Ah, migration – what a wondrous time of year. The seasons are changing, birds are moving, and scientists are science-ing, or rather researching. However, none of this research is worth it if it’s not accessible to everyone. Articles can be heady and full of jargon that is confusing unless you are very familiar with the field of study. The article I’m going to write about is called “The implications of mid-latitude climate extremes for North American migratory bird populations” by Sorte, Hochachka, Farnsworth, Dhondt and Sheldon (hence forth referred to as Sorte, et al.). Basically, the researchers of this article took a bunch of data from eBird over a five-year period, and analyzed it to look at effects of climate extremes at mid-latitudes (see map below) on migratory bird species. They looked at short-distance vs. long-distance migrants occurring over non-marine areas; and used eBird checklists that were complete and that used either stationary, traveling, or area sampling methods of bird observations. It should also be noted that they did not look at anomalies such as accidental species (birds that got lost while migrating) or species associated with primarily marine environments (seabirds).
In case you weren’t aware, extreme weather and weather events are expected to increase over time. So, buckle up, fellow humans, the weather is going to get weird and it could be problematic for our fellow creatures, specifically migrating birds. The results of this study showed that basically some longer-distance-migrating species experienced climate-related stress during spring migration (primarily the month of March in this study) and then had a low productivity during the summer months (AKA breeding season for most creatures in the Western Hemisphere in non-tropical areas). However, the species that had a shorter distance to migrate seemed to show some resilience and flexibility when it came to dealing with the stress of climate extremes because they could detect changes and adjust. Migration is cued by seasonal changes, so if the changes occur at atypical times and birds follow those cues, then it can be problematic when extremes occur.
Why are these climate extremes a problem for migratory birds? Well, for species that have a long distance to migrate, these birds are expecting the weather to be a certain way upon arrival, and are unlikely to be able to detect and adjust for seasonal climate extremes during migration. If it’s incredibly hot or cold or there’s an intense storm, that will take away precious energy resources typically used for breeding. This will result in getting allocated to feeding and/or protecting themselves, and keeping warm or cool when they normally would not have to.
While this study looks at a lot of data and presents interesting findings that are probable, I believe more research needs to be done. Since everyone and anyone can submit to eBird, there are varying skill levels and not all observations may be accurate. I think that perhaps if this study only contained checklists from well-known, experienced birders, scientists, and researchers, then the data may be more credible.