ALBANY — Nearly 2 million robins ruled the roost in the 2010 Great Backyard Bird Count, outnumbering all other species in the 13th annual tally of North American birds reported by 63,000 volunteer bird watchers.

Organizers say the large number of American robins was mainly because of a massive roost in St. Petersburg, Fla., where birders reported 1.4 million during the four-day event in February. The count also showed a dramatic increase in tree swallows.

The count helps document changes in the number and distribution of birds over time.