This is a superb lens for birding and will also do close ups. It is a 600mm full frame equivalent. When matched with an OM1 the birhd subject identification means you get rapid and reliable focus on flying birds. I have also used it with a 1.4 converter, with bird tracking. That setup works amazingly well.
I filled a 64Gb card on my last outing using this lens with the OM procapture feature because the quality of results is superb and addictive