That's a promising field report on Ursack's durability with small, sharp teeth & birds. However, my comments come from Ursack's web site, under the FAQ:
"Is Ursack resistant to rodents, marmots, wolves, etc?
Ursack is highly effective against Marmots and raccoons. It should not be considered wolf or dog resistant. That's because they have sharp teeth and strong jaws. Bears have great strength, but their teeth are not sharp.
Other rodents have varying degrees of success. Sometimes mice can chew very small holes, but very little of your food is likely to be taken. Some species of squirrels and (we have heard) pine martens have greater success, and may on rare occasion chew holes in Ursack."
This is why I started wondering if the thinner steel mesh of the Ratsack would be a more effective deterrent than the thicker but somewhat chewable Ursack if you hike in areas were rodents are more of a problem than bears. I've also noted that the smallest Ratsack is not only lighter but significantly larger than the Ursack.
I love my Ursack, but I haven't had a rodent try to eat through one yet, so I don't know what to expect. I suppose in bear country, the Ursack is the smart choice since it will protect against large and small animals. But I can't help but think about the big warning sign at the beginning of one of my favorite hikes in the Southern Sierras (Cannel Meadow trail): "WARNING: PLAGUE HAS BEEN DETECTED IN RODENTS IN THIS AREA." Makes me wonder if, at least in this area, a totally rodent-proof bag is better than a bear-proof one.
Oh, and a hanging an Ursack is no problem for a squirrel to get to, so I don't see that as a fool-proof solution, either. I have, however, considered ways of hanging my Caldera Cone above my Ursack, like a wide-brim hat, to keep the small animals away (like the squirrel deterrents for bird feeders), but I haven't managed anything that gives me confidence.