I think this is the thing with wildlife - you sometimes have to stay very still and I find it hard hand holding and staying in position. I find it especially hard with the extender on the 300mm.
I once ended up half crouched holding my Oly kit whilst photographing a hare. I had been about to get low on the floor when it turned my way. I stayed in that position, half squatting, whilst it fed and I photographed.... everything was twitching and wobbling in the end as I tried to maintain my position

and this is light compared to your lens (which I am very envious of!)
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