Foraging Wading Bird (Ciconiiformes) Attraction to Prescribed Burns in an Oligotrophic Wetland


Many wetland communities are fire prone or fire dependent, especially those dominated by forbs and grasses. Despite our considerable knowledge about fire effects on wildlife in uplands, there is a relative paucity of information about effects of fire in wetland systems. Long-legged wading birds (herons, egrets, ibises, storks, spoonbills; order Ciconiiformes) may benefit from fire through the exposure of prey after vegetation removal, or through a trophic response of prey to increased availability of nutrients and increased light. We conducted aerial surveys of foraging wading birds in prescribed burns and adjacent unburned areas in the central Everglades, Florida, USA, to determine if wading birds select for burned habitats. We measured aquatic prey density in burned and unburned sawgrass (Cladium mariscus [L.] Pohl ssp. jamaicense [Crantz] Kük), and densities of prey injured or killed in the fires. We also observed foraging great egrets (Ardea alba L.) in and adjacent to prescribed burns to determine whether foraging success (i.e., capture efficiency and capture rate) differed between burned and unburned areas. Great egrets and white ibises (Eudocimus albus L.) selected for burns and areas of deeper water adjacent to burned areas, and avoided dense, tall, unburned vegetation. Measured densities of prey killed by the fire were very low. Live aquatic prey densities did not differ between burned and unburned sawgrass. Great egrets had higher capture rates in sloughs adjacent to burns than in burned areas, but were more efficient at capturing prey in burned areas than in adjacent sloughs. Prescribed fires created short-term shallow water habitats (burned areas) with limited submerged and emergent vegetation, making prey in burns more vulnerable despite lower densities (availability) compared to adjacent sloughs. This research suggests that prescribed fire in grass-dominated wetlands may attract predators like wading birds primarily because removal of vegetation makes prey easier to capture.

Fire Ecology