These maps display the changes in density of blue jay observations per person in Pennsylvania over the course of 10 years, sampled at 2007, 2012, and 2017.
A comparison of the three maps indicates a decrease in observations leading up to the present. This potentially demonstrates a decrease in population numbers.
Blue jay observation per person was calculated by taking the total number of blue jays observed in each county and dividing by the total number of observers in the county. This was performed for each sample year.