The impact of cattle grazing exclusion on riparian birds

Oak titmouse, (Baeolophus inornatus), consistently dominant species in seasonally excluded riparian areas in the study. Credit, Velo Steve.Past research has shown that cattle grazing can have negative impacts on birds. This is particularly true in riparian areas, important avian habitat, where browsing and trampling by cows can alter the vegetative community and negatively impact the functionality of the ecosystem.

This has led to efforts to restore riparian habitat by excluding cattle grazing - an approach which has been shown to increase avian abundance and species richness.

However, given that much riparian habitat exists on private agricultural land, the question arises whether alternative approaches can be taken to similarly improve avian habitat through management of cattle in the riparian area, while allowing some grazing activity that can generate an economic return for the landowner.

A research team lead by Kara Nelson of the Nature Conservancy addressed this question by comparing the benefits to birds from two different approaches to managing grazing in the riparian area: one that excluded cows entirely and another that only allowed access during the winter months.

They conducted their study from 2002-2007 on the 32,986 acre Simon Newman Ranch in central California - a recently conserved property in which historic grazing since at least 1850 has led to "the loss of riparian vegetation and severely reduced recruitment and hedging of riparian trees and shrubs."

The study, published in the journal Ecological Applications, found that both treatments significantly increased avian species richness and abundance compared to baseline levels for all years except 2005.

A comparison with results from the Breeding Bird Survey showed that annual population trends were likely responsible for the 2005 decline.

Completely excluding grazing appeared to have a greater positive impact - avian abundance was 29% lower in the seasonally restricted areas. The study findings suggest that habitat improvements from full exclusion of cattle occur more rapidly.

However, species richness was similar under both treatments. Furthermore, the excluded areas had a greater abundance of invasive birds and the parasitic species, the brown-headed cowbird.

Interestingly, the seasonally grazed areas displayed a more dynamic avian composition with a greater number of dominant species (27) over the 6-year period compared to fully excluded areas (10). Based on the overall findings, the authors write,

"For management situations where allowing some livestock grazing is desired or avian recovery can occur more slowly, our study demonstrates that the timing of cattle presence in riparian areas can effectively allow for both grazing interests and recovery of bird populations. This approach may also be applied across working landscapes with important bird populations and habitats, where complete livestock removal may be unrealistic."

--by Rob Goldstein

Nelson, K., Gray, E., & Evans, J. (2010). Finding solutions for bird restoration and livestock management: Comparing grazing exclusion levels Ecological Applications DOI: 10.1890/10-0032