animals 2020 would be a good idea. Chapter 4 Dance of the appetites:

How do living things know, innately, what they ought to eat? ...the flavour profile of a food indicates its chemical contents - its nutrients. Given that different nutrients have different functions, nature has equipped us with the ability to tell the difference and detect their presence in food. We take it for granted with the macronutrients. Carbs are sweet, protein is umami and fats are rich.

Taste receptors in our intestines keep track of nutrients as they are broken down during digestion, and after they enter the bloodstream via receptors in e.g. the liver and brain.

We can also detect two micronutrients - salt, and calcium (I'm looking at you RC!). We do not have or need specific appetites for the dozens of other nutrients we need. It seems 5 is enough. They drive us to eat protein, carbs, fats, sodium and calcium - the 3 macronutrients, and 2 critically important micronutrients. They have been singled out by evolution perhaps for 3 reasons: 1. they are needed in the diet in very specific quantities - not too much, and not too little. 2. The concentrations of these nutrients varies widely in what we eat. 3. Also, salt and calcium are so rare in our ancestral environments that we needed dedicated biological machinery to seek them out. So Gorillas eat tree bark to get enough salt. Giant pandas migrate long distances to get enough calcium to breed.

Why don't we have appetites for the other essential nutrients like vitamins and other minerals? Possibly because our natural diets are rich in these nutrients, and by eating the right amounts of the big 5, we automatically get enough of the rest. So extra appetites would be redundant and wasteful.

Wow. Calcium. I knew it!