Breeding phenology and estimates of reproductive outcomes in Falkland SteamerDucks ( Tachyeres brachypterus )

Breeding success in birds reflects a balance between parental strategies and environmental conditions, yet it remains poorly documented for many island endemics. We describe the breeding phenology and reproductive performance of the Falkland SteamerDuck (Tachyeres brachypterus), the only waterfowl species endemic to the Falkland Islands. From September 2023 to February 2024, we monitored territorial pairs at Bleaker Island, an offshore island with restored habitats, and Stanley Harbour, adjacent to the Falkland Islands’ capital. Territorial pairs were most often found on pebble beaches. Breeding outcomes and phenology were reconstructed from early breeding stages through fledging. We observed nests beginning in late October, downy chick rearing from November to late February, and fledged broods beginning in mid-January. In Stanley Harbour, clutch size was 4.3 ± 1.1 eggs [1–7] (mean ± SE; range; n = 6 nests), downy broods comprised 4.4 ± 0.3 ducklings [1–9] (n = 34 broods), and fledged broods 2.9 ± 0.4 ducklings [1–8] (n = 17 broods). On Bleaker Island, downy broods comprised 4.3 ± 0.2 ducklings [1–8] (n = 17 broods), and fledged broods 3.2 ± 0.3 ducklings [1–8] (n = 33 broods). Duckling survival was 58 ± 8% in Stanley Harbour and 78 ± 7% on Bleaker Island. Our estimates of breeding parameters for the Falkland SteamerDuck constitute a baseline for future studies of the breeding population. This baseline is key to understanding future population trends in the context of global changes.