Fresh perspective on camouflage for free-ranging chickens

[NorthwoodsChick]

Some of us who free range our chickens look for breeds with good natural camouflage, or even attempt to select for camouflage when breeding. If you're in those categories, you might find this interesting. A flaw with what we consider to be "good" or "bad" camouflage is that we don't see color the same way as chicken predators do. Upon realizing this, I did some research, which culminated on this post that I shared in another thread a while back:

Maybe I'm biased, but I thought this might warrant its own thread, as I haven't seen many people talking about this subject. I'd love to discuss this with anyone who's interested, and I'll probably be sharing some more images that I've run through this program, as I feel it's a really useful visualization.

If anyone wants to test pictures of their own birds, the app is CVSimulator on google play. You could also post them here and I'll run them through for you, if you don't want to download an app

very interesting theory. I’ll download the app and give it a try on my flock. Give me a few days to post back.
Thanks for sharing.

 

[Vulpes vulpes]

It makes sense -- most bird predators are hunting with sight alone -- few birds have a good sense of smell. Most mammal predators hunt using sight along with smell or auditory cues, and the thing that they are using most out of their sight is not so much acuity or patterning but detecting movement. Hence freezing can be a way to throw off a mammal predator.

This is part of the truth, though there's more to it than that. Save for a few exceptions, all mammals are dichromats, even animals that would greatly benefit from better color vision. This is why hunters can wear bright orange without scaring away deer.

The common ancestor of all tetrapods (anything with four limbs; reptiles, mammals, birds, amphibians) was a tetrachromat, seeing four primary colors. Where most birds maintained that ancestral tetrapod condition, scientists hypothesize that mammals went through a "nocturnal bottleneck." Barring marsupials, all extant mammals descend from a nocturnal ancestor. Seeing fewer colors improves night vision, so mammalian ancestors lost two of their cone types many millions of years ago. Funnily enough, it's a lot easier to lose a trait than it is to evolve one, so most mammals have to just make due with two primary colors. However, most being frugivores, there is a lot of selective pressure for primates to not only find fruits, but identify species and ripeness. Because of that, primates have evolved to just barely differentiate between red and green, and are the only mammal I know of to do so.

 

[Vulpes vulpes]

Here's a graphic of our vision vs that of most birds (and presumably that of the ancestral tetrapod):

This, though greatly simplified, shows where the peaks of our color reception are, which corresponds to our different type of cones. It isn't to scale, but it properly conveys what I mentioned in my last post; birds have very evenly dispersed peaks, where ours are more uneven. The fact that our "red" and "green" are so close together shows that they only recently diverged from being the same cone. In most mammals, there is only one peak there instead of two.

Sidenote: because most birds see four primary colors, that means that where we can use a color wheel to represent our vision, birds would need a "color tetrahedron!" Scientists use this visualization somewhat frequently

 

[BlindLemonChicken]

scientists hypothesize that mammals went through a "nocturnal bottleneck."

In what geologic era does this bottleneck occur? I would think that it would have something to do with the dominant reptiles that were running around when mammals evolved but then I would expect them to have started out nocturnal, not to have evolved into that. Perhaps it was driven by climate change instead and moving about in the cooler night temperatures was advantageous.

 

[Vulpes vulpes]

In what geologic era does this bottleneck occur? I would think that it would have something to do with the dominant reptiles that were running around when mammals evolved but then I would expect them to have started out nocturnal, not to have evolved into that. Perhaps it was driven by climate change instead and moving about in the cooler night temperatures was advantageous.

Mammals are the only extant synapsids, a group that was very diverse in the Triassic. After the end Triassic extinction, archosaurs diversified faster and mostly replaced synapsids. Only mammals persisted, since they were small generalists that weren't as affected by the extinction event. From what I understand, mammals were likely nocturnal from the beginning, and mostly stayed that way until the end Cretaceous extinction allowed them to diversify further. Placental mammals and marsupials diverged somewhere in the Jurassic, and marsupials seem to have maintained some of their ancestral color vision (though they might have lost the ability to see UV). So from what I understand, this probably means that mammals had at least trichromacy into the Jurassic period, but had lost it by the Cretaceous

 

[BlindLemonChicken]

From what I understand, mammals were likely nocturnal from the beginning, and mostly stayed that way until the end Cretaceous extinction allowed them to diversify further.

That makes sense. I have a vague understanding of dinosaurs from a geologic perspective but didn’t study mammals at all.

 

[Vulpes vulpes]

That makes sense. I have a vague understanding of dinosaurs from a geologic perspective but didn’t study mammals at all.

I'm not super well versed either. I am a big dinosaur nerd though, and taxonomy fascinates me. Mammals still descended from a diurnal ancestor, it's just that the first animals that we'd refer to as mammals were probably already nocturnal.

 

[Mother of Chaos]

In what geologic era does this bottleneck occur? I would think that it would have something to do with the dominant reptiles that were running around when mammals evolved but then I would expect them to have started out nocturnal, not to have evolved into that. Perhaps it was driven by climate change instead and moving about in the cooler night temperatures was advantageous.

Since many (most?) reptiles are diurnal, depending on the sun for heat, it would make sense that the early small mammals might survive by being nocturnal.

 

[BlindLemonChicken]

Since many (most?) reptiles are diurnal, depending on the sun for heat, it would make sense that the early small mammals might survive by being nocturnal.

I guess I don’t understand how that would be a bottleneck then. If they started out nocturnal then became more diversified it’s more of a nocturnal cone lol. There must be a point where diurnal mammals explode and then the cladogram visually resembles a bottle I suppose.

 

[BlindLemonChicken]

I had to look it up…the extinction of dinosaurs is the explosion of mammalian diversity though mammals were not nocturnal to begin with. Those visual traits evolved along with ectothermia as a means of avoiding cold-blooded reptiles. So it is an actual bottleneck. That’s my curiosity sorted