Squirrel portrait... new lens is looking good!

I've been frustrated at not being able to get as CLOSE to my garden creatures as I'd like, so I ordered a new lens recently and am trying it out... this is one of the first really good close-ups of one of the MANY squirrels regularly visiting my garden to raid the feeders. He is sitting on my warped deck rail and taking a break from trying to get in to one of the feeders. He's just picked up some stray seed dropped onto the deck rail by one of the birds.

The lens is a Nikon mount - Sigma 120-400mm f/4.5-5.6 lens with OS (Optical Stabilization). This image was shot hand-held from inside through my kitchen window... the lens is pretty well balanced for hand-holding as long as there is plenty of light. I also purchased a 1.4 teleconvertor... using that requires a tripod for sure! One day soon I hope to sit in the back yard with the tripod set up and the new lens + teleconvertor assembly. The birds don't really like me pointing this huge lens at them (even from INSIDE) so I'll have to bide my time until they get used to it AND me in the garden or I won't get any shots at all. My yard is too tiny to set up a blind of any kind.