Abstract

Weekly, during the reproductive season of 2003 and 2006, a White-necked Heron (Ardea cocoi) colony was studied on the western shore of Santa Elena lake, in the province of Nuble, Chile/The herons constructed all their nests on willow trees (Salix babilónica) in standing water with reeds (Junáis spp.). The first eggs hatched between the 21st and the 30th of September (start of spring), with an estimated incubation period of 27 days (range: 26-29 days). Nests were abandoned between the first week of November (mid-spring) and the last week of January (mid-summer). The herons showed tolerance with other nesting species in the area but conflicts with Black Vultures (Coragyps atrattus). The structure, size, and localization of the nest is described. The oval nest had mean external dimensions of 92.2 cm in length × 72.3 cm in width, and 45 cm in height. The mean dimensions of the inside of the cups were 34.5 cm in length, 31.0 cm in width, and 8.5 cm in depth. The mean distance between neighboring nests was 9.5 m. Of the 64 eggs monitored, 55 hatched. The mean dutch-size was 2.4 eggs/nest; their mean weight was 75.1 g. The mean number of successful hatchlings was 1.7/nest. © The Neotropical Ornithological Society.