Orinoco Goose Oressochen jubatus
Version: 1.0 — Published March 8, 2013
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Timing of reproduction in the Orinoco Goose varies depending on geographic location and rain patterns. Orinoco Geese in the southern hemisphere nest between April and November, with peak occurrence of fledglings during the dry season, around July-August in Peru, and somewhat later (August-September) on the Rio Juruá, Brazil. Some authors (Gómez-Dallmeier and Cringan 1989, Hilty 2003) suggested that in Venezuela most birds nest in wet season (July-August), and only some in the dry season (beginning December to January). However, Kriese (2004), over 3 years, found birds in the Venezuelan llanos to nest exclusively in the dry season, typically beginning in November-December and completed by March. Orinoco Geese may compete with other birds such as owls and parrots for nest cavities (Hilty 2003 and Meneses, personal communication).
Kriese (2004) studied natural and artificial nest use in the llanos of Venezuela and found that they preferred cavities that were large in size, with trees of DBH > 30 cm required to accommodate a nest. Further, Kriese found that Orinoco Geese did not use abandoned cavities of primary cavity excavators, but rather required other natural processes to create cavities, such as limb loss, wood rot or termite activity. In Venezuela, females preferred nests at approximately 3 m height, and close to water. Natural cavity nests that were depredated or abandoned were never used in subsequent years, although artificial nests were repeatedly used regardless of reproductive success or failure. The main cause of nest failure was predation, with Black-eared Opossums (Didelphis marsupialis) the most commonly observed nest predator. Orinoco Geese engage in intraspecific brood parasitism, and Kriese found that nest success was higher in nests that were parasitized than those that were not. Mean clutch size of parasitized nests was 18.6 eggs (± 3.0, n = 9) vs. a mean of 7.3 (± .9, n = 9) for nests that were not parasitized.
The species also has been reported to lay its eggs on the ground, in areas densely covered by grass and other annual plants close to rivers or wetlands (Sick 1997), although this seems to be an unusual reproductive behavior for the species.