It is believed that birds fly south for the winter. However, climate change has triggered a cascade of ecological events that could soon prove this old adage false.
Birds marvel at migration, and ecological factors like temperature influence when birds make their move.
A study published this month in Nature Climate Change revealed that climate change has caused a phenological shift influencing when birds migrate, therefore igniting an array of ecological issues. Phenology, or the study of seasonal natural phenomena like migration, explains the correlation between climate and bird migratory patterns.
The study found that “for birds that have a synchronized timing of migration with resource availability, the likelihood that trophic mismatches may generate a phenological response in migration timing increases with climate change.”
The bigger implications of this phenological shift are startling. Later migration means there is a higher chance of trophic mismatch, which means resources are unavailable to the birds upon arrival. If caterpillars, a main food source for birds, are unavailable when the birds arrive, then their survival is threatened.
Analyzing data collected over the past 24 years, the researchers have determined that bird migration dates advance as temperatures warm. Further, they have found a more significant change in the northern latitudes of the continental United States where temperatures are warming at a faster rate than in the South.
Researchers also found that a greater shift in migration timing is more noticeable in the spring because birds are returning home to breed.
According to the study, “changes in phenology may directly impact the population distributions and ultimately lead to expansion or extirpation [of migratory birds].”
Birds also prosper when pollinating and eating pests. However, this phenological shift affecting migration therefore affects pollination. With delayed pollination, crops cannot flourish, consequently hurting farmers’ harvests and influencing what consumers buy at the grocery store.
This issue is not unique to the United States. A similar study published in Ecological Indicators analyzed data collected over 57 years on 195 bird species from various European and Canadian bird observatories. The researchers found that spring migration had advanced one week in total over the decades studied.
Climate change is a global issue threatening the existence of plants and animals. As these studies show, bird migration plays a crucial ecological role, but the phenological shift occurring is only becoming greater as climate change advances. The National Oceanic and Atmospheric Administration documented 2019 as the 43rd consecutive year with temperatures above average globally.
With resources depleting as birds migrate later, it may be true that the early bird does get the worm.
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Reporting Index:
- “Phenology of nocturnal avian migration has shifted at the continental scale”
- “Phenology of the avian spring migratory passage in Europe and North America: Asymmetric advancement in time and increase in duration”
- https://www.noaa.gov/news/2019-was-2nd-hottest-year-on-record-for-earth-say-noaa-nasa
- https://www.globalcitizen.org/en/content/bird-migration-wrecked-by-climate-change/
Lauren Berryman 