Not an ideal lens for birding / wildlife, even though it would get you close to your subjects. Mirror lenses tend to be very slow & pretty much useless in low light conditions. They also produce doughnut shaped highlights in the brighter parts of the image. While I haven’t used this particular lens, I would be more inclined to get a normal “non-mirror” type lens.
I had a mirror lens for a while, and got some nice shots from it too, it does have its downside
though and I am not talking about the “doughnut” highlights which I didnt mind at all (love hate thing)!
But you do need good light as it is fixed at f8, so not ideal for Ireland and our fantastic weather :lol:
I would save your money and buy something quicker, might take you longer but in the long run you will
be glad you did. I would aim for a 70-200 2.8 and use a converter to extend your focal length, you dont
say what camera you are using but if it is a crop sensor you would already benefit from the 1.6 extra
length that the crop sensor gives.
You can never get close enough in my experience. If your pocket can stretch to it , a Sigma 50-500 mm (non OS) or 150-500 mm OS, new or second hand can yield great results.