I will add:
* Birding-by-ear recordings to identify birds by song. These come in various formats.
* Does your friend like squirrels? Get a squirrel-a-gig. Do they hate squirrels? There's no such thing as a 100% squirrel-proof birdfeeder, but the gravity models come close.
* A birdbath of basalt or other dark stone will keep water liquid longer using passive solar heat.