I'll take that.
1970 is the nice round number where a lot of the earliest best data really comes from. A lot of that is breeding birds survey data. That's one of the federal government programs administered by Environment and Climate Change Canada, and is one of the key citizen science bird monitoring programs in North America. From 1970 onward, that's where we have a huge increase in the number of datasets we can use to pull significant results from. Generally 1970 is that benchmark going back, and lots of studies you see don't often go too far before that, although there are datasets that go longer. The Christmas bird count dataset, as you heard from Geoff LeBaron on Tuesday, is over 100 years old. Within our own database, we have data from Canada going back over 120 years.