Surface animals in dwarf fortress are kind of boring. There’s often only one or two “clusters” of animals on the map (either one group of animals, a lone animal, two lone animals or a group and a solitary beast), and they’ll often remain there for so long that some of them might die of old age or bear children.
Not to say I mind some animals being present year round (like this is where their den is or something) but it should definitely be possible to have more “clusters” of surface animals present on the map at the same time, rather than just one and very rarely two.
Migrations should also be more frequent, because I’ve had giant cockroaches remain on my map for so long that they died of old age, and I’ve witnessed carps bear fry, only for those fry to grow into adults.
Frequencies and population numbers should also be adjusted. You run into the same ones wayyy to often. I’m not saying that some animals shouldn’t be rarer than others, or that every region needs to have every possible animal appear in it, but some animals are far too frequent and others are far too rare for my taste (this is also applicable to the underground, *cough* crundles *cough*).
Finally this doesn’t have much to do with the topic at hand but not every underground animal should just attempt to rush down your fort the moment they spawn in. I can understand giant cave spiders being attracted by the yummy dwarf scent and stuff but even things like elk birds and plump helmet men do it.