Breeding biology and natural history of the Great Shrike-tyrant (Agriornis lividus) in central Chile

Abstract

The breeding biology of the Great Shrike-tyrant (Agriornis lividus) was mainly studied on private land in central Chile. Its main habitat is coastal arid to semi-arid hills in areas mainly with thorny bushes, cacti plants and with preference in areas with terrestrial bromeliads like Puya sp. Mostly below 1.700 m, but locally it can reach up to 2.600 m. Its breeding season extended from early September to late October with one brood per season and if eggs were lost there seems to be no replacement. The nest is typically cup shaped nest, a very bulky structure built with thick sticks, a mid-thick layer of mosses and lining was made either with only mosses or with soft vegetable items and sometimes added some mammalian hair depending on availability, e.g., horse or rabbit fur, and very rarely feathers of other bird species. Nest placement ranged between 1.5 to 2.5 m from the ground level. There was a tendency to prefer thorny plants mainly terrestrial bromeliad Puya chilensis, and sometimes a cactus Echinopsis chiloensis, for nest placement. Clutch size was from two to five eggs, but primarily three eggs (47%) or four (41.2%) (n=17) and most eggs (42%) (n= 50) were sub elliptical in shape. The eggs had as base color a matt to semi-glossy very pale brown or creamy brown with a large variability on the markings, ranging from almost no marks to a several irregular dots or blotches, very dark brown to reddish brown in coloration, sometimes forming a wreathed pattern. It was noted that only the female incubates. The average incubation period was 20 days (19–21) and the nestlings departed from the nest between 18–20 days. The nestlings were brooded full time until age 7-8 days and partially until 15 days of age. The T_10–90 period was 13 days, and the growth constant was K = 0.338. On average, the body mass of nestlings at hatching was 5.9 g, and the maximum acquired was 84.5 g at 18 days of age. The observed nestling diet was 82% between lizards and caterpillars. The adults brought to the nest ground-dwelling prey items (70,4%) and the rest were mainly arboreal but some aerial prey. Post-breeding adults also feed mostly on ground dwelling creatures and arboreal prey items, but also included some fruits like Calafate (Berberis microphylla) and Maitén (Maytenus boaria). Most mortality 32.5% occurred at the egg stage. The total reproductive success was 53.4%. It is a partial austral migrant with some years part of the population stay to breed. Late March early April is when large numbers have been detected moving north through the area.