With fall’s cool air upon us, and the shorter days following the Autumn equinox on September 22nd, migration has been set into motion. Migration is the cyclical phenomenon where animals move over large distances, driven by environmental changes such as length of day and temperature. 

Meet the Ruby-throated Hummingbird

Ruby-throated hummingbirds are our resident hummingbird species in the Great Lakes region, and throughout the Eastern United States. They are metallic green, with males sporting the namesake bright ruby throat. Adults measure only 3 to 4 inches long, and weigh 2-6 grams - that is less than a quarter! Ruby-throated hummingbirds breed in the forests and fields of eastern North America during spring and summer, and migrate south to tropical forests and scrublands to spend the fall and winter. 

Hummingbirds rely on nectar from flowering plants as their primary food source, and this develops a close relationship between the animal and the plant. Hovering, or the ultra-fast flying they are capable of, is an essential feeding behavior that is very energetically expensive to maintain, which is why it is so important that hummingbirds have adequate food sources to fuel themselves. Hummingbirds need to eat 5-6 times per hour to fuel their fast metabolism.

Threats to Hummingbirds 

Flower Blooming Periods

Imagine that you show up to your favorite restaurant just as they close the kitchen - even though the internet said they would be open and you have been there dozens of times before at that exact time - this is how a hummingbird feels. 

Plants are blooming at earlier times each year because of changing climate trends, causing concern that hummingbird arrival may become mismatched with the blooms they depend on so heavily. This is especially pronounced at higher latitudes, or closer to the poles, and could even create limits to migration and contract ranges if nesting success is impacted. 

This matters because hummingbirds also have important jobs in ecosystems. Because hummingbirds get the other non-nectar portion of their diet from insects, they play a role in balancing pest populations. Humans also depend on pollinators, like hummingbirds, to pollinate our food crops! 

Hummingbird Adaptations

To combat the impacts of a changing world, some animals move physical locations to go somewhere else more suitable. Higher altitudes typically have lower temperatures, so moving up in elevation can counteract localized warming, but this is not a catch-all solution. Scientists with the National Science Foundation reported that hummingbirds that relocated to high altitudes had a significant decrease in metabolic rate, suggesting that low air pressure and oxygen availability reduces hovering performance in Anna’s hummingbirds, and even pushes them into nightly hibernation. Facing these physiological challenges only becomes more costly for low-elevation hummingbirds that are driven to find new food sources. 

Another study from The Auk assessed the migration of ruby-throated hummingbirds and found that the birds are moving roughly 2 weeks earlier than historical records show. The scientists found correlation between earlier arrivals to breeding grounds, and warmer winter and spring temperatures in North America, which is a trend that experts expect to continue. If they continue to leave early, they will arrive at different times than the flowers they feed on. 

How can I help hummingbirds?

Scientists are still learning how hummingbirds are adapting, but there are lots of ways you can support these important pollinators amidst the challenges they are facing. The best place to start is your backyard. You can… 

• Record data for community science projects like BudBurst to share flowering plant data with scientists
• Plant native flowering plants, like those found in this guide from the US Department of Agriculture suggests
• Supplement nectar resources in your backyard with birdfeeders that are monitored/cleaned regularly

Next time you see a hummingbird, consider the distance it’s travelled for you to see it, and the amazing life that supported that journey! 


Sources

Courter, Jason R., et al. “Assessing migration of ruby-throated hummingbirds (Archilochus colubris) at broad spatial and temporal scales.” The Auk, vol. 130, no. 1, Jan. 2013, pp. 107–117, https://doi.org/10.1525/auk.2012.12058.

McKinney, Amy M., et al. “Asynchronous changes in phenology of migrating broad‐tailed hummingbirds and their early‐season nectar resources.” Ecology, vol. 93, no. 9, Sept. 2012, pp. 1987–1993, https://doi.org/10.1890/12-0255.1.

Spence, Austin R., et al. “Anna’s hummingbird (Calypte anna) physiological response to novel thermal and hypoxic conditions at high elevations.” Journal of Experimental Biology, vol. 225, no. 10, 15 May 2022, https://doi.org/10.1242/jeb.243294.
Austin R. Spence, Hannah LeWinter, Morgan W. Tingley; Anna's hummingbird (Calypte anna) physiological response to novel thermal and hypoxic conditions at high elevations. J Exp Biol 15 May 2022; 225 (10): jeb243294. 
McKinney, A.M., CaraDonna, P.J., Inouye, D.W., Barr, B., Bertelsen, C.D. and Waser, N.M. (2012), Asynchronous changes in phenology of migrating Broad-tailed Hummingbirds and their early-season nectar resources. Ecology, 93: 1987-1993. 
Courter, J.R., Johnson, R.J., Bridges, W.C., Hubbard, K.G., "Assessing Migration of Ruby-Throated Hummingbirds (Archilochus colubris) at Broad Spatial and Temporal Scales," The Auk, 130(1), 107-117, (1 January 2013) 
University of Maine Ruby-Throated Hummingbird Fact Sheet

https://www.allaboutbirds.org/guide/Ruby-throated_Hummingbird/lifehistory

This effect is pronounced at lower latitiudes (below 41 degrees?). 

Warmer winter and spring temperatures in North American breeding grounds were correlated with earlier arrivals at lower latitudes in our recent period.

USDA Eastern US Hummingbird Flyer