Fire and grazing have influenced Great Plains prairie communities since the last glacial retreat. European colonists changed the timing, frequency, intensity, and quality of these disturbances. These changes may pose problems for grassland bird populations, which have also suffered from habitat conversion. We employed an experimental approach to observe the effects of fire on grassland bird populations. In 2006 and 2007 we surveyed breeding bird communities at 24 points at the Grazinglands Research Laboratory at Ft. Reno, Oklahoma, where fields are burned every few years to promote cattle forage. We conducted one 10-minute 100-m radius count at each point during each of two breeding seasons Six of these points were in fields that were burned in April 2007. For burned and unburned groups of points, we calculated the ratio of the mean abundance per point for each of three obligate grassland-breeding species in 2007 to the mean abundance per point in 2006. If fire affects the abundance of a species in the succeeding breeding season, we would expect this ratio to differ between burned and unburned fields for that species.
Results/Conclusions
Although mean abundance of dickcissels (Spiza americana) declined from 2006 to 2007 at unburned points, mean abundance increased between these two years in burned fields. The between-year ratio for this species was thus higher in burned fields than in unburned fields. Bootstrap analysis reveals this difference is statistically significant. Counts for eastern meadowlarks (Sturnella magna) and northern bobwhite (Colinus virginianus) were lower the second year. This may simply reflect later survey dates during 2007, resulting from flooding and other logistical constraints. Between-year ratios of meadowlarks and bobwhite were lower in burned than unburned sites. These data suggest frequent burns may increase abundances of some grassland-obligate bird species (such as the Dickcissel) in the year following a fire. Other species (such as the meadowlark and bobwhite) may decline in the season following a fire. More data are needed to draw firm conclusions. We will continue to monitor bird populations in these fields before and after prescribed burns and throughout the fire cycle in order to understand how fire affects grassland bird populations.
