Migratory birds have new strategy to cope with climate change

As the world grapples with the consequences of climate change, a new study reveals that the deteriorating habitat conditions have significantly disrupted the timing of bird migration. 

However, birds have found a way to partially compensate for this disruption by delaying their spring migration and completing the journey faster, although this strategy comes with a cost – a decline in overall survival.

The groundbreaking study was conducted by researchers from Cornell University, the University of Maryland, and Georgetown University, and their findings were published in the journal Ecology. The team focused on the American Redstart, a migratory songbird that breeds in North America and winters in the Caribbean.

“We found that our study species, the American Redstart, can migrate up to 43% faster to reach its breeding grounds after delaying departure from wintering grounds in Jamaica by as much as 10 days,” said study lead author Bryant Dossman.

Dossman, who led the study while a graduate student at Cornell and is currently a postdoctoral fellow at Georgetown, added that “increased migration speed also led to a drop of more than 6% in their overall survival rate.”

The tactics employed by these birds to speed up their migration include flying faster and making fewer or shorter stopovers to refuel along the way. However, migrating faster only helps to compensate for the delayed departure to a certain extent, as it cannot entirely make up for the lost time. 

For instance, Dossman explains that for a 10-day delay, individual birds can recover about 60% of the lost time, but they still arrive late on the breeding grounds.

Jamaica has experienced increased aridity in recent decades, leading to a decline in insect populations, which form the primary diet of the American Redstart. This shortage of insects means that the birds now take longer to get into condition for the rigors of migration, especially those in poorer quality habitats. 

Simultaneously, climate change has caused plants to green and insects to emerge sooner on the breeding grounds.

Dossman emphasizes the importance of keeping to a tight schedule for migratory songbirds, as they generally only live for a year or two, giving them only one or two chances to breed.

In contrast, longer-lived birds are less likely to take the risk of speeding up migrations, as they have more opportunities throughout their lives to breed and pass on their genes.

Good news and bad news for migrating birds

To conduct the study, researchers employed a combination of historical data, automated radio tracking, and light-level tags. By comparing the redstarts’ expected departure dates with their actual departure dates in recent years, scientists were able to determine how the birds’ migration patterns have changed over time. The findings suggest that the subtle effects of climate change on animal behavior can be challenging to detect without long-term observation.

“The behavioral shifts documented in this research remind us that the manner in which climate change affects animals can be subtle and, in some cases, able to be detected only after long term study,” commented study co-author Professor Amanda Rodewald.

The study also highlights the importance of understanding how animals might compensate for the challenges imposed by climate change. 

“Understanding how animals can compensate is an important part of understanding where the impacts of climate change will play out,” said study co-author Peter Marra. “In this case, we may not lose a species entirely, but it is possible that populations of some species may go extinct locally due to climate change.”

Interestingly, the researchers found that the changes observed in the redstart’s wintering grounds can carry over into the breeding season. While the overall redstart population remains stable and is increasing across much of its breeding range, detailed eBird Trend maps reveal that the species is declining in the northeastern United States and southern Quebec, Canada.

Dossman shared some optimism regarding the birds’ ability to adapt to environmental changes: “The good news is that birds are able to respond to changes in their environment. They have some flexibility and variation in their behaviors to begin with, but the question is, have they reached the limit of their ability to respond to climate change?”

The research sheds light on the challenges faced by migratory birds due to climate change and the adaptations they have developed to cope with these changes. However, the long-term consequences of these adaptations on their overall survival and breeding success remain uncertain.

As climate change continues to reshape our planet, understanding how animals respond and adapt is crucial for the conservation and management of ecosystems. This long-term study of the American Redstart serves as a valuable case study in comprehending the subtle ways in which wildlife might be affected by our changing climate, and it underscores the need for more comprehensive, long-term research on various species.

More about migratory birds

Migratory birds exhibit a range of behaviors as they undertake their seasonal journeys between breeding and non-breeding grounds. These behaviors can be broadly categorized as follows:

1. Navigation and orientation: Migratory birds have an innate ability to navigate vast distances using a combination of environmental cues and their internal compass. They rely on the sun, stars, Earth’s magnetic field, and various other landmarks to find their way.
2. Timing: Many migratory bird species follow a strict annual schedule, with their departure and arrival times closely linked to seasonal changes in daylight and temperature. This ensures they arrive at their breeding grounds when conditions are optimal for reproduction and food availability.
3. Flight behavior: During migration, birds display different flight behaviors depending on their size, morphology, and environmental conditions. Some species, such as waterfowl and shorebirds, undertake non-stop flights over long distances, while others, such as songbirds, fly in stages, stopping to rest and refuel at regular intervals.
4. Flocking: Many migratory bird species, particularly those that travel in large groups or flocks, exhibit coordinated flight behaviors. This social structure provides numerous benefits, such as improved navigation, protection from predators, and reduced energy expenditure through aerodynamic advantages.
5. Stopover behavior: Migratory birds often utilize stopover sites to rest, feed, and refuel during their journeys. They exhibit specific behaviors at these sites, such as foraging, roosting, and interacting with other individuals.

Common migratory bird species

Some of the most common species of migratory birds include:

1. Arctic Tern: This small seabird undertakes the longest known migration, traveling around 25,000 miles (40,000 km) annually between its Arctic breeding grounds and Antarctic non-breeding grounds.
2. Bar-tailed Godwit: This large shorebird is known for its impressive non-stop flights, covering up to 7,000 miles (11,000 km) between Alaska and New Zealand in about nine days.
3. Swainson’s Hawk: This bird of prey migrates from North America to Argentina, traveling around 6,000 miles (9,600 km) each way.
4. Ruby-throated Hummingbird: This tiny bird migrates between North and Central America, covering up to 3,000 miles (4,800 km) round trip, with some individuals making an 18-hour non-stop flight across the Gulf of Mexico.
5. Barn Swallow: A widespread migratory species, the Barn Swallow breeds across the Northern Hemisphere and migrates to Central and South America, southern Africa, and parts of Asia for the non-breeding season.

These are just a few examples of the thousands of migratory bird species found worldwide. Their incredible journeys and unique behaviors highlight the complexity and resilience of the natural world.

Research funding was provided by the Cornell Lab of Ornithology, the Smithsonian Institute, and the National Science Foundation.

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