What is Abundance?
"Abundance" is the average number of birds reported on all checklists within a specified date range and region. These data tell us what we might to expect when going out birding on an average day. The checklists used in this calculation include those that didn't report the species, providing a measure of relative abundance or how commonly the bird is reported compared to all other species in the region. For example, when looking at data for New York we see that during the week starting 15 May we can expect to find roughly 1 Yellow Warbler while out birding. In contrast, in the same region during the same week we see that zero Rough-legged Hawks, primarily a winter visitor, can be expected in an average day's birding.