Between 26 and 28 June 2021, the United States' Pacific Northwest endured an unprecedented heatwave that broke previous temperature records by 5 °C. Here, we report the impacts of the heatwave on Bushtit (Psaltriparus minimus) nests being monitored as part of a long-term study in Portland, Oregon. Of the 8 nests active during the event, nestling mortality was 100% in 3 nests and 4 broods survived at least in part. We suspect the excessive heat forced at least one additional brood to fledge early. Remains of nestlings found in 2 nests that eventually fledged suggest that even those encountered brood reduction during the heatwave. Nests with broods that survived were closer to a water source (x̄=13 m) than nests with broods that did not survive (x̄ = 148 m). In addition, surviving broods were younger (either eggs or <4 d of age) than those that perished (>9 d of age). Since these are only the second incidence of total nestling mortality other than depredation observed during Sloane's long-term research on Bushtits in Oregon and Arizona (1986–present), we consider this to be a significant finding and indicative of the future negative effects of global climate change on temperate zone species of breeding passerines.