RESOURCE USE BY HERONS IN A YUCATAN WETLAND DURING THE BREEDING-SEASON

During 1986, we studied the habitat, prey type, and prey size used by six species of egrets and herons in the Sian Ka'an Biosphere Reserve ( Yucatan, Mexico). The availability of different habitat types, which v aries from salt to freshwater and from open to forested wetland, allow s the herons to segregate into two groups (1) Great Blue Heron (Ardea herodias)-Great Egret (Casmerodius albus)-Snowy Egret (Egretta thula), that use mainly freshwater habitats, and (2) Reddish Egret (E. rufesc ens)-Tricolored Heron (E. tricolor), that use marine habitats. We have no data for Boat-billed Herons (Cochlearius cochlearius), because thi s species is strictly nocturnal, and censuses were conducted at daylig ht. Prey type and prey size greatly differ among Great Blue Herons, Gr eat Egrets, and Snowy Egrets but overlap considerably between the Redd ish Egrets and Boat-billed Herons. We found a positive correlation bet ween size of heron and size of prey, but in our study area prey size i s not important in niche segregation, since four of these species eat prey of similar sizes.