Re: [Phys-L] Thermodynamic Crows

[Brian Whatcott <betwys1@sbcglobal.net>]

 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 <phys-l@mail.phys-l.org> 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

joe

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