Climate change effects on migratory birds

Flyways

Climate change is not uniform globally or within the United States. Therefore, migratory birds’ arrival varies each spring and they are prompted to move within their four main flyways by specific weather and temperature patterns.

According to NASA, in the western half of the U.S., bird migration is strongly linked with regional air and ocean surface temperatures of the adjacent Pacific Ocean. Above-average temperatures are causing birds to migrate earlier in the spring.

In the eastern half of the U.S., however, migration is linked with Rossby Waves, airwaves flowing east to west that transfer warm air from the tropics poleward and cold polar air to the lower latitudes. They form due to the Earth’s rotation and geography and significantly impact weather and climate patterns for thousands of miles.

In addition to these cues, birds rely on the annual change in day length on migration timing. Knowing the causes of bird migration patterns allows us to manage and direct our efforts to protect, restore, and preserve their habitat, especially in the flyways.

Migration

Birds migrate short or long distances based on food availability and climate conditions correlating with their annual life cycles. A longer migration distance increases the risk to survival. Since so many factors affect breeding and migration, birds must be extremely adaptable and flexible to shifts in global climate patterns that are not equal across geographic regions.

In Minnesota’s temperate zone, increasing winter and spring temperatures could promote birds staying through the winter and breeding earlier.

Based on historical records, current populations of migratory birds are shown to arrive earlier in the spring and breed sooner than they did in the past, but these trends are not equal across species. The estimated rate of change varies based on several factors, including the availability of good quality food, the amount of daylight, how far birds migrate, the specific species, life-history traits, and geographic region.

Life cycle

Migratory birds use different areas at different stages of their annual cycle and with varying degrees of climate across space and time. The effects of factors in one stage can cascade to the next stage, which raises the concern of adaptability to environmental changes encountered during critical stages in the cycle.

Breeding ranges have been extending to the north in Minnesota, which leads to more indications of shortening, rather than lengthening migratory routes.

However, geographical barriers (e.g. mountains, large lakes, etc.) may prevent this gradual range shift and leave some migratory species with a more complex and longer route.

This longer distance paired with molting time can delay the remaining life cycle stages. The arrival date on the breeding grounds and the quality of breeding habitat is key to finding a mate and raising a successful brood.

Successful breeding relies on the peak of food availability during the high energy-demanding breeding period. Food availability depends on the spring temperatures and precipitation. Warmer spring and fall temperatures along with insect availability allow birds to advance their laying date, molt, and depart later in the fall for wintering areas.

A shift in wintering territories, if they are high quality, may enable migratory birds to grow healthier plumage and, again, arrive on the breeding territory the following spring in prime condition.

Responses

Increasing winter temperatures and precipitation affect the number and proportion of migratory species.

• Future predictions propose that a 1°C increase in the coldest month temperature will cause a decline in the number and proportion of migratory species.
• A 1°C increase in spring temperatures is likely to cause migratory species numbers and proportions to increase.
• On the other hand, precipitation increased by 1 mm is proposed to increase the number of species but decrease the proportion of species, mostly due to a decline in migratory activity.

Migratory activity is expected to decline. as species adapt to the changing climate. Fewer migratory activities may be caused by higher survival rates of non-migratory, resident species during mild winters, and increasing population densities.

As the resident species’ population increases, migratory species will have more competition for food, breeding territories, and nest sites. However, resident species populations will grow with increased reproductive success due to favorable climatic conditions and may evolve from a non-migratory into a migratory population resulting in a range shift.

Climate change will modify species richness and avian community compositions.

Habitat considerations

The most crucial goal for land stewards is to encourage large, genetically diverse bird populations through conservation planning that identifies land and species priorities and monitors the effectiveness of those management strategies. It is key to protect areas that may be used during future shifts in migratory bird range, both seasonally and year-round. 

As the major threat facing migratory birds is land-use change, providing low-intensity land use and natural or semi-natural land will help conserve migratory species long-term.

The effects of climate change on wetlands are predicted to be most severe due to the increased demand for domestic, industrial, and agricultural use with an exponentially growing human population and rising temperatures, all of which lower water table levels.

Human activities along with climate change are resulting in a decline of diverse forest systems, which is linked to bird population declines. A decrease in feeding habitat for birds affects more individuals of a greater number of species over a longer period.

Preserving floodplain catchments, restoring shorelines, managing water and air quality, preventing deforestation, and reducing soil erosion are all significant conservation strategies in managing land for migratory birds.

Even with conservation land management and stewardship, evolutionary change and adaptive response vary among bird species. Overall, species now spend over 10% more time on non-breeding grounds than breeding grounds.

Species with longer migration distances traveling further north spend even less time on those breeding grounds. This is a consequence of northern breeding grounds experiencing the strongest warming events.

In addition, the length of time birds spend at sites in their flyways during migration is typically less than 2% of their annual cycle. Species with shorter migration distances have an increasing tendency to be more broadly distributed.

Based on low, steady, or high emission scenarios a broad range of future outcomes is possible concerning migratory birds. Many habitat considerations can be implemented in Minnesota on various scales for a wide range of migratory bird species. With more than 70% of land in Minnesota being privately owned, being a land steward is critical for the future.

The University of Minnesota is developing tools to help forecast climate change and suggest strategies for adaptation.

• Minnesota ForCAST Tool: evaluate how a changing climate and changing markets might affect Minnesota’s forests and ecosystem services
• MN CliMAT - Minnesota Climate Mapping and Analysis Tool
• Creating climate-ready woodlands
• How to get a woodland stewardship plan