Grazing differentially affects both the abundance and breeding success of grassland birds (e.g., due to differences in bird species' preferences for sparse or dense vegetation structure, nest predator response to grazing, and/or trampling of nests). Coupled with prescribed fire, grazing impacts can be compounded by pyric herbivory—the preference of grazers to choose newly-burned sites in which to graze. The purpose of this study was to determine how a recent re-introduction of American bison (Bison bison) coupled with prescribed fire may impact grassland bird nests. Artificial nests were used to determine if grazing and fire impacted nest success, total mammalian depredation, and depredation by the most common nest predator, mice (Peromyscus spp.). Artificial nests were placed in sites with and without bison before (2014) and after bison re-introduction (2015–2018); sites had fire return intervals from 1–2 y. We found the re-introduction of bison had a negligible influence on nest success and total mammalian depredation. However, nest success was lower in burned sites compared to unburned sites. The decrease in nest success correlated with an increase in total proportion of depredation events in burned sites compared to unburned sites. In addition, the proportion of Peromyscus spp. depredation events was marginally higher in burned sites compared to unburned sites. Although predation by Peromyscus increased after bison re-introduction, prescribed fire differences drove this change. Our results suggest prescribed fire may increase nest predation of artificial nests, indicating a possible impact on ground-nesting grassland birds. In contrast, bison had a negligible impact on artificial nest success in the first 4 y following their re-introduction.
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Vol. 184 • No. 1