Variação temporal na comunidade e na reprodução de aves campestres em áreas queimadas nos campos de altitude no Sul do Brasil

Abstract

Temporal variation in bird community and breeding of grassland birds in burned areas in highland grasslands of southern Brazil Grasslands of South America have been suffering an intense transformation in the last decades, mainly due to the conversion of native grasslands to agriculture or afforestation areas. The correct use of fire, often associated to cattle raising, has been pointed as a form of management to conserve grassland areas over the world. We aimed to assess changes in communities, breeding, and territories of grassland birds over the time, in areas under different histories of fire disturbance in highland grasslands of southern Brazil. Bird communities were sampled through point counts during four seasons (2015 – 2018), while search for nests and territories of Emberizoides ypiranganus and Sporophila melanogaster occurred in three (2013, 2016 e 2017) and two (2016 e 2017) breeding seasons, respectively. We made comparisons of richness, abundance and species composition in different years. Daily survival rates of nests were calculated with MARK program, and territories were measured using the 95% kernel estimator. Richness, abundance and species composition varied significantly in the season of the fire, returning to the initial values (year before the fire) two years after the disturbance. In areas occasionally burned or areas without fire there were differences among the seasons either, but not with an equally clear pattern. Still in the analysis on the communities, of the six species assessed individually for density, three responded significantly to time since the fire. Considering breeding, we monitored a total of 237 nests (178 of E. ypiranganus and 59 of S. melanogaster). Cumulative survival probability and productivity of the nests of both species did not show statistically significant differences among breeding seasons, both in the area burned occasionally and in the area frequently burned. However, the size and number of territories of E. ypiranganus varied over time in the area burned occasionally, with small and less territories in the season of the fire. The number of territories of S. melanogaster was lower one year after the fire in comparison with the season of the fire. In the area with frequent fire there were no changes either in the number or in the size of the measured territories. Our study is the first one to address the temporal dynamics of the effects of fire on communities and important aspects of natural history of grassland birds in southern Brazil. The results allow to know the time taken for the bird community or the territorial parameters of grassland birds to recover after a fire disturbance. Although the results deserve caution in their extrapolation due to the number of areas that it was possible to sample, information about how often fire can be used is important for planning and implementing practices that use fire as a management tool in grassland areas. Further studies should assess long-term effects caused by changes in fire regime, when an area where there was no regular fire becomes managed with fire or when this disturbance is excluded from an area that was often burned