I see Corvus cornix all the time in Estonia. I literally have 30 of them sitting behind my house most of the time. Is that enough evidence to go to the Estonia place page and set occurrence to “common”, or does that require more scientific methods of determination?
More generally, how is the level supposed to be determined? I didn’t find documentation for it (but I might have missed something).
I think sure it’s enough if the species occurs everywhere/almost everywhere in the country (in right habitats) to call it common. I’d say that the only part that gives birth to questions is uncommon/irregular, but as one is closer to common for me it’s just something that lives there but you don’t find it every day while irregular can be applied to species shown for some years only or migrating species that sometimes seen but not too often. For exampe this fall we had White-winged Crossbills in Moscow, they just come here for winter, so I’d call that abundance irregular. Harder to say for rare species that always live at the spot. The system of grades seems not ideal.
A few people use place lists and even fewer set up occurances for most of species. =(
Since there are 55 RG observations for Estonia at the moment, and the mapping shows them as widespread, and in the virtual centre of its range geographically, I’d say it warrants at least “present”, and I’ve marked it as such. I’m not sure how you’d determine commonality, either. Someone who knows more about birds generally may be able to answer that.
I don’t believe there is any documentation or guidance for the Occurrence Status Level choices. So for now the choices like common, uncommon, and irregular are subjective labels of convenience. Since any user can change them at will, I’m not sure I would put a lot of work into curating them for a place, unless it is a special community place or checklist that I created for my own use.
Edit: apologies @kitty12, I meant that to be a reply to the whole topic, not specifically to your post 
No worries @jdmore. I read it as a continuation of the conversation.
I usually just go with “present” if there’s one or more RG observations in a particular geographic region.
I’m no expert, but I don’t think it’s so simple… for instance, organisms with high mobility might end up far out of their natural range once in a long time, eg a single bird blown away by a storm. So unless there is some corroborating evidence, like a relevant range map or multiple Observations over a period of time, you may want to wait on that.
I think that is probably one of the intents of the “irregular” category.
Even irregular is not granular enough for birds. Many bird checklists define irregular and unexpected/accidental as 2 different things. Black-throated Grey Warbler is irregular in Ontario. Consistently it is seen in very low numbers (typically less than 5 per year) in the province. Swainson’s Warbler is accidental and considered unexpected.
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