Above photo courtesy RedButteCanyon.net. Porcupines tend to eat bark for sustenance.
History of The Disappearance of Porcupines:
: Montana Outdoors, “Where Have All The Porcupines Gone?” by Ellen Horowitz: http://fwp.mt.gov/mtoutdoors/HTML/articles/2015/porcupines.htm#.Wc6D1BNSxBw
: The Sacramento Bee, “The killing agency: Wildlife Services’ brutal methods leave a trail of animal death” by Tom Knudson: www.sacbee.com/news/investigations/wildlife-investigation/article2574599.html