| Summary: | Abstract Species have responded to recent climate change via pronounced, but often variable, shifts in seasonal timing (phenology). Can this variability be accounted for by comparing responses along an elevational gradient and among species differing in seasonal timing and traits? We resurveyed montane grasshopper communities along a 1300‐m elevational gradient to examine phenological responses to ~50 yr of climate warming. Phenological responses were elevation dependent, influenced by relative warming (which was more pronounced at higher elevations) and by substantial interannual variability in available growing degree‐days (GDDs). The total number of GDDs available for development within a season declines with elevation, and correspondingly high‐elevation populations required fewer GDDs to reach adulthood. Although phenological advancements were particularly pronounced at higher elevations, consistent with a greater magnitude of climate warming, species as a whole initiated and completed development earlier in warmer years. During warm years, phenological advances were most pronounced early in development, and the timing of adulthood tended to occur earlier (at a similar or greater accumulation of GDDs). Phenological advancement was also more pronounced in early season species, which exhibit developmental plasticity to capitalize on warming. Interactions with elevation were also strongest for the early season species. Our study shows the importance of incorporating developmental information to understand the environmental and organismal mechanisms that drive variable phenological responses and suggests that the phenological impacts of warming will be concentrated early in development, among early season species, and at high elevations. Considering these drivers of phenological variability can aid understanding and predicting climate‐induced changes to community and ecosystem structure.
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