On Wednesday, the 10th Circuit Court of Appeals held that regulation of takes of the Utah prairie dog, 
a purely intrastate species, does not violate the Constitution. Reversing the decision below, the 10th Circuit joined all four other circuit courts to have dealt with the issue thus far in upholding the ESA against such Commerce Clause challenges.
I will note that I predicted this outcome when the District Court case was decided, though I can’t claim that much credit. As the Court noted, more than 2/3 of protected species are purely intrastate. Moreover:
Because a species’ scientific or other commercial value is not dependent on whether its habitat straddles a state line, Congress had good reason to include all species within the protection of the Act. It did not behave irrationally by taking the broader approach.
Given the absence of a circuit split, I don’t see the Supreme Court taking this case. I do hope that People for the Ethical Treatment of Property Owners keeps fighting the good fight, though. I just love that name.