Nesting Dynamics of Four Ardeid Species at Subregional Scales: Recovery Rates after Sudden Major Declines in Nest Abundance

Abstract

The functional roles of nesting heron species (Ardeidae) as top predators in regional wetland landscapes may be sensitive to variation in nesting abundances at subregional scales corresponding to available habitat for nesting and foraging within individual wetland subsystems. This study investigates the dynamics of annual nesting abundances of four ardeid species within 10 major wetland subsystems of the San Francisco Bay Area, California, USA, during 1991–2010. Interrupted time series analysis was used to measure impact and recovery rates related to sudden major declines in nesting abundance below selected thresholds of annual change. Year-to-year persistence of initial impacts was above 78% for Great Blue Herons (Ardea herodias) and Great Egrets (A. alba). Snowy Egrets (Egretta thula) recovered more quickly, with 63–66% annual carryover of initial impacts. The time required for 95% recovery averaged 18.8 years for Great Blue Heron, 13.0 years for Great Egret, 7.2 years for Snowy Egret, and 14.5 years for Black-crowned Night-Heron (Nycticorax nycticorax). Most of the major subregional declines in nest abundance were associated with impacts at a single colony site. The results highlight the significant effects of sudden major declines in nesting abundance on the status of ardeids within individual wetland systems across a larger regional wetland landscape.