Relationship between grass height, grazing management and avifauna in livestock systems in the eastern region of Uruguay

Doctoral thesis abstract

Abstract

In the natural grasslands of the Río de la Plata, where livestock production can coexist with biodiversity, effective pasture management practices play a critical role. This study combines two approaches to shed light on the relationship between livestock management and bird species. The first study analyzes birds' responses to various variables influenced by livestock management. Field data were collected and 69 bird species were analyzed across 454 paddocks on 46 properties in the eastern region of Uruguay. We found that artificial grasslands had a negative impact on many bird species, while the presence of tussock patches (grasslands) was associated with positive effects, especially in endangered species. Grassland specialists exhibited sensitivity to grass height, responding positively to tussock patches but negatively to tree coverage. Adjusting livestock stocking rates to control grass height emerges as a valuable tool to promote grassland specialists. The ideal scenario for bird biodiversity involves a mosaic of native grasslands, both short and tall, interspersed with tussock patches and trees. Additionally, we found that species-specific responses were influenced by bird traits, such as body size and foraging behavior, enhancing predictive capacity for pasture management. The second study focused on assessing bird responses to changes in management on six properties to increase grass height, thereby improving dry matter intake by livestock and potentially increasing livestock production. Although the average grass height increased from 6 cm to 12 cm, bird abundances and species richness did not vary. However, since the abundances of the assessed species remained constant with increasing grass height (and thus, available dry matter for livestock), we conclude that it is possible to protect a subset of grassland specialist birds while potentially increasing livestock production.