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Re: [Phys-L] [External] Re: Thermodynamic Crows

And not all crows are black!

On Mon, Aug 10, 2020 at 8:20 AM LaMontagne, Bob via Phys-l <> wrote:

Any explanation that applies to crows probably also applies to most other
birds as well. I can't imagine thermal arguments explaining why a Cardinal
is red, etc.

I think the most likely answer is that a crow is black because it's black.

Bob at PC
From: Phys-l <> on behalf of Brian Whatcott
Sent: Sunday, August 9, 2020 6:37 PM
To: <>
Subject: [External] Re: [Phys-L] Thermodynamic Crows

I see that feather coloration can serve as an honest fitness for mating
indicator in birds. Black bird-feathers are more resistant to bacterial
attack and breakdown than lighter colors. Birds, particularly large birds
operate in a difficult environment: flight, and so there is a conflict
between the need to acquire flight energy, its storage and the cost of air
transport of energy stores, which evolves structures of high strength to
weight - specifically, air-filled hollow bones rather than filled hollow
bones familiar in ground animals ~ and rapid processing of foodstuffs in
favor of excreting significant proportions of energy intake, to reduce its
dwell time. Only the smallest birds can adopt the most expensive flight
mode - hovering. Bill nods to the thermal effects of black coloration,
and this brings to mind an obvious comparison to the black robes adopted by
some itinerant hot desert dwellers. Loose black clothing is found to offer
cooling benefits in Sun & wind (one wonders why it does not find favor
among light-skinned people who are susceptible to UV skin injury but who
opt for light-colored scanty clothing in hot Sunny conditions.) There
are studies which observe a similar thermal benefit to skin temperature in
birds. I am less sure about the suggested need to dissipate heat through
feathers. Feathers & down are desirable heat insulators and I see that a
study finds black feathers are particularly poor at radiating in the UV.
Another study suggests that trapping solar input close to the surface
allows black feathers to shed it in airflow.
Brian W
On Sunday, August 9, 2020, 11:21:45 AM CDT, Joe Bellina via Phys-l <> wrote:

Interesting ideas. However, most bird behavior and appearance has to do
with mating with prompts coming from appearance and behavior. So another
question might be, considering that crows are all black what are the mating
prompts that allow them to take the advantages you have suggested and why
haven’t other birds evolved as the crows have?

stay well


Joseph J. Bellina, Jr. Ph.D.
On Aug 7, 2020, at 7:10 PM, Bill Norwood via Phys-l <> wrote:

Hi Phys-L Thinkers

I am figuring out why crows are all black.

Perhaps if I write something that DOES make sense, it will combine with
the thoughts of others to help explain this black crow phenomenon.

1. Intelligence: Crows are credited with a high level of intelligence:
1a. If a human is hostile to one of them, they will have a meeting where
all crows become informed about this particular human, including how to
identify the human.
1b. If a crow gets killed on a particular farm, that farm will be
avoided in all future migrations.
1c. Crows can recognize individual crows as well as individual human

2. Digestion: Crows are omnivores and are known to eat anything. That
would lead to a great variety in energy expended in digesting a particular
meal. That would in turn lead to a great variety in how much heat is given
off by the digestive system and to a need to efficiently expel heat in the
case of a heavy meal. Black would efficiently and quickly expel the heat.

4. Warming and Cooling: A crow finds himself cold standing in a tree,
then flies out into the sunlight and quickly becomes warmed, because his
black coat is also the most efficient heat absorber. So the crow may have a
survival advantage over other birds and small animals in cold or hot
climates. Said differently, the crow may be occupying a predatory niche.

Ok, it’s your turn - any ideas?

Bill Norwood
Retired from,
U of MD at College Park, Physics Dept
Sep 2018

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