Climate Change Response: Bird Migrations
Matt Pawlush
Annual bird migrations, butterfly migrations and the sprouting/flowering of plants all fall under the category of phenological events. Phenology is the study of information related to the timing of seasonal events. Many of these seasonal events depend on climatic and environmental factors such as light availability and temperature. Phenological response is when seasonal events happen earlier or later than usual, due to, for example, temperatures that are higher or lower than normal throughout the year. Thus, if the past year had been particularly warm, a bird might migrate from its wintering ground early. Phenological events of species often coincide, so if one is thrown off it could negatively impact other species. This has potential to hurt multiple species’ ability to thrive and could have repercussions throughout the ecosystem. It’s important to keep track of these phenological data so researchers can visualize which areas and organisms are most impacted by climate change and determine environmental and climatic changes whose adverse effects may be difficult to detect over short periods of time such as increasing mean annual temperature (MAT).
With no slowing to global warming in sight, all organisms will have to respond to this change. Generally, animal populations have three options to deal with increases in temperature: physiologically adjust to new thermal regimes, change distribution patterns, or, at worst, face local extinction."
Bird migrations are annual population-wide events that vary in time and distance traveled for each species. These migrations are highly dependent upon MAT because it impacts both departure and arrival times at their breeding and wintering grounds. With the effects of climate change becoming increasingly apparent, the MAT for many breeding and wintering grounds has increased in recent years, prompting some bird populations to alter their migration patterns. Zaifman et al. 2017 looked at how MAT impacts migration in different US states from 2010-2016. Two states that have seen rapidly increasing MAT are Alaska and Maine (Alaska’s MAT has increased ~1.7 ºC in the past 60 years, and Maine’s MAT has increased the same amount of the last century). South Carolina was selected as a control because it has experienced more stable and slower increasing MAT (only a ~.56 ºC increase since 1974).
In each study area, around one third of the bird species had alterations in the timing of migration. Both short and long-distance migrating species in South Carolina spent less time in their wintering grounds which is thought to be related to increasing MAT, where warmer temperatures result in greater food availability. Birds that traditionally migrate to wintering grounds for more food resources would not be pressed to migrate as soon because food has become increasingly available in their breeding grounds for longer periods of time. This is important because some ecosystems may depend on migrating bird species as an important predator or prey species, and a shift in that timing could have adverse effects on the ecosystem. Of 97 species analyzed in Alaska, 31 showed changes in migration patterns in response to increasing MAT. The bufflehead (a species of duck) saw the most extreme change of any bird in Alaska, arriving later and departing earlier over time. The late arrival and early departure is a trend that held for around 26% of species analyzed in Alaska. Of all the birds found in Maine, including the near-threatened semipalmated sandpiper, 31% of them stayed longer as temperatures increased. This species of sandpiper remained at its spring stopover longer when experiencing a higher minimum seasonal temperature which means it spent less time at its breeding and wintering grounds at which it may hold an important ecological role.
Around a third of the bird species in the study are showing a phenological response to climate change, meaning that some birds are responding behaviorally to climate change and others are not. Intuitively, it might seem that a phenological response by the species to increasing MAT will be best for its survival, but it’ll take more observation and study to see if that’s the case. With increasing MAT scientists will need to closely observe species and determine if they do or do not respond phenologically to the changing climate as to not lose important members of our many different ecosystems.
Sources
Walther, G. R., Post, E., Convey, P., Menzel, A., Parmesan, C., Beebee, T. J., ... & Bairlein, F. (2002). Ecological responses to recent climate change. Nature, 416(6879), 389.
Zaifman, J., Shan, D., Ay, A., & Jimenez, A. G. (2017). Shifts in Bird Migration Timing in North American Long-Distance and Short-Distance Migrants Are Associated with Climate Change. International Journal of Zoology, 2017.