Could work a bit like the checklist report in that all species could be listed on the left and then years across the top. In each year the species has been seen the little box could be coloured in and in the years the species wasn't seen it would just be the box outline. Scroll down to see the whole list of species, scroll across to see all years. Filters could include years so you could select a start and end year ie. 2010 to 2020 if you don't want to see 30+ years - another toggle could be to show all species (even the ones you have never seen) or you could toggle this to exclude all species you have never seen. A further toggle could be used to include "heard only" in the report

This report would allow you at a glance to see what species you haven't seen in the current year compared to previous years and therefore how long its been since you have seen a species