Natural history and breeding biology of the Chilean Mockingbird (Mimus thenca) in central Chile

Abstract

The biology of the species was studied in the locality of San Manuel, Melipilla in central Chile. The Mockingbird breeding season extended from late September through late December with a peak in October. Nests are constructed at an average height of 1.64 m. The nests were a typically cup-shaped nest, built with thorny sticks and lined with soft vegetable wool, the internal diameter averaged 107 mm. The nests were always in well hidden locations and this species at the study site demonstrated a preference for thorny shrubs with thick foliage. Clutch size normally consists of three eggs, but varied from two to four eggs, with 47% of the eggs being subelliptical in shape. The base color of the eggs were blue and showed a large variability of markings from wreathed, capped, spotted, and overlaid, and they were splashed, or blotched with reddish brown marks. Incubation period was between 14 - 16 days, on average 14.8 days and the nestlings fledged between 11 -12 days of age, the T10-90 period was 8.5 days and the growth constant was K= 0.517. Mean body mass at hatching was 5.7 g with the maximum mass reached by any nestling on the nest was 64.7 g. The observed diet consisted of a variety of insects and fruits. Mortality (95%) occurred at the egg stage, many of those eggs were punctured or stolen by Shiny Cowbirds (Molothrus bonariensis). On the observed nests of Chilean Mockingbird, 53% contained Shiny Cowbirds eggs. The total reproductive success was 30%.