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Contiguous grasslands of North America have been converted into a mosaic of forested areas, agricultural crops, urban development, and isolated grassland tracts. Remaining grassland tracts have been stressed or degraded due to the loss or mismanagement of disturbance regimes. Alterations to disturbance regimes creates homogeneous grassland plant communities and allows for the establishment of woody vegetation. Encroachment of woody vegetation may functionally alter grassland-associated communities and displace grassland dependent wildlife. We evaluated the breeding bird community using line transect surveys within nine grazed mixed-grass prairie landscapes. We used non-metric multidimensional scaling to assess breeding bird community level changes to the presence of woody vegetation and used unmarked in program R to determine individual species responses to the encroachment of woody vegetation. We detected 517 individuals of 32 different breeding bird species during the summer of 2016. Community level analysis revealed a shift in the breeding bird community from a grassland dominated bird assemblage towards a woody tolerant grassland and shrub-dominated assemblage as woody vegetation coverage increased. Species level analyses revealed a decline in abundance of two obligate grassland species (Grasshopper Sparrow [Ammodramus savannarum] and Bobolink [Dolichonyx oryzivorus]) as woody coverage increased, whereas, an increase in abundance was determined for one facultative grassland species (Clay-colored Sparrow [Spizella pallida]) as woody coverage increased. In order to conserve grassland bird populations, disturbance regimes and mechanical means must be restored and properly applied to grassland systems in order to remove and control the encroachment of woody vegetation.