Although it has been well established that reclaimed surface mines provide suitable nesting habitat for numerous grassland bird species, several studies during the past decade suggest that woody vegetation encroachment is now altering former mine sites (mined ~40-50 years ago) such that they are no longer suitable as breeding habitat for obligate grassland bird species. Though such observations have been reported in the literature and at meetings, few long-term studies examining population trends of grassland birds on reclaimed mines have been undertaken. To this end, the presence/absence of four grassland bird species (Henslow’s sparrows, Ammodramus. henslowii; grasshopper sparrows, A. savannarum; bobolinks, Dolichonyx oryzivorus; and eastern meadowlarks, Sturnella magna) were monitored using 40 point count stations during May, June and July of 2013, 2014, 2015, 2016, and 2018. Colonization and extinction probabilities between each sampling year for each species were estimated using program Presence.
Results/Conclusions
Colonization rates across our study site declined, while extinction probabilities increased for all four grassland bird species. These results mirror declines suggested by count data (unadjusted for capture probability) over the same time period. Habitat analyses conducted during the same period provided strong evidence that shrub species including common yellowthroats (Geothlypis trichas) and song sparrows (Melospiza melodia) were encroaching across the grassland habitats. Future investigations will be designed to determine whether shrub encroachment is the cause for the declines observed in colonization probability and increases in local extinction probability.