A biological atlas maps the distribution, and sometimes the abundance, of a group of species (most commonly breeding birds) within a defined geographic area during a set time period. These atlases have dramatically advanced distributional studies over earlier ones based on randomly collected specimens or anecdotal observations by attempting to obtain comparable coverage within each (or a random sample) of the equal-sized blocks in an atlas grid overlain on the study area. The first breeding bird atlases began in Britain and Ireland in the mid-1960s (Lord and Munns 1970, Sharrock 1976). The concept quickly spread throughout the world but has been applied mostly in the northern hemisphere (Dunn and Weston 2008). The first atlas project in North America, for two counties in Maryland, was initiated in 1971 (Klimkiewicz and Solem 1978), but most subsequent work has been conducted at larger scales. From 1979 to 2018, atlases have been completed for 9 of Canada’s 13 provinces and territories, of which 6 have completed second atlases. They have been completed for 41 of the 50 United States, of which 18 have completed second atlases (Beck et al. 2018).