Finding solutions for bird restoration and livestock management: comparing grazing exclusion levels

Abstract

Riparian habitats in the western United States support high avian abundance and diversity and are important areas for livestock grazing, although grazing contributes to the degradation of riparian vegetation. Complete removal of livestock is generally the most beneficial for bird communities, but alternative management approaches allowing for seasonal livestock grazing may also increase avian habitat quality. Determining management approaches that integrate conservation priorities and human use has the potential to improve conditions for birds across many grazed landscapes. We anticipated that both the full and seasonal exclusion of cattle from riparian areas would result in the recovery of avian populations. To test this, we experimentally compared the effects of total cattle exclusion vs. seasonal usage on bird populations in the riparian areas of two creeks in the San Joaquin Valley, California, USA. Avian species richness and average abundance were measured over six years, from 2001 to 2006. In general, native avian abundance and richness increased in both full- and seasonal-exclosure areas, with increases compared to the pretreatment year for all years except 2005. Habitats that had complete cattle exclusion recovered more significantly, with 29% lower avian abundance in seasonally grazed habitats. There was no significant difference in avian richness between the two grazing treatments, although richness did increase over time. In addition to increases in native species, abundance of nonnative birds and brood parasites also increased significantly, with a greater avian abundance in the full-exclusion areas. A direct comparison with the Breeding Bird Survey (BBS), to further investigate annual avian population trends, explained the native species decline in 2005. This comparison revealed that observed trends were the effect of experimental treatment rather than a reflection of regional trends. Although the overall trends indicate that the full exclusion of livestock from riparian areas results in more abundant bird populations, seasonal exclusion is also a successful method for avian recovery. Land managers should consider both options in riparian areas, selecting full cattle removal for avian management only and seasonal cattle removal for situations where incorporating conservation and land use practices is advantageous.