Hello and thank you for contacting us.
We can't be sure without seeing a sample of the problem to put under the microscope, however aspen trees do commonly get some leaf diseases.
You can prune out the worst affected areas to help the tree recover. There is an option to spray the tree with fungicide when the leaves come out in the spring, but once the leaves are infected, it doesn't help to spray. (So protect the robins, and don't waste your money by spraying now.)
We advise getting rid of the leaves when they fall, so if you are a home composter, leave these leaves out of the pile.
If you want to bring in a sample for more examination, we are at 222 North Havana St. Just south of the baseball stadium at the Spokane Fairgrounds. Our clinic is open 9-3 Mon-Thursday; 9-1pm on Friday, and from April -September, 9-noon on Saturday. You can also call us directly at 509-477-2181.
Thank you for contacting us, and best of luck with your tree.