The number of Prothonotary Warbler territories increased steadily for twenty years from 1987 to 2007. At that point, it neared a plateau. 2010 through 2012 saw decreases, due in part to unfavorable weather. In 2013, pring and summer conditions were excellent and the PROWs made a strong comeback to near their peak level in this area.
Note: the large increase from 2005 to 2006 in part reflects the change in survey technique from on-foot only to foot and boat surveys.
The numbers are based on the sites, nest box or natural cavity, that had a pair of PROWs present, i.e., a male and female were observed interacting. For many of these, additional confirmation was obtained based on observations of other nesting activities such as bringing food to the site or removing fecal sacs. In some cases, fledglings were observed before dispersal from the nests.