[obol] Cascara Tree- Empid

[Dan Gleason]

An interesting discussion. Let me jump in with a couple of thoughts.

I don't know what the chemical substance is in Cascara that causes  
the problems for mammals. I assume that the laxative effect is the  
result of an osmotic imbalance - the chemical is not broken down and  
is too large to be absorbed. This results in an ionic imbalance that  
causes water to leave the surrounding cells and enter the lumen of  
the intestine, resulting in diarrhea. (Much like lactose intolerance  
in humans.) If this is the reaction, then perhaps the birds do not  
have the berries in their system long enough to cause a problem or  
don't eat sufficient quantities. Birds have a much higher metabolic  
rate than do mammals and do not have foods in their systems for long  
periods of time, an adaptation to help keep weight to a minimum.

As for capsaicin, some studies suggest that birds can sense these  
chemicals just as mammals can but that they ignore them. In one  
experiment, Starlings were trained to avoid these chemicals,  
indicating that they are able to detect them just as easily as  
mammals. There is some speculation that capsaicins do not cause a  
"hot" response in birds as they do in mammals, even though they do  
taste them. The ability to sense (but ignore) capsaicins and other  
strong chemicals has also be demonstrated in doves, House Finches and  
Cedar Waxwings and likely holds true for most other species as well.

(Some of us mammals learn to not avoid these chemicals as well. Hot,  
spicy Thai food is certainly something this mammal choses not to avoid.)

A couple of references for birds and capsaicins are:

Norman, Donald M. J. Russell Mason and Larry Clark. 1992. Capsaicin  
effect on consumption of food by Cedar Waxwings and house Fiinches..  
Wilson Bull, 104(3): 551-552.

Mason, J. Russell and Larry Clark. 1995. Capsaicin detection in  
trained European Starlings: the importance of olfaction and  
trigeminal chemoreception. Wilson Bull. 107(1): 169-174.

Interesting stuff.

Dan Gleason
-------------
Dan Gleason
dan-gleason at comcast.net
541 345-0450


On Aug 8, 2007, at 1:15 PM, Arch McCallum wrote:

> So, I can't help but asking, does it have the same effect on birds? I
> would guess not,
> with all those species of birds gobbling up the berries. More likely,
> it has the
> well-known relaxing effect on mammalian digestive systems  
> "intentionally," to
> prevent mammals from eating the berries. Apparently, to continue this
> adaptationist
> line of reasoning, cascara wants its seeds spread by birds, not  
> mammals. Why?
> Perhaps to move them farther away from home than mammals are likely
> to roam, i.e.,
> to increase dispersal distance, e.g., to open areas (see mention of
> "brush line" below).
> This is a hypothesis with a lot of assumptions, e.g., the birds
> swallow the seeds, cascara
> is a laxative for nonhuman mammals in its range, etc. I would love  
> to hear any
> supporting or refuting observations. There's no more fun way to learn.
>
> I do know of one similar situation. I've read (don't remember when or
> where) that capsaicin,
> the hot ingredient in peppers, is not hot to birds, but is to mammals
> in general.
> The hypothesis that goes with that observation
> is that the capsaicin is put in the pepper fruit to deter mammals
> from eating it,
> saving it for the birds, who will wait until the seeds are mature
> when the fruit is red,
> which is a signal visible to birds but not mammals that dinner is  
> served.
>
> Thanks to John Thomas for sharing chittem lore with us.
>
>
> Arch McCallum
> Spinning just-so stories in Eugene
>
>
>
> At 02:00 PM 8/4/2007 -0700, John Thomas wrote:
>> There are some Cascara up and down our "brush line" out here in  
>> farming
>> country. Will have to watch more closely for unusual birds. A  
>> Hermit Warbler
>> or Pacific Flycatcher would be great!
>>
>> When we were kids picking Logan berries for a local farmer, we  
>> played a
>> dirty trick on a town kid by telling him over and over how good those
>> Cascara berries on the tree were. In those days, we country kids  
>> called 'em
>> "Chittem Bark" and knew the tree well as we could peel the bark,  
>> dry it, and
>> sell it to a local hardware store for pickup by some company making
>> laxatives. Being into sustainable pipe dreams (after killing  
>> scores of
>> "Chittem Bark" trees), we even tried leaving a quarter of the  
>> trunk bark up
>> the tree to keep it alive for future harvest. I doubt many made it  
>> but at
>> least our hearts and minds were getting into keeping things alive  
>> and not
>> leveling all to the ground.
>>
>> Back to the town kid: he spent the afternoon in the outhouse after  
>> chewing a
>> handful or two. So ... beware. I imagine one berry would not be  
>> that potent
>> however.
>>
>> John Thomas
>> Silverton
>>
>>
>>
>>
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