A Question For The Lone Ranger

[The Lone Ranger]

By the way, that is a very real concern. In many reptile species, sex determination is not genetic; sex is determined by the incubation temperature of the egg. (It varies by species; in some, higher temperatures lead to more male offspring, whereas in others, higher temperatures lead to more female offspring.)

Many crocodilian species lay their eggs in depressions and then cover them in rotting vegetation; as the vegetation decays, the heat that it gives off keeps the eggs warm. In some species, the mother carefully monitors the temperature of the nest and will add or remove vegetation to maintain an optimal temperature for egg development and a 50/50 sex ratio in her offspring.



As the Earth's climate has been warming in recent decades, we're beginning to see skewed sex ratios in many reptile species. Some sea turtle populations have female-to-male sex ratios of more than 100 to 1. This is not disastrous for those populations -- yet -- because one healthy male can easily inseminate several females, but if the sex ratio was reversed, that would be disastrous. And yes, there is a very real concern that some reptile species will be driven to extinction by increasingly male-biased sex ratios.

[BrotherMan]

Take a look at this rare bird!

[The Lone Ranger]

Neat! I've seen melanistic and albino birds before, of course, but never before have I seen even a picture of a yellow Cardinal.

[BrotherMan]

Since my friend retired he's had a lot of time to do p much nothing. He's had time to stare out the window to, I don't know, look at the world out there. In the middle of our development is one of those man made ponds. As you might expect, a few times a year it's a big attraction for migrating geese.

About a week back it was one of those super windy extra cold days. My friend was completely perplexed by the dumb birds' behavior. He reasoned well enough that it was way to windy to try and fly, so obviously they were resting and biding their time until they could once again take wing.

Here's what he didn't get: Why were they floating about on the water instead of the land?

My guess was that they're insulated so the freezing water wouldn't affect them the way it would us, but his follow up question got me. What about their little paddle feet? Wouldn't that be uncomfortable for them? (He did note that they weren't just bobbing, they were actively moving about on the surface from time to time.)

What gives? Are water fowl just dumb creatures or what?

[The Lone Ranger]

Most waterfowl have a mechanism by which they can restrict blood flow to the lower legs. Along with that, there are almost no muscles in the lower part of the leg -- they're in the upper leg, safely covered by insulating feathers.

Consequently, most waterfowl can almost completely shut down blood flow to the lower legs without endangering metabolically active tissues. So, despite the large surface area of the webbed feet, they lose very little heat to the cold water.


But it gets better. In mammals such as ourselves, the arteries that carry blood down to the lower legs and feet are separate from the veins that carry blood from the the lower legs and feet back to the body. In waterfowl, that's not the case.

In most waterfowl, the arteries carrying blood down to the lower leg and foot are entangled with the veins carrying blood back. This sets up a countercurrent heat exchange. The cool blood flowing back up from the feet in the veins is warmed by the warm blood flowing down in the arteries. This means that by the time the arterial blood flows down into the part of the leg that isn't insulated by feathers, it has given up much of its heat to the venous blood.

Since the arterial blood flowing into the lower leg and foot has been cooled by the time it reaches the feet, the temperature differential between the blood in the feet and the surrounding water is not too great -- therefore, there's a much slower rate of heat loss to the surrounding water than would be the case if the feet were full of hot blood.



So, long story short: between the fact that blood flow is restricted to those tissues in the first place (possible because there's not very much metabolically active tissue present), and the fact that the countercurrent exchange mechanism in the upper leg means that the arterial blood reaching the lower leg and feet is relatively cool -- ducks, geese, gulls, and other waterfowl can stand or float in cold water while losing almost no body heat to the water.

Many mammals have similar mechanisms to reduce heat loss from the extremities in cold temperatures. That is, many mammals (reindeer, for example) can greatly reduce blood flow to the lower legs and feet during cold temperatures, and many have countercurrent heat exchange mechanisms in the legs, so that the arterial blood flowing to the lower legs and feet gives up much of its heat to rising venous blood.

[JoeP]

Diagrams

This is the best thread at .

[Ari]

So how should I try to talk with ravens?

the local cliffs where I've been venturing often have heavy updrafts enough so that there's a hangglider launching area and the birds come to play and coast on the wind, often floating in one spot and playing with each other. It's also an off leash dog walking area. The ravens there are clearly adapted to the area, expecting you to move when walking down a path and waiting their turn to drink from the dog height water fountain.

I've been considering trying to befriend some of them or at least chat/interact with them, and am trying to figure out the best way to go about doing this. Obviously the easiest is food and also the most suggested against. While I'll probably use food as a bonder but it's not sustainable (In the case of many mammals giving a critter some of the food you're eating will either get you mugged for the rest of it, or treated more friendly even if you never give them anymore food). Which leads to the issue that I just haven't had that many interactions with birds and don't understand their world like I do many fuzzy mammal critters.

Birder friends have recommended two books that I need to hunt down at the library, Mind of the Raven and Bird Brain but haven't yet.

Any suggestions of ways to interact?

[The Lone Ranger]

Yeah, my first thought upon the idea of trying to "befriend" any wild birds is -- don't.

They're only going to "befriend" you if you have something to offer them. As they're wild ravens, they don't want you to pet them or otherwise pay attention to them -- really, the only thing you can provide that they might want is food.

And, as you've noted, feeding them is a bad idea, for several reasons. First, any ravens who learn that humans are reliable sources of food and get into the habit of approaching humans for food are sooner or later going to get injured or killed by someone. Besides, corvids are notoriously aggressive birds, and any who learn that they can approach humans for food are likely to quickly graduate from begging for food to demanding food. (It's not unknown for wild ravens who have learned that humans are a food source to "punish" people who don't cough up the goods on demand.)



Probably the best choice is to hang out where they do, and let them get used to your presence. Maybe set up a comfortable lawn chair and do some reading for an hour or two a day. There's good evidence that ravens can learn to recognize individual humans, and if they figure out that this particular human is always around and never tries to hurt them, they'll at least be inclined to tolerate your presence.

From there, it wouldn't hurt to try mimicking some of their vocalizations. They're curious birds, and might be inclined to approach in order to try and figure out what you're up to.


Honestly, the best you can probably hope for from wild ravens is that they'll learn to tolerate your presence; trying to befriend them is likely a bad idea for both them and for the local humans. But getting them to the point that they'll tolerate your presence would be rewarding in itself, as you could then watch them from close-up.


And yeah, Bernd Heinrich is probably the world's leading authority on ravens. I've read quite a few of his books, and they've all been both informative and very well-written.

[fragment]

How do web-spinning spiders avoid sticking to their own webs?

[Ari]

Indeed, if these were random birds I would be more cautious but they interact with humans and dogs enough and don't mess with them and are clearly there to play.

They hang out with the hanggliders on the same updrafts, and will dodge in and out of winds sometimes floating a few feet above dunes.


I have the benefit of looking distinctive and was considering doing something like wearing a specific home made hat when interacting with them.

[Ari]

Originally Posted by fragment

How do web-spinning spiders avoid sticking to their own webs?

Oow this I can answer!
Two ways. One, not all their web is sticky. They have the ability to produce different types of webbing. In the case of orb weavers, that make these webs , it's the spiral part that's sticky, the radial spokes aren't and these are the ones the spider runs down to catch their prey. When building their web they make a loose spiral of unsticky web and then walk along that as they add the sticky web to the radial spokes.

Spider spinnerets are quite amazing a spider normally has 6 to 8 arranged in a circle that often work in opposite pairs to come together and produce the web. Each set produces different types of long chain molecules which intertwine around each other to allow a variety of web types, some are sturdy and load baring, others are extremely stretchy and others sticky, the spider can adjust them for the webbing they want.
Spinneret SEM close up, (If the gif was slower, you could see how the spider pulls the elastic radial web to attach the sticky webbing while this barely moves the outside structure webbing in comparison).


Two, their legs have many tiny hairs that catch the webbing so when they do need to walk on the sticky webbing they are applying the least amount of surface area against it. They also normally drop a drag line from the center or upper corner when venturing out so if anything goes wrong they can grab it and climb back up to a safe spot.

[ceptimus]

Take up hang gliding! It's fun even without ravens.

[Ari]

Originally Posted by ceptimus

Take up hang gliding! It's fun even without ravens.

Apparently I need some sort of rating and helmet sticker to take off from the cliffs, I can't just jump off, that's frowned upon.
http://www.flyfunston.org/
(With bonus sunset webcam... I see there are a few hanggliders there now).
I will eventually harass the hangglider club but haven't gotten around to it yet.

[The Lone Ranger]

Originally Posted by Ari

I have the benefit of looking distinctive and was considering doing something like wearing a specific home made hat when interacting with them.

That's a good idea. If you're distinctive-looking, it'll be easier for them to learn to recognize you and to figure out that you aren't a threat.

[ceptimus]

I was once circling my hang glider in a thermal and a buzzard was circling in the same thermal but in the opposite direction. It started off lower than me, but gained height faster till it was approaching for a head-to-head impact. It briefly folded its wings and dropped twenty feet or so to pass beneath me, but by the time we had both completed another half circle it was back up to my head height - it was clearly a more efficient flying machine or a better pilot than my glider and me. It repeated its "close wings and drop" stunt for another two or three circles before giving me a withering look, as if to say, "this idiot doesn't know the correct direction to circle in this thermal." It then glided away to find another thermal about half a mile away where it proceeded to out-climb me once again until I lost sight of it.

My experience is that birds that are quite wary and timid of humans on the ground are much more confident and inquisitive when they encounter us in the air. I suppose they rightly feel safe and confident in their aerial skill and ability to easily outmaneuver our lumbering flying machines.

[The Lone Ranger]

For what it's worth, the word "buzzard" typically means different things to Europeans and North Americans.


In Europe, "buzzard" typically means "diurnal raptors, especially large soaring raptors in the genus Buteo."

The Common Buzzard (Buteo buteo) is common in most of Europe and parts of Asia.

In North America, especially the U.S., "buzzard" usually means "vulture" -- especially either the Turkey Vulture (Cathartes aura) or the Black Vulture (Coragyps atratus).

American "buzzards" -- a Turkey Vulture (on the left) and a Black Vulture.

[Vivisectus]

I remember when "Buizerds" were fairly rare in the Netherlands, as we nearly wiped them out along with most of our larger raptors, by using shitty pesticides. I was so excited when I discovered a nesting pair in a small nature reserve when I was a wee nipper.

These days you can see several dozens just by driving down a highway, and when I go "hey look a buzzard!" people give me funny looks as if I am excitedly pointing out a sparrow or something.

[ceptimus]

Yes the buzzard I was talking about was the raptor, not vulture kind. As far as I know we don't really have any specialist carcass only scavenger birds here.

We do have Red Kites, which have also flown near my hang glider.



The Red Kite is more of a scavenger than the Buzzard and does eat carcasses- I've seen them feeding on dead sheep - but it also catches and eats mice, young rabbits and such, along with frogs and worms. It's a very pretty bird, in my opinion, though it was despised and hunted to near extinction in the past.

[Pan Narrans]

Originally Posted by ceptimus

"this idiot doesn't know the correct direction to circle in this thermal."

[thedoc]

Originally Posted by The Lone Ranger

Most waterfowl have a mechanism by which they can restrict blood flow to the lower legs. Along with that, there are almost no muscles in the lower part of the leg -- they're in the upper leg, safely covered by insulating feathers.

Consequently, most waterfowl can almost completely shut down blood flow to the lower legs without endangering metabolically active tissues. So, despite the large surface area of the webbed feet, they lose very little heat to the cold water.


But it gets better. In mammals such as ourselves, the arteries that carry blood down to the lower legs and feet are separate from the veins that carry blood from the the lower legs and feet back to the body. In waterfowl, that's not the case.

In most waterfowl, the arteries carrying blood down to the lower leg and foot are entangled with the veins carrying blood back. This sets up a countercurrent heat exchange. The cool blood flowing back up from the feet in the veins is warmed by the warm blood flowing down in the arteries. This means that by the time the arterial blood flows down into the part of the leg that isn't insulated by feathers, it has given up much of its heat to the venous blood.

Since the arterial blood flowing into the lower leg and foot has been cooled by the time it reaches the feet, the temperature differential between the blood in the feet and the surrounding water is not too great -- therefore, there's a much slower rate of heat loss to the surrounding water than would be the case if the feet were full of hot blood.



So, long story short: between the fact that blood flow is restricted to those tissues in the first place (possible because there's not very much metabolically active tissue present), and the fact that the countercurrent exchange mechanism in the upper leg means that the arterial blood reaching the lower leg and feet is relatively cool -- ducks, geese, gulls, and other waterfowl can stand or float in cold water while losing almost no body heat to the water.

Many mammals have similar mechanisms to reduce heat loss from the extremities in cold temperatures. That is, many mammals (reindeer, for example) can greatly reduce blood flow to the lower legs and feet during cold temperatures, and many have countercurrent heat exchange mechanisms in the legs, so that the arterial blood flowing to the lower legs and feet gives up much of its heat to rising venous blood.

Are there other animals that use this strategy to conserve heat in cold weather, and in warm weather is there some mechanism where the animal can reduce or shut off the effect? I'm thinking primarily about mammal predators like wolves and big cats, and do the hoofed prey animals have a similar mechanism?

[The Lone Ranger]

Many mammals have similar countercurrent exchanges that allow them to greatly reduce heat loss from the extremities during cold weather. Some carnivores do it, for example, and caribou have a particularly well-developed countercurrent mechanism that greatly reduces heat loss from the legs.

Indeed, a series of closely-associated arteries and veins that allow countercurrent exchange of heat, ions, or gases is very common in birds and in mammals; such a complex is known as a rete mirabile (from the Latin for "wonderful net"). Similar arrangements in the gills and swim bladders of many fishes allow for very efficient exchange of O2 and CO2 between the blood and the surrounding water.


Retia mirabilia in the kidneys of mammals allow mammals to produce hypertonic urine, and so conserve water that would otherwise be lost in expulsion of toxic urea.


Capillaries are frequently arranged into capillary beds, and blood flow to capillary beds can be regulated by reducing blood flow to those capillary beds or even bypassing them entirely. So a rete mirabile that is used to reduce heat loss in cold weather can be shut down when it isn't needed.

Depending on how the vessels are arranged, such a system can work to retain heat, or to shed excess heat. For example, many terrestrial mammals (notably many antelopes, for example) have a rete mirabile system in the tissues of the muzzle that helps them shed excess body heat as they breathe. Basically, cool air is inhaled, and heated air is exhaled. This arrangement is particularly important in cooling the blood flowing to the brain via the carotid arteries, and so helps prevent overheating of the brain during high temperatures and/or prolonged exertion.

[thedoc]

Originally Posted by The Lone Ranger

Many mammals have similar countercurrent exchanges that allow them to greatly reduce heat loss from the extremities during cold weather. Some carnivores do it, for example, and caribou have a particularly well-developed countercurrent mechanism that greatly reduces heat loss from the legs.

Indeed, a series of closely-associated arteries and veins that allow countercurrent exchange of heat, ions, or gases is very common in birds and in mammals; such a complex is known as a rete mirabile (from the Latin for "wonderful net"). Similar arrangements in the gills and swim bladders of many fishes allow for very efficient exchange of O2 and CO2 between the blood and the surrounding water.


Retia mirabilia in the kidneys of mammals allow mammals to produce hypertonic urine, and so conserve water that would otherwise be lost in expulsion of toxic urea.


Capillaries are frequently arranged into capillary beds, and blood flow to capillary beds can be regulated by reducing blood flow to those capillary beds or even bypassing them entirely. So a rete mirabile that is used to reduce heat loss in cold weather can be shut down when it isn't needed.

Depending on how the vessels are arranged, such a system can work to retain heat, or to shed excess heat. For example, many terrestrial mammals (notably many antelopes, for example) have a rete mirabile system in the tissues of the muzzle that helps them shed excess body heat as they breathe. Basically, cool air is inhaled, and heated air is exhaled. This arrangement is particularly important in cooling the blood flowing to the brain via the carotid arteries, and so helps prevent overheating of the brain during high temperatures and/or prolonged exertion.

Then I will assume that humans do not have that adaptation because humans evolved in a warm climate and the biggest problem was dissipation of excess heat. Humans had little to no exposure to colder climates and when they did clothing was used to protect from the cold.

[The Lone Ranger]

Most mammals, including humans, use the tissues covering the turbinate bones in the nasal cavities to warm and moisten air as it flows into the nasal cavities. This is one of the reasons why mammals (and birds, which have similar mechanisms -- as did some of the non-avian dinosaurs) can survive so much better in colder environments than can most other animals. If this mechanism didn't exist, breathing in very cold air could potentially damage the respiratory tract. As the air flows out again through the nasal cavities, these tissues reabsorb much of the heat and moisture, so we don't lose so much heat and moisture through breathing as would otherwise be the case.


Of course, in the case of humans, this is a "preadaptation." It's not that we're specifically adapted to living in cold environments, but the structure of the mammalian respiratory system means that we can breathe very cold air without risking damage to our respiratory tracts.

In terms of our anatomy and physiology though, we humans are clearly adapted for warm climates. The structure of the respiratory system just happens to give us the added bonus of being able to breathe cold air, allowing us to survive in cold environments -- so long as we can figure out how to sufficiently insulate ourselves against heat loss.

[JoeP]

Originally Posted by The Lone Ranger

This is one of the reasons why mammals (and birds, which have similar mechanisms -- as did some of the non-avian dinosaurs) can survive so much better in colder environments than can most other mammals.

I'm thinking one of these words was supposed to be another. 'Animals'?

[thedoc]

Originally Posted by The Lone Ranger

Most mammals, including humans, use the tissues covering the turbinate bones in the nasal cavities to warm and moisten air as it flows into the nasal cavities. This is one of the reasons why mammals (and birds, which have similar mechanisms -- as did some of the non-avian dinosaurs) can survive so much better in colder environments than can most other mammals. If this mechanism didn't exist, breathing in very cold air could potentially damage the respiratory tract. As the air flows out again through the nasal cavities, these tissues reabsorb much of the heat and moisture, so we don't lose so much heat and moisture through breathing as would otherwise be the case.


Of course, in the case of humans, this is a "preadaptation." It's not that we're specifically adapted to living in cold environments, but the structure of the mammalian respiratory system means that we can breathe very cold air without risking damage to our respiratory tracts.

In terms of our anatomy and physiology though, we humans are clearly adapted for warm climates. The structure of the respiratory system just happens to give us the added bonus of being able to breathe cold air, allowing us to survive in cold environments -- so long as we can figure out how to sufficiently insulate ourselves against heat loss.

So the genetic adaption was in place, inherited form the mammals humans evolved from and were genetically "switched on" when humans started living in colder climates, like their predecessors.