Maguari Stork Nesting: Juvenile Growth and Behavior

Abstract

Although it has a wide range in tropical South America, the Maguari Stork (Ciconia maguari) is poorly known. In an 11-yr study of its breeding biology in the llanos of Venezuela I found the mean clutch size for 3 yr to be 3.2 eggs. The young hatched asynchronously at 29-32 days and usually made their first flight at 60-72 days. Data on egg sizes, weights, and a probable dump egg are given. The weight and growth of two siblings, plumage succession, and nestling and fledgling behaviors are described. The fledging success of eggs from 55 nests, over 9 yr, was 61%. Loss of eggs (presumably from snake predation) was higher than nestling loss. Although the asynchronously hatched young in a clutch varied greatly in weight and continued this difference throughout nestling life, no case of brood reduction was found in 123 nests during the study. Nestlings were fed mainly frogs and tadpoles, fish, eels, and aquatic rats; food classes and food sizes brought by adults varied with the age of their young. Maguari Stork nestlings do not grasp with their hallux and so are confined to their nests until they can fly. I suggest that the two black plumages of nestlings, between the white hatching down and the white first basic plumage, are for crypsis of the nest-bound young.