Hail-induced nest mortality and possible fright molting of a passerine bird during the pre-incubation period

Abstract

Deaths at the nest caused by hailstorms are rarely reported in birds and are usually revealed based on ex post monitoring. As a result, it is often difficult to draw inferences on the behavioral responses of individuals to hailstorms. In this note, I report the death of a female Lesser Whitethroat (Sylvia curruca) at its nest during the laying stage during a severe hail event in Poland. I inspected the nest soon after the storm and found traces that allowed me to reconstruct the nesting female's behavior. This observation contributes to the infrequent documentation that hailstorms may have lethal effects on shrubland birds, considered to be relatively resistant to hail-related mortality. It also shows evidence of partial incubation (nest attendance before clutch completion) during an extreme weather event. Finally, the female Lesser Whitethroat of this report lost all of her rectrices and other feathers that were found intact and spread out in the nest. Although feather loss due to hail trauma cannot be ruled out, the most likely explanation was their ejection (known as fright molt), possibly triggered by hail-associated stress. Should this be confirmed, this would be the first case of fright molt associated with a hailstorm reported in wild birds. My report adds further insights into bird responses to increasingly extreme meteorological events.