Climate change is significantly impacting bird migration patterns worldwide, leading to earlier arrivals at breeding grounds, altered routes, and increased challenges during migration.
Studies indicate that many bird species are arriving at their breeding sites earlier in spring. For instance, research shows that for every one-degree Celsius increase in temperature, birds have advanced their arrival by about one day. This shift is particularly evident in regions experiencing rapid warming. However, while spring migration is clearly shifting, autumn movements are less predictable, leading to more varied changes in timing.
These changes can create mismatches between birds and their food sources. If birds arrive before or after these food peaks, it creates a phenological mismatch. One example is the Afro-Siberian Red Knot, a shorebird that breeds in the Arctic. As the Arctic warms, snow melts earlier and insects emerge sooner. But the Red Knot hasn’t adjusted its arrival time fast enough. Chicks born after the food peak face malnutrition and lower survival rates. This has already led to smaller body sizes and population declines.
In North America, over 300 species have shifted their winter ranges northward by an average of 40 miles in recent decades. Some birds are moving inland, seeking milder conditions away from coasts. In Europe, short-distance migrants are especially quick to adapt. Milder winters allow them to stay closer to their breeding areas or even skip migration altogether. Some species are establishing entirely new migration paths. Richard’s Pipits, for example, traditionally wintered in South Asia but are now increasingly found in Southern Europe. This shift might be due to changing climate suitability in Europe and environmental pressures in their original wintering grounds. But not all species can adapt. And new routes can lead to competition with resident birds for food and space.
Climate change also affects the availability of food sources. In the Gulf of Maine, puffins are having difficulty finding their major food sources of white hake and herring. As the sea warms, the fish are moving into deeper waters or further north, making it harder for puffins to catch a meal and feed their young. Adult puffins are compensating by feeding their young butterfish, but young puffins are unable to swallow these large fish and many are dying of starvation. Delayed breeding seasons, low birth rates, and poor chick survival are all affecting the reproductive ability of these birds.
Additionally, climate change can impact how migratory birds behave. Warmer temperatures can remove the threat of food scarcity, leading birds to shorten their routes or not flying back to their original habitat at all. This, in turn, can lead to conflicts over food between migratory birds and resident animals. While some migratory birds, such as the Arctic tern, have compensated for strong winds by expending more energy on their journeys, other species have succumbed to the pressures of human activity.
To support migratory birds, it's essential to protect and restore habitats along their migration routes, reduce light pollution, and mitigate climate change by reducing greenhouse gas emissions. International cooperation and conservation efforts are crucial to ensure the survival of these species.