NATURAL AND EXPERIMENTAL INFECTIONS OF EUSTRONGYLIDES-IGNOTUS - EFFECT ON GROWTH AND SURVIVAL OF NESTLING WADING BIRDS

One of three Tricolored Heron (Egretta tricolor) nestlings experimenta lly infected with Eustrongylides ignotus larvae died two days postinfe ction. During eight days postinfection, the other infected birds consu med less food per meal, consumed less food in relation to body mass, r egurgitated more frequently, and exhibited lower bill and mass growth rates than did three uninfected control birds. Prevalence of eustrongy lidosis among free-ranging Great Egret (Casmerodius albus) nestlings f rom Lake Okeechobee ranged from less than 5% in 1989 and 1991 to 28.4% in 1990. During 1990, infected nestlings suffered 10.6 to 17.9% highe r mortality than uninfected birds, with younger nestlings suffering pr oportionately greater mortality. Summarized across colonies and nestli ng ranks (i.e. hatching order), infected nestlings averaged 2.9% short er bills, 4.1% shorter tarsi, and 6.9% shorter wings than non-infected birds. Among rank 1 (oldest) and 3 (youngest) nestlings, infected bir ds were lighter (6.3-9.0%), but among rank 2 nestlings from both colon ies infected birds averaged heavier than their noninfected counterpart s. These results for mass may be due to the interactive effects of sib ling rivalry. Eustrongylidosis generally had the greatest impact on th ose nestlings otherwise disposed to lower growth rates, whether due to colony location or nestling rank. The results emphasize the importanc e of monitoring diseases whenever prefledging growth and survival are of interest.