Random brainstorm for you. Take all these with a grain of salt.
Further existing milestone suggestions:
Record 50,000 observations – there are enough users far beyond this point and it’s a reasonable goal to aim for.
Record 100 observations with sound – encouragement of submitting audio observations is great.
Observe 100 species with less than 100 total observations – this is a reasonable extension.
Observe 50 species with less than 10 total observations – some people I’m checking have over 500-1,000 species with <10 obs, so it seems fair. Keeping it low so it is reasonable for all geographic areas.
60-day observation streak – a natural extension of the existing goal, but not so insane no one can reach it easily
Observe 500 total status species – a combination goal of vulnerable, threatened, near threatened, endangered, and critically endangered species.
New suggestions:
Participate in a City Nature Challenge (would use date ranges, and maybe locations, not sure how you’d do it. Project participation?)
Participate in 3 City Nature Challenges
100 Comments on observations.
Observe 25 fern species (and if you take this and the following, change 100 plants to 150 plant species).
Observe 25 bryophyte species.
Changes to existing values:
Observe 100 animal species → Observe 500 or 1000 animal species (this already includes several existing 100 species achievements and so just 100 feels too low a milestone).
Observe 25 snake species → Observe 20 snake species, 25 is a very high requirement for many parts of the world.
Observe 100 insect species → Observe 150 or 200 insect species (already includes 100 for Lepidoptera, and this is one of the two highest diversity groups for observation).
Observe 25 raptor species → Observe 15 or 20 raptor species (25 is a quarter of the 100 bird goal, and not all regions have much raptor diversity, so it doesn’t seem fair).