Determining the impact of livestock removal on avian guilds: How life history traits impact response

Livestock grazing threatens riparian areas worldwide, leading to a decrease in critical habitat for many avian populations.  Currently, no consensus exists as to whether cattle must be removed from riparian areas year-round or whether seasonal removal is equally as effective to improve avian habitat. To address this, we experimentally compared the effects on bird populations of total exclusion vs. seasonal usage on riparian areas in the San Joaquin Valley, California, USA.  Avian species richness and density were measured over five years.  In general, avian guilds with common ecological characteristics, including foraging and nesting behavior, had similar responses to grazing disturbance.  Native species richness and density increased between the 2001 and 2004, with more pronounced effects in total exclusion zones.  Cattle exclusion benefited cavity nesters and aerial foragers but negatively impacted ground nesting species.  A direct comparison with Breeding Bird Survey (BBS) data revealed that observed trends were the effect of experimental treatment rather than a reflection of regional trends.  A long-term monitoring program at these sites will provide ongoing data on the recovery of avian populations over time.