Breeding is highly synchronised with the onset of rain during the wet season, which usually lasts from May to November in the llanos of Venezuela. However, most breeding of the maguari stork happens from July to mid-September, which is earlier than breeding in both the sympatric wood stork and the jabiru. Individuals begin migration to the breeding grounds as the rains begin, although some individuals may migrate and arrive early just before the rains. Despite the lengthy wet season in the llanos, the nesting period in one year never lasts for over four months. Elsewhere in the stork's global range, the timing of the breeding season is slightly different and somewhat shorter. In north east Argentina for example, the breeding season extends from June to August; and in east central Argentina extends from July to October, with eggs probably being laid in late June and early July. On Isla Mexiana in eastern Brazil, the breeding season lasts only from August to September. The timing of onset of the seasonal rain is extremely variable across the maguari stork's global range, with rainfall beginning in some years as early as late March and others as late as June. The start of breeding is therefore correspondingly variable; and in Argentina, nesting may commence as late as August with late rains. In the llanos, breeders may lay eggs as early as late May following unusually early and heavy rainfall; whereas young breeders may lay eggs as late as October with late-arriving rain.
