How Shorebirds Adapt to a Warming Arctic

Shorebirds nest in Arctic Alaska to take advantage of the abundant food source of insects. As the timing of migration and timing of insect emergence gets farther apart (mismatched), birds may adjust by laying eggs sooner after they arrive.

Rock sandpiper/USFWS

Shorebirds migrate to the Arctic during spring to nest and raise young, taking advantage of plentiful invertebrate prey (bugs!) during the brief Arctic summer. Many of these shorebird species have declined because of habitat loss and hunting in distant overwintering areas and along migration routes. However, changes on their Arctic breeding grounds may play a part in the declines as well.

The timing of shorebird arrival in the Arctic has evolved to match the emergence of invertebrates, thereby best meeting nutritional needs for egg formation, incubation, and growth of chicks. Shorebirds generally initiate their migrations based on lengthening daylight in overwintering areas and adjust their rate of migration based on environmental conditions along migratory routes far from the Arctic. In contrast, Arctic invertebrates are not migratory and rely on local clues such as air temperature and snow melt for emergence.

The Earth is warming, but not uniformly; climate change is accelerated in polar regions, resulting in potential mismatches between arrival of shorebirds and availability of their prey. We studied the timing of invertebrate availability and nesting of shorebirds at 8 sites across the North American Arctic, from Nome and Cape Krusenstern National Monument in northwest Alaska to Nunavut, Canada. Average annual temperatures in this region increased by 2 - 3 degrees C since the mid-20^th century, with the greatest warming during winter. Our data suggest that invertebrates are emerging an average of 1 - 2.5 days earlier per decade over this same period.

Some shorebirds have responded by arriving earlier on Arctic breeding grounds, but this varies by species. Those species arriving late to a warming Arctic may adjust by initiating egg-laying sooner once they arrive, but the ability to adapt in this manner is limited. We believe that mismatches between shorebird arrival, nesting, and invertebrate availability may be at least partially offset by warming-induced prolongation of invertebrate availability and lower energetic requirements for chicks to maintain body temperature. If current climatic trends continue, however, we predict that some species of shorebirds will be unable to meet energetic needs for successful reproduction and chick survival will decline.

Predictors of invertebrate biomass and rate of advancement of invertebrate phenology across eight sites in the North American Arctic

Abstract

Average annual temperatures in the Arctic increased by 2-3 °C during the second half of the twentieth century. Because shorebirds initiate northward migration to Arctic nesting sites based on cues at distant wintering grounds, climate-driven changes in the phenology of Arctic invertebrates may lead to a mismatch between the nutritional demands of shorebirds and the invertebrate prey essential for egg formation and subsequent chick survival. To explore the environmental drivers affecting invertebrate availability, we modeled the biomass of invertebrates captured in modified Malaise-pitfall traps over three summers at eight Arctic Shorebird Demographics Network sites as a function of accumulated degree-days and other weather variables. To assess climate-driven changes in invertebrate phenology, we used data from the nearest long-term weather stations to hindcast invertebrate availability over 63 summers, 1950–2012. Our results confirmed the importance of both accumulated and daily temperatures as predictors of invertebrate availability while also showing that wind speed negatively affected invertebrate availability at the majority of sites. Additionally, our results suggest that seasonal prey availability for Arctic shorebirds is occurring earlier and that the potential for trophic mismatch is greatest at the northernmost sites, where hindcast invertebrate phenology advanced by approximately 1-2.5 days per decade. Phenological mismatch could have long-term population-level effects on shorebird species that are unable to adjust their breeding schedules to the increasingly earlier invertebrate phenologies.

Shaftel, R., D. J. Rinella, E. Kwon, S. C. Brown, H. R. Gates, S. Kendall, D. B. Lank, J. R. Liebezeit, D. C. Payer, J. Rausch, S. T. Saalfeld, B. K. Sandercock, P. A. Smith, D. H. Ward, and R. B. Lanctot. 2021. Predictors of invertebrate biomass and rate of advancement of invertebrate phenology across eight sites in the North American Arctic. Polar Biology 44: 237-257.