Wading birds on a dynamic wetland landscape: A synthesis of individual-based modeling methodology

Abstract

The decline in wading birds in their traditional colonial nesting grounds in the Everglades wetland during the twentieth century motivated a series of modeling efforts to understand the dependence of successful nesting by wading birds on the human-altered hydrology of the Everglades. Although habitat quality modeling has helped define the environmental characteristics necessary for wading birds, individual-based modeling is essential to understand how wading birds exploit the dynamic spatiotemporal distribution of prey, which is driven by hydrology during the nesting season. An initial individual-based model, simulating the energetic needs of parent wading birds to raise nestlings, showed the dependence of successful reproduction on the spatial distribution of high prey densities around a nesting site. Modeling at the level of an individual wading bird was subsequently used to understand the effectiveness of different foraging strategies that a wading bird could use to effectively exploit the heterogeneously distributed prey resources during a day. Further spatially explicit individual-based or agent-based modeling ( ABM ) was used to model the daily foraging activity of nesting colonies of many wading birds with individual strategies. This allowed social interactions to be included, showing that both cue-following to find high-quality prey patches and interference within prey patches alter both the daily prey intake and the optimal strategy of the wading birds. The models also showed how social interactions could lead to spatial distributions of foragers that approach ideal free distributions. ABM has been extended to multi-year simulations of wading birds that have the option of annual migrations to and from the Everglades. The models can be used to predict the possible effects of environmental change on migratory patterns. Finally, these models are briefly discussed in the broader context of other wading bird models, although the discussion is not intended to be comprehensive.