Even though you might not be able to see a reflection the bird probably was and their vision is different than humans. Northern Cardinals are well known for pecking at themselves in a variety of reflective surfaces. These articles advice on how to get rid of the reflection during this period of year.  Since he is still living you'd want permission to set up an eBird account on his behalf. You may need volunteers from a local birding club to band together to get all the checklists data entered in. It is often too time consuming for one person to accomplish.   A Bird Keeps Flying into my Window or Car Mirror, on Purpose. What Should I Do? We usually see this behavior in the Spring—the time of year when most birds establish their territories, find a mate, lay eggs, and raise young. To ensure success, they defend their territory aggressively, and will attack and try to drive away any bird they view as a possible competitor or a threat to their young. When they see their own reflection in your window or car mirrors, they assume they're seeing a competitor and attack the image. We sometimes see this at other times of year as well—less frequently. This behavior usually dissipates within a few days or, at most, weeks. But while it lasts, the bird may exhaust or even hurt itself, and it distracts the bird from far more important activities. Plus, this behavior can be extremely annoying for the people witnessing it. To get rid of the reflection, you must alter the reflective surface. You can cover it with fabric, or newspaper--or a tarp. When you're no longer seeing the bird nearby you can remove this. Often, rubber snakes frighten birds away, at least temporarily—although like any object that doesn't move, the birds get used to seeing them. There are a host of other things to try at: https://www.allaboutbirds.org/news/why-birds-hit-windows-and-how-you-can-help-prevent-it/ and here: https://abcbirds.org/get-involved/bird-smart-glass/