See subject. Another criterion as to general nutritional net gain, would be supply and expenditure to getting to it.
I think this metabolic calculation is a good starting place. But I have no idea how you would get the information on energy spent of chewing through and separating nut from shell.
What’s the point?
In the wild, the best nut is the one that’s available.
So - acorns.
Cashews
No shells (and not really a nut)
Just don’t eat cashews raw… Raw cashews contain a toxin called urushiol which is the same toxin in Poison Ivy… I wonder how people figured out that you could eat cashew if they first made people sick and gave them rashes… Someone just figured out you could cook the poison off?
How about the Sami people of Northern Europe who fed fly agaric to reindeers. They would then collect the reindeer urine and take of the urine to hallucinate… Now how the hell did they know if that would work and why did they try in the first place?
Well, humans have been cooking food for a long time to make it more edible, so finding out that cashews could be cooked to remove a toxin isn’t that much of a stretch. On the other hand, reindeer urine, WTF?
That is my guess as well. They are abundant and they are easy to shell unlike say, black walnuts. Many acorns open on their own as they dry. Native Americans made acorn flour because it is tedious but easy enough to get large quantities and shell them. It has to be easier for a squirrel with those teeth and evil little paws plus they have fairly low daily calorie requirements.
Acorns are well-wounded nutritionally as well. You are looking at an animal-plant feedback loop in nature. Why do you think there are so many oak trees in some places? One reason is the squirrels ‘plant’ the nuts because they are a great food source for them.
Squirrels probably go for the nuts in the state that is easiest to consume. They may get them while they’re immature and softer, or after they fallen and softened up from degradation of the shell. In those cases it’s not so much a particular type of nut as what condition it’s in when eaten.
Animals can also be adept at selecting food for high nutritional value, so there could be cases where greater work still rewards with better nutrition. And that could vary through the life cycle of the fruit as well.
But if this about going to the store to buy nuts in shells to feed squirrels, what difference would it make? Buy a lot of the cheapest nuts, the squirrels won’t care.
In terms of food value vs work in shelling, I reckon pecans are going to be up there - high fat content - thin shell.
Sweet chestnuts would also be a good contender, as long as we’re calculating the effort of shelling them after they naturally fall out of their spiny cases.
Acorns are plentiful (but abundance is not what the OP is asking, I think), but acorns aren’t so rich in fats as many other nuts.
Actually, even the “raw” cashews you find in the stores have been steamed to remove the urushiol oil. Of much more concern is the gaseous hydroxyl acid solution used in this process; the acid in this form has been known to cause severe burns and blisters on contact with exposed skin.
Hydroxyl acid doesn’t sound much worse than what urushiol does to me-
If you knew the time it took a squirrel to get through a nut, and some numbers on basal metabolism you could certainly do a calculation of the calories consumed. Maybe not terribly precise, but close enough.
To do a similar calculation on humans: if you burn about 100 calories an hour (2400 a day is a little on the high side, but close enough). So if it takes you an hour at minimum wage to earn the money for a double cheeseburger with fries, you’ve consumed 1000 calories and burned 100.
My guess is that the math would look similar for squirrels and any nut. Nuts are high in protein and fat; any amount of work to open them is going to be tiny compared to the calories obtained.
Not necessarily. Several different kinds of nuts may be available at the same time, and the best one to eat will be the one that gives the best energy return versus handling time.
Another factor that has to be considered is toxins, as has been mentioned for cashews. Acorns are high in bitter tannins, which is why they generally require leaching to make them suitable for humans to eat.
As a side question, is there anything bad about feeding field corn to squirrells? Will they get proper nutrion? Will they get too fat from not working at shelling nuts? I used to feed the squirrels “wildlife food”, which was corn, peanuts, sunflower seeds, etc. but that got expensive and made a mess on my deck so now I buy 50 lb bags of corn from the local farm goods store.
Another side question: a few weeks ago a squirrel sat on my carport roof, eating a nest of tent caterpillars like it was a stick of cotton candy. Was it nutritional, or was he eliminating a rival?
Nutritional, I’m sure. Squirrels are quite willing to ingest animal protein if it is easy and available - eggs, baby birds and bugs for example. There are even examples of some species hunting smaller rodents on occasion.
When considering what is best for the squirrel, as opposed to strictly considering calorie efficiency, you have to include the fact that their teeth never stop growing – so a certain amount of chewing tough materials is necessary.
The one that is feasting on the suet block outside my window seems to do his needed chewing on the metal parts of the squirrel-proof bird feeders trying to get at the seeds.
ETA: The squirrel and the suet block both live in a walnut tree.
Yes. You’ll get more squirrels. And squirrels are evil. There’s a reason we call them ‘chitterdemons’ and try to shoot as many as we can. I miss the bobcat a few years ago, who greatly reduced our squirrel population, before moving on… <sigh>