I saw one a short time ago near me in County Leitrim, I thought it was a seagull (!) because of how it looked, but I was assured it was indeed a male Hen Harrier
Yep. From a distant they can look like a pale coloured gull. However, the males have distinctive black "finger-tips" on the end of each wing which makes them quite easy to identify. They'll often swoop down onto groups of birds in fields.