I went on a trip into a forest area close by a few days ago to test my new Adaptall-2 adapter for the Tamron 400/4 with aperture control. It was amazingly quiet in there, you wouldn't know the city was only a kilometer away....however, also many mosquitos.
You couldn't stand still for more than five seconds before getting bitten. No wonder I only encountered runners - anybody who was slower didn't make it
Sadly I couldn't see any birds in there, only hear them somewhere above in the trees.
Which led to some experimentation. Under the right circumstances, the 400/4 can be used for some great background separation of more than just animals.
Here I added film grain on purpose in post, without the image somehow seemed unpleasant to the eye. Maybe there's such a thing as uncanny valley for the state between blurry and sharp, like when the bokeh of a lens looks "too busy"?
I encountered a deer, which was probably as surprised by it seeing me as me seeing it. Taken with Sigma DL 70-300mm at 300/5.6 wide open, manually focussed. Sadly it bolted before I could change to my larger lens, I really should get a dedicated holster for the Tamron, but it's hard to find one due to its size.
Then again, it's probably good instinct that caused it to flee once it saw a human lifting a large, heavy object with a lens pointing straight at it....