To round up this mini-thread on rarity, it might be prudent to ask this simple question - what is rarity? To most birders it is a declaration that the bird in question is of national rarity, and in the majority of the words use, that is exactly what is trying to be conveyed. But it isn’t always the case...
There are three records of Audouin’s Gull from Dungeness, but only two records of Nuthatch. Therefore Nuthatch is genuinely rarer there than Audouin’s Gull. It is also no less rarer than Dark-eyed Junco and Red-eyed Vireo on the shingle. They can all - Nuthatch included - be regarded as rare.
If I am birding in Surrey and see a Gannet sail overhead, I will have found something rarer than a Red-flanked Bluetail on the east coast. These inland seabirds, as numerous as they are on our shores, are so unusual in my home county that I stand a better chance of finding a eastern vagrant on our countries eastern seaboard.
The numbers don’t lie. Rarity is relative. Rarity also changes. My early birding days in north Surrey included regular and unremarkable encounters with Willow Tits. They have now gone. To see one today would be big news, and treated as a rare bird. The flip side to this would be me finding a Little Egret at Beddington in 1975 (I didn't!) That would have caused a big twitch. Today? A birder wouldn’t bother to cross the road to see it.
Those of us who watch inland sites can get our rarity kick in a different way to those who bird the coast. Rarity really is relative. And as much as we don’t bird for rarities sake, it is always the cherry on the cake when we do. We just need to be realistic in our definition of what constitutes ‘rare’.