"The kinds of issues we've worked on involve everything from using leg hold traps to catch predators, to the shooting of bison both inside and outside Yellowstone Park," he explains.
Glitzenstein's biggest legal victory came last week, when the Pennsylvania Supreme Court declared an annual pigeon shoot inhumane -- and therefore in violation of the law. The organizers canceled the 65-year-old event.
He's one of a handful of lawyers across the U.S. who are creating new animal protections.
"Animals are incapable of defending their own interests, they're relying solely on us," argues the Animal Legal Defense Fund's Valerie Stanley. "In that respect they're like children, and our legal system recognizes that children have rights and interests and it protects them and gives them guardians. Eventually, we would like to see that happening for animals."
Biomedical researcher Dr. John Gordon feels differently. He says, "I think this entire notion of giving animals rights that one would normally associate with humans reflects a great ignorance about the way animals live and behave."
Gordon worries that victories by animal rights attorneys could threaten research into cures for human diseases. "We cannot move forward in many very important scientific areas without having the opportunity to test ideas and compounds in animals," he says.
And in fact, animal rights attorneys acknowledge they are already planning for law suits to block scientists from using animals in lab tests.