We quantified aspects of the breeding biology of Whiskered Auklets (Aethia pygmaea) at Buldir Island, western Aleutian Islands, Alaska, from 1993 to 1998 to provide a better understanding of this poorly known species' ecological relationship to other auklets (Aethia spp.). Whiskered Auklets nest in rock crevices in a range of habitats including talus slopes, cliffs, and beaches. No physical characteristic of nesting crevices predicted breeding success. Hatching dates varied among years; mean hatching dates averaged 20 June ±6.8 days (range 16–27 June). Chicks remained in the nest for 39 ± 2 days, with mean annual fledging from 27 to 29 July. Eggs were 44.1 ± 1.6 mm in length and 31.1 ± 1.61 mm in breadth, and varied significantly in size among years. Chicks weighed 17.4 ± 2.4 g (15.6% of adult mass) within two days of hatching and gained 3.8 g day⁻¹ in mass and 3.2 mm day⁻¹ in wing length during the linear growth period. Chicks fledged at 101.3 ± 11.3 g (90.5% adult mass) after a prefledging mass recession of 8.9% of peak mass, and a wing length of 102.2 ± 4.3 mm (93.5% adult wing length). Mass increase during the linear growth period and fledging mass varied among years, but wing growth and fledging wing length did not. Parents provisioned chicks after nightfall with copepods (Neocalanus spp.) and euphausiids (Thysanoessa spp.); the proportion of food types varied significantly among years. Eighty-nine percent of chicks that hatched survived to fledge; most of those that did not had died of starvation. Low-intensity monitoring underestimated breeding success but provided useful comparative information. Whiskered Auklets exhibited a suite of unique characteristics that make them an ecological outlier among Aethia auklets.