Reference: Saalfeld, S.T., McEwen D.C., Kesler D.C., Butler M.G., Cunningham J.A., Doll A.C., English W.B., Gerik D.E., Grond K., Herzog P., Hill B.L., Lagassé B.J., Lanctot R.B. (2019). Phenological mismatch in Arctic-breeding shorebirds: Impact of snowmelt and unpredictable weather conditions on food availability and chick growth. Ecology and Evolution, 9(11), 6693-6707. https://doi.org/10.1002/ece3.5248
Where’s my food?
Predator and prey relationships dominate the natural world. When predators can no longer rely on prey for nourishment, stresses easily arise that diminish or even eliminate whole species, including the ones humans rely on for food, clothing, pest management, and other everyday needs.
What do we know? We know climate change is disrupting the delicate balance between predator and prey relationships, especially in the Arctic, a region heavily affected by climate change. Arctic shorebirds who breed in this region rely on a short, yet usually predictable, invertebrate supply as nourishment for their young. Climate conditions dictate the activity of these invertebrates and researchers are starting to suspect that climate change will impact seasonal food availability for shorebird populations.
Several studies have already noted that both Arctic shorebirds and their invertebrate prey are undergoing a phenological, or timing, mismatch between when shore birds hatch and when their invertebrate food supply is abundant. There are many examples of phenological mismatches occurring in the environment. The one between bumblebees and nectar availability was covered in a previous Envirobites piece by Pernilla Borgstrom.
Sarah Saalfeld and her colleagues designed a multi-year experiment in Utqiaġvik (formally Barrow), Alaska to determine the degree and impact of phenological mismatch on traits related to shorebird hatching, survival, and growth. This work is one of the first to look at chick survival and growth in addition to time of hatching in relation to peak availability of their food source.
Bird (and insect) watching
The group collected data on shorebird (Dunlin, Pectoral Sandpiper, and Red Phalarope species) hatch dates, prey availability, and environmental variables yearly from 2010 to 2016. They also tagged chicks after hatching and measured their growth from years 2013 and 2016. Saalfeld and her colleagues defined the degree of phenological mismatch as the number of days between peak insect emergence and peak shorebird hatch. If the timing of these events matched, they would occur at the same time – any deviation and there is a mismatch!
They then used mathematical models to determine relationships between the degree of phenological mismatch and factors including timing of snowmelt, food availability for new chicks, and chick growth. They also compared food availability each season with the variables of hatch date and timing of snowmelt.
Consistency gives way to variability
When observing the prey, they saw a huge variability in prey emergence and activity among years.
It was clear that the prey was adapting to a changing climate.
On an annual scale, they saw a larger biomass, or total amount of organisms in a given area, during years with an early snowmelt while on a day to day scale, they observed more insect activity on days with higher temperatures and lower wind speeds. Because this daily variability made it difficult to observe trends, the researchers failed to identify an impact of phenological mismatch on either food availability or chick growth.
All was not lost however. The team found a very clear trend suggesting that arctic shorebirds experience increased phenological mismatch under earlier snowmelt conditions, an increasingly common occurrence. Namely, shorebirds tended to hatch too late in years the snow melted earlier than usual – the peak prey availability was already gone. Years in which the snow melted later than usual, the shorebirds hatched too early, before peak prey emergence occurred. There was a clear winner however and it appears that the early bird gets the worm. Early hatchlings, whether the snow melted early or late, always had access to more food, a trait even more important in early snowmelt years.
Climate is changing, both predator and prey race to adapt
Overall, the researchers saw that the prey was adapting to changing snowmelt while the predator was not. While it would be desirable for shorebirds to lay eggs earlier in the season to match insect emergence, other factors hinder how quick they can catch up. Factors that are difficult to change, such as migration cues and breeding ground preparation, make it almost impossible for birds to alter how soon they lay eggs.
While the egg laying patterns of Arctic shorebirds remain consistent, the young birds are experiencing highly variable food availability as a result of prey adapting its activity to variable climate and weather conditions. If climate change continuously causes earlier snowmelt, pressure to lay eggs earlier and earlier will likely increase although it is yet unknown whether shorebirds will be able to adapt fast enough.
Further studies, including those on older chicks and adult populations outside of breeding season, are needed to more clearly understand how chick survival rates relate to food availability and ultimately, weather patterns. Only with a comprehensive analysis of climate and shorebird survival will scientists be able to predict the effect of climate change on shorebird survival and other species that affect human livelihood.