Comments on: Argentavis, the largest flying bird, was a master glider

By: common sense

common sense — Mon, 21 Dec 2009 19:12:27 +0000

“could not generate enough lift?” that’s a load of bs. Just use common sense. If the creature cannot generate enough lift, how the hell did it survive? not mention growing to such a size?
Typical scenario:
Bird hungry; bird sees prey and wants to eat… but the landing area is no steeper than 10 degrees. If bird lands, bird cannot get up. Therefore bird dies from starvation.
If such a size is a disadvantage such that it cannot take off at will, then natural selection would favor those that can! Therefore, the stupid scientist’s argument is totally wrong. His argument is as ridiculous as those who claimed that T-Rex was a scavenger.

By: Nathan Myers

Nathan Myers — Sat, 06 Jun 2009 06:46:20 +0000

A paper that confuses basal and active metabolic rates represents a failure of journal review, too. The reviewers should be as embarrassed as the author. This is the first time I’ve seen Ed taken in by a howler.
So, the conclusion is that A. magnificens could produce three times the power needed to take off from level ground, and could therefore climb rapidly too. No doubt it spent most of its time soaring anyhow. Wouldn’t you? (In fact, why don’t you? Lessons are surprisingly inexpensive.)

By: David Marjanović

David Marjanović — Wed, 03 Jun 2009 01:58:25 +0000

It has long been speculated that the constant strong winds of that area were even stronger in the Miocene, and that Argentavis put them to good use, perhaps being incapable of taking off without them and accordingly dying out with them. Good to see that someone tries to throw some numbers at this question.

Aha! I do hope Darren Naish and David Marjanović are reading this.

I have yet to read the paper or the supp. inf., but comment 7 is not encouraging. Confusing basal and active metabolic rate is a major headdesk moment.

By: davem

davem — Mon, 01 Jun 2009 09:32:50 +0000

As a hang glider pilot this doesn’t entirely make sense to me. Hot weather isn’t necessarily good for lift. Post cold-frontal conditions are best for thermals, when the lapse rate is high. When it’s hot, you get temperature inversions that slow climb rates, and may completely stop thermals.
Having said that, modern birds can stay up in thermal lift as long as they like. The bigger the bird, the better they do it. Almost every bird larger than a small songbird will save energy by turning in thermals – seeing birds turn is how I find thermals once in the air. Vultures always land back on a cliff once the thermals start to decay, and wait for the next one to come through.
Albatrosses use dynamic lift (wind shear layers) to maintain height by diving from a high-energy layer to a lower energy layer, then back again, often at wave height. This technique is not available to a land bird.
But you always end up with the landing problem, and the subsequent take off. Shallow slopes don’t work well; if you take off from a shallow hill, you’ll very likely end up at the bottom of said hill, even if the wind is conveniently coming up the slope. What do you do if you have a katabatic wind? Prey is unlikely to be conveniently organizing itself on a steep slope. I fetch the car to get back on top of the hill – these birds are going to have to flap their wings…

By: DDeden

DDeden — Mon, 01 Jun 2009 06:31:48 +0000

To leave this sensible discussion briefly, please note the diagram of the birds getting a free ride up the thermal coilspring escalator, gliding down, and climbing again. Do cumulus clouds float on a coilspring mattress? If so, then at night do they lower?

By: b

Mon, 01 Jun 2009 02:43:33 +0000

HP:
“In my experience with turkey vultures, while they can be magnificent to watch, they’re pretty leery around animals that look like they might scurry.”
american black vultures are of the same family, and are aggressive enough to chase turkey vultures off of carcasses, and predatory enough to take small scurrying critters and newborn livestock. nasty buggers, heh. myself, i can see a hunting cathartid.

By: Mokele

Mokele — Mon, 01 Jun 2009 00:41:22 +0000

Chatterjee’s calculations are wrong.
Look at the supplementary material. He gets the “available power” by taking the basal metabolic rate, multiplying it by the usual 20% for metabolic -> mechanical, and concludes that was the power available, 170W.
How, exactly, is the *basal* rate the power limit? Basal rate is when the animal is *resting*. Many animals have active rates about 10x the basal.
For context: the maximal power muscles can generate, depending on species, is typically between 350-450 W per kg. There are *frogs* that generate more than 170W of absolute power in a jump.
A bird of that size, if even 5% of it’s body mass was flight muscles (a VERY low number), could generate a minimum of 1400 W of power.
That is, hands down, one of the most embarrassing mistakes I’ve ever seen in a paper.

By: amphiox

amphiox — Sun, 31 May 2009 22:17:19 +0000

How do these considerations apply to similarly sized (and even bigger) pterosaurs? Do they apply at all, given the differing anatomy?

By: Darren Naish

Darren Naish — Sun, 31 May 2009 21:03:27 +0000

Hmm, all I will say is: oh look

By: Sven DiMilo

Sven DiMilo — Sun, 31 May 2009 19:10:31 +0000

Chatterjee estimated the maximum amount of power that its flight muscles could have generated. And while substantial, it was still 3.5 times less than the minimum amount of power needed to fly.

Aha! I do hope Darren Naish and David Marjanović are reading this. They have pooh-poohed me several times for making this argument (admittedly, without actual data).