Alpacas and llamas can eat brush and bark and such since they have stomachs like goats and deer.
In case you are interested, here are some differences between llamas and alpacas:
Alpacas are generally smaller than llamas but not always.
Llama ears are tipped over on the ends, often called "banana" ears.
Alpaca ears are more like "spears"
Alpaca ears are generally fuzzier.
Alpacas have fuzz on top of their heads; llamas usually don't.
Alpaca coats are generally finer and very soft; the fibers have "crimp" making them good for spinning. A girl petting a young alpaca said "it's like a cloud!"
Llama coats generally have more straight hairs, often not as soft, no crimp; sometimes mixed with alpaca or sheep for spinning.
Most alpacas have coats of one color.
Llamas can be wildly colored with patches of brown, black, white, tuxedos, spots. The colors and patterns generally don't pass from parent to young. One born here has unusual white leg coloring - mother is all black.
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Llama ears
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Alpaca ears, left and right
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Another difference is harder to see - llamas are generally more intelligent, inquisitive, and "personable". Some people compare alpacas to sheep. Llamas are often used as pack animals. The Leconte Lodge high on top a peak in the Smoky Mountains uses a train of pack llamas to carry all the supplies up and down the mountain. A one-way trip takes them about 4 hours - there is no road.
JKJ