Breeding biology of the Bornean Stubtail (Urosphena whiteheadi) onMount Kinabalu, Sabah, Malaysia

Life-history traits have been described disproportionately for temperate-breeding birds. Efforts to conserve global biodiversity require a more holistic understanding of avian life-history theory across biomes and geographic locations. In this account, we present the first detailed description of the breeding biology of the Bornean Stubtail (Urosphena whiteheadi). We discuss the stubtail's breeding strategies in the context of life-history theory and contrast them with those of 4 other members of the same family breeding at higher latitudes and lower elevations. The Bornean Stubtail is a tropical montane passerine belonging to the Old World Cettiidae family and endemic to the island of Borneo. Compared to other Cettiidae warblers, the Bornean Stubtail has a small clutch of 2 eggs and a long incubation period of 23.0 +/- 0.10 d. At our site, their open-cup nests were constructed of moss and placed on or near the ground on vertical features in rainforest understory. The nests experienced a daily survival rate of 0.939 +/- 0.006 and daily predation rate of 0.054 +/- 0.006. Mean fresh egg mass was 1.87 +/- 0.012 g. Egg-laying began in mid-February and continued into May. The number of active nests increased until mid-March at which point it remained relatively consistent until mid-May when it began to taper off. Nest attentiveness during incubation was low with a very long off-bout of similar to 7 h every day that decreased to similar to 4 h later in incubation, explaining the species' long incubation period. In contrast, nestling provisioning rates increased steadily over the nestling period (mean 12.53 +/- 0.24). Nestling growth followed a logistic trend commonly seen in passerines, and near-adult sizes were reached by fledging.