Fire ecology and bird biodiversity in southeastern Minnesota

Background/Question/Methods

The conversion of grasslands to agricultural lands and the overgrazing of livestock have caused a decline in the area covered by natural prairies in the United States, which in turn has caused a decline in the populations of bird species that use grasslands for breeding and as stop-over sites.  Efforts to restore lost prairie often involves simulating natural burn cycles.  On the St. Olaf College Natural Lands in southern Minnesota, the prairie is burned in sections, creating a mosaic of different habits, ranging from primarily grasses to primarily forbs.  To determine whether differential burn cycles increase biodiversity and benefit grassland birds, I studied birds on five sections of prairie burned in four different years (2010, 2012, 2013, and 2014).  Mist nets were used to capture birds which were then banded with federal aluminum bands.  Birds were also aged, sexed, measured, and then released.

Results/Conclusions

During the banding period, 23 species of birds were caught in the five different sections sampled, 11 of which were sparrow species.  While the four most common sparrow species showed a preference for more recently burned prairies, the trend wasn’t significant.  When considering all bird species, however, Simpson Diversity Index values revealed a significant difference between two sections of prairie burned in 2010, and between one section burned in 2010 and one in 2014, suggesting that differences between the sections – likely the biodiversity of plants – enhances bird diversity.  There was also a significant difference in the number of birds caught in different sections during different two-week time periods.  From 13 Sep - 27 Sep, birds preferred the most recently burned section of prairie, from 28 Sep – 11 Oct they more evenly occupied all sections of prairie, and from 12 Oct – 27 Oct they preferred the section burned in 2012 while largely deserting the sections burned in 2010.  These results suggest that burning smaller sections of a prairie benefits migrating birds.  Since different burn sections are occupied by different species, and since different burn sections are occupied differentially at different times, it appears that providing a mosaic of habitats promotes diversity.