Temperatures are warming fastest at high latitudes and annual temperatures have increased by 2-3˚ C in the Arctic over the second half of the 20th century. Shorebirds respond to cues on their overwintering grounds to initiate long migrations to nesting sites throughout the Arctic. Climate-driven changes in snowmelt and temperature, which drive invertebrate emergence, may lead to a lack of synchrony between the timing of shorebird nesting and the availability of invertebrate prey essential for egg formation and subsequent chick survival. We modeled the biomass of invertebrates captured in modified Malaise traps as a function of accumulated temperature and weather variables for eight North American research camps in the Arctic Shorebird Demographic Network over the years 2010-2012. Models were based on data from the closest weather station and used to hindcast invertebrate biomass for the last ~60 years. From the hindcasted invertebrate data we calculated three measures of invertebrate phenology: the first day with invertebrate biomass above 10 mg; the number of days in May, June, and July with invertebrate biomass above 10 mg; and the date of peak invertebrate biomass. The 10-mg threshold was based on literature indicating it provided sufficient daily prey biomass to support normal shorebird chick growth. Additionally, a sensitivity analysis using 5, 15, and 20 mg showed that our results were robust to variation in this threshold. Each response was regressed against year to investigate changes over time. Changes in hindcasted invertebrate phenology were most conspicuous at the northernmost camps and were on the order of 1 to 3 days per decade. At Barrow, Ikpikpuk, and MacKenzie Delta, the timing of the first day with invertebrate biomass above 10 mg has advanced by 2 to 2.5 days per decade. At Barrow and Ikpikpuk, the number of days with invertebrate biomass above 10 mg has increased by 1.5 to 2 days per decade. The timing of peak invertebrate biomass has advanced at Ikpikpuk and Cape Krusenstern by 1 to 1.5 days per decade. Although our results suggest that seasonal prey availability for arctic shorebirds is advancing, the potential for trophic mismatch is most likely at the northernmost sites we evaluated, although it may be mitigated by similar advances in shorebird migration and nesting as reported from other Arctic sites.
