What decides suggestion order in ID dropdown list?

Yes, I used to type ‘bi’ and birds appeared second on the list. Now ‘bi’ doesn’t show birds in the top ten. Typing ‘bir’ doesn’t even show birds in the top 12, and even when I type ‘bird’, birds is number 8 in the list.
Given how often I (and I suspect others) want to search for birds, I agree it would be useful to have them higher on the list.