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This answer to my question about light-as-a-weapon came up with an interesting concept:

The Reflecting-Oven-Jay

This is a small African predatory bird with a perfectly smooth set of wings with an area of ~100 cm2, so maybe the size of a pigeon. It hunts in large flocks, around 10,000 birds to a group (there are plenty of real birds that form flocks this size).

Using some basic multiplication, this flock can focus about 130 kW of sunlight. The flock decides to kill and eat an elephant, who has a metabolism of around 3000 Watts and already has to work to keep cool on a warm day (heat sink ears, spraying water on itself, etc). By spreading out and focusing sunlight on the elephant, the birds totally overwhelm the elephant's ability to cool itself, raising its body temperature by about a degree Celsius every 2 minutes (130 kW / 4 tons*specific heat of water), leading to slow heatstroke and death. Divided evenly, there's a lb of meat for every bird in the flock, a huge windfall, sustaining the group though any cloudy days until the next kill.

I thought this was an intriguing idea as it nicely used light as a weapon in a novel and unexpected (and frankly terrifying) way. Imagine having a flock of these things decide you are their next lunch and start the slow cooking process...

The problem though is that while the end result is at least plausible, the evolutionary path is not obvious. How could a bird manage to evolve and become the Reflecting Oven Jay from a relatively normal starting point?

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    $\begingroup$ I wonder if this adaptation would make it easier or harder to fly. Would it heat the air under the bird, thus providing lift, or would the reflection of light cool down the bird, thus cooling down the surrounding air and sucking the bird down? $\endgroup$ – DaaaahWhoosh Apr 23 '15 at 17:34
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    $\begingroup$ Could become the first bird to actively perform barrel rolls for lift. $\endgroup$ – Spacemonkey Apr 23 '15 at 17:48
  • $\begingroup$ @Spacemonkey +1 internets for that $\endgroup$ – thanby - reinstate Monica Apr 23 '15 at 17:54
  • $\begingroup$ How do they continue to reflect light while flapping their wings? Or hunt anytime around noon? Additionally, full wing area reflection for every single bird in the best solar conditions would only provide about 100kW, they'd be lucky to get 10% of that normally. $\endgroup$ – Samuel Apr 23 '15 at 17:58
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    $\begingroup$ They wouldn't have to be flying when they do their solar cooking thing. They could land around their prey, spread their wings and focus the solar energy that way. Kind of like the bird version of a Slaver Sunflower. I just can't imagine the amount of precision flying it would take for 10,000 birds to focus light on a small target while still maintaining lift and not falling out of the sky. $\endgroup$ – AndyD273 Apr 24 '15 at 16:44
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A baby male African jay bird hatches from its egg. In addition to its colorful feathers, one of its tail feathers has a reflective quality. It could be because this family of birds has had a diet with more aluminum in it than normal, and has adapted to it. Regardless of mutation that caused this reflective pigment to appear, some feathers on this new bird do not absorb any light.

Now, this doesn't make the bird live any longer, or get any stonger, in itself. But let me tell you - he is a hit with the ladies. They see the little glimmer coming from the end of this bird, and they all want some tail (pun intended). This little bird has quite an impressive progeny.

Eventually, because of the popularity of the reflective tails, this trait is more likely to be passed on to future generations. And what is more, the reflection itself becomes more and more pronounced.

One day, while hunting, a certain jay learns that he can reflect light off a feather to temporarily stun a very hard to catch, yet singularly tasty little bug. In turn, this jay becomes just a bit stronger, and lives just a bit longer. While teaching his offspring to hunt, he shows them the trick he learned.

This hunting trick soon spreads through the flock. Later, on another hunting expedition, a few birds are practicing the stun trick. They found, however, that when they all focused their feathers on the bug at the same time, they actually killed it, cooking it through. Disappointed (who wants to eat a dead bug?), they try it again on another bug nearby, which in this case, is actually quite larger than the bug they usually stun and eat. A single bird would never be able to do much harm to it, but they found that when they worked together, they were able to stun it and eat it.

This group of cooperating jays soon became the strongest around. As they taught more and more jays, including their offspring, they were able to take down larger and larger prey.

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    $\begingroup$ Started to write an answer thats almost the same as yours, so I defer to this one. Using reflected light as a mate attraction technique as a start, eventually growing to the point it can be weaponized. $\endgroup$ – Twelfth Apr 23 '15 at 17:00
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    $\begingroup$ Same here but I elaborated a lot more the whole evolution of how it came to use it as a weapon so I put it as a separate answer, giving credit for the whole mating part. Pretty neat idea you got there. $\endgroup$ – Spacemonkey Apr 23 '15 at 17:06
  • $\begingroup$ This is a brilliant start to the answer, hats off to you sir! $\endgroup$ – thanby - reinstate Monica Apr 23 '15 at 17:50
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    $\begingroup$ Upvote for the "want some tail" pun. (And a good answer.) $\endgroup$ – BrettFromLA Apr 23 '15 at 19:09
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    $\begingroup$ This tells a story of learning, not evolution. And it assumes that (these) birds actually teach and learn their techniques, which is something not all animals do. $\endgroup$ – Raphael Apr 24 '15 at 16:58
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Like any evolution really, the reflective properties of the features show up faintly in a few specimen, maybe even more than a single race. But our particular race had more advanced 'societal' ties.

Credit to Seth : A baby male African jay bird hatches from its egg. In addition to its colorful feathers, one of its tail feathers has a reflective quality. It could be because this family of birds has had a diet with more aluminum in it than normal, and has adapted to it. Regardless of mutation that caused this reflective pigment to appear, some feathers on this new bird do not absorb any light.

Now, this doesn't make the bird live any longer, or get any stonger, in itself. But let me tell you - he is a hit with the ladies. They see the little glimmer coming from the end of this bird, and they all want some tail (pun intended). This little bird has quite an impressive progeny.

The trait is now more pronounced in the bird population, and the reflective qualities of their features starts changing their feeding habits. For one, they have to be more careful feeding off normal seeds and flora as predators spot them easily by the sunlight they reflect. This however becomes a pro rather than a con as some of the birds discover they can blind predators to quickly escape their grasp. They take the habit of always feeding in groups, certain birds ready to blind predators while others feed. The change from individual feeding to group feeding however has impacts. For one, food becomes harder to come by. This forces them to modify their food source becoming more heavily omnivorous forcing them to feed in places where they are in even more danger of being hunted. Group size increases again. With so many birds now acting as 'blinders' they start sometimes killing smaller persistent predators (through the method described by OP). The now omnivorous bird sees this as a potentially infinite new food source and again they change their feeding behavior.

Final result is the scenario described by the OP where they no longer bait predators but simply are predators.

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    $\begingroup$ Ah I like the way it's weaponized here. Nice! $\endgroup$ – Seth Apr 23 '15 at 17:13
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    $\begingroup$ And this is a brilliant finish to the answer! I like this ending slightly better than Seth's simply because it evolves more out of necessity/survival than simply being a better tool. $\endgroup$ – thanby - reinstate Monica Apr 23 '15 at 17:53
  • $\begingroup$ This thing is basically an SCP at this point o: $\endgroup$ – Feaurie Vladskovitz Apr 24 '15 at 1:19
  • $\begingroup$ Pardon my ignorance.... SCP? $\endgroup$ – Spacemonkey Sep 25 '15 at 21:08
  • $\begingroup$ Special Containment Project - but you will have to do your own googling: I am not taking any responsibility for your brain. $\endgroup$ – Walter A. Aprile Oct 18 '15 at 9:33
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Envision a pigeon-sized scavenging bird that summers in Europe and spends winters in Africa. During migrations, it travels in large flocks, and disperses at either end to look for gross dead things. Also during the migrations, other birds want to snack on them, and so when one jay gets dazzlingly shiny wings it survives the migrations slightly better just by being confusing to look at.

As this mutation spreads in one flock, that flock becomes incredibly frustrating to hunt. Simultaneously, the birds begin to consciously direct their dazzle during migrations and use it to drive off other scavengers when not migrating. It begins to be effective to stay together to scavenge, because being near these flocks is unpleasant at best and increasingly dangerous, at least to eyesight. Eventually the flocks become coordinated, at which point their victims are not merely blinded.

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