Productivity and habitat modeling of wood storks nesting in North and Central Florida

Abstract

Rainfall, surface water levels, location within the state, and area and types of habitats (n = 29) surrounding wood stork Mycteria americana colonies in North and Central Florida were analyzed at 10-km, 20-km, and 30-km radii around each colony to examine their relationship with fledging rate and number of nests during 2003-2005. Seven variables within 10 km, 14 variables within 20 km, and 6 variables within 30 km of colonies were correlated with fledging rates. Fledging rate and number of nests were significantly associated with both wetland and nonwetland area and habitats. Among all the variables, fledging rate was most strongly associated with rainfall during the preceding 12-24 mo. Both larger colonies and colonies in North Florida had higher fledging rates. Although some variables had a positive association and other variables had a negative correlation with fledging rates, results were not consistent across all three radii, which suggests that the effects of hydrologic and habitat variables differs with increasing distance from a colony. The size of a wood stork colony was sensitive to a larger number of variables and varied by distances from the colony. Colonies were smaller in the northern part of Florida, and coastal colonies were larger than interior colonies. Because wood storks often use ephemeral foraging sites closer to a colony early in the season and those sites may not be available later in the season, wood storks may shift to alternate, more distant sites and habitats later in the season. A hypothesis is proposed whereby wood storks establish their colonies using proximate clues of prey availability based on the effects of past rainfall and certain preferred habitat types. These proximate cues to prey availability and foraging substrate surrounding a colony are detected by wood storks before the onset and during the initial nesting season. However, the long-term stability of a colony may ultimately be determined by yearly rainfall patterns and habitat variables at larger distances and by fledging rates that contribute to recruitment of nesting birds and an increase in number of nests.