| Summary: | Shifts in phenology are among the key responses of organisms to climate change. When rates of phenological change differ between interacting species they may result in phenological asynchrony. Studies have found conflicting patterns concerning the direction and magnitude of changes in synchrony, which have been attributed to biological factors. A hitherto overlooked additional explanation is differences in the currency used to quantify resource phenology, such as abundance and biomass. Studying an insectivorous bird, Sanderling, and its prey, we show that the median date of cumulative arthropod biomass occurred, on average, 6.9 days after the median date of cumulative arthropod abundance. In some years this difference could be as large as 21 days. For 23 years, hatch dates of Sanderlings became less synchronized with the median date of arthropod abundance, but more synchronized with the median date of arthropod biomass. The currency-specific trends can be explained by our finding that mean biomass per arthropod specimen increased with date. Using a conceptual simulation, we show that estimated rates of phenological change for abundance and biomass can differ depending on temporal shifts in the size distribution of resources. We conclude that studies of trophic mismatch based on different currencies for resource phenology can be incompatible with each other. This Dryad repository contains five R-scripts (i.e. script 0, I, II, II, and IV). Script 0 is automatically sourced in the other scripts and does not need to be run manually. Script IV is a standalone script that does not require input files. In contrast, scripts I, II, and III rely on six data files as input. Five of these input files (i.e. I, III, IV, V, and VI) are provided in this Dryad repository. One input file (II) is not provided in this Dryad repository due to conflicting licenses. This file can be downloaded for free from the Greenland Ecosystem Monitoring webpage at the following permanent location ...
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