or 3rd egg is laid, is carried out by both parents, and lasts 29–32 days. The eggs are oval or subelliptical, and mean egg measurements are 75.19mm in length and 52.56mm in width; with maximum egg measurements of 77.4mm in length and 56.2mm in breadth having been recorded. The eggs are also said to be disproportionately small compared to the laying female's body mass. Weight differences between different-aged siblings have been recorded as 500-1400 g. Egg laying is however highly synchronous between nests in a colony, so that relatively large groups of young from different nests fledge together in batches toward the end of the wet season. This may serve as an anti-predator strategy to dilute an individual's risk of being predated. As adults, male maguari storks become sexually mature at three years of age, and females at four years. After three weeks of age, maguari stork nestlings develop defensive behaviour if their nest is approached by an intruder; which is not known for nestlings of other stork species. They crouch forward, partially spread their wings and erect the black feathers on their head, neck and back; followed by a shrill, rasping scream and an attempt to grab a persistent intruder with their bill. In many other stork species, akinesia lasts throughout much of the nestlings’ early life, and the constantly white plumage makes them appear as eggs to potential chick predators. However, in maguari stork nestlings, akinesia ceases much earlier, and the unusual aggressiveness of the young has probably developed as a specialised anti-predator strategy in compensation for the young chicks’ inability to leave the nest due to their slow-developing hallux and the vulnerable position of the nest on the ground. However, at 25–35 days old, the hallux is sufficiently developed to allow the chicks to leave ground nests in search of food. Chicks also occasionally beg for food from their parents outside the nest, but parents have never been observed to feed their young outside the nest. There appears to be little sibling rivalry in maguari stork nestings, with most nestling mortality being due to young falling out of nests containing 3-4 chicks; and egg mortality primarily through predation appears to be higher than chick mortality. The large congregations of maguari storks in the pre- and post-reproductive periods are considered a reliable indicator that this stork breeds locally in the area in which the groups are sighted. Threats