Since our last update, we completed our 41st and 42nd field seasons in summers 2022 and 2023. During these seasons, Olivia Pletcher transitioned to take over much of the day-to-day operations, coordinating nest checks at different colonies, leaving Charles Brown to focus on observations of foraging birds and collecting data on colony sizes. A major paper appeared in 2022 reporting the degree to which individual cliff swallows tend to occupy colonies of roughly similar size over their lifetimes, an assumption that has been important to much of what we have done over the years.
The summer of 2022 was hot and dry, as had been several of the preceding years, and reproductive success was fairly low. However, 2023 was unlike any recent season: mild and wet. This led to very high reproductive success for almost all birds in all colonies, and most notably the weather was the apparent cause of more late-nesting than we have ever seen in western Nebraska. Dozens of colonies began nesting late after the main group of birds there finished. We typically see this at a few sites in most years, but the late-nesting this season was widespread. Late colonies are usually smaller than earlier colonies, and this held true to some degree in 2023; however, we had one late colony (still feeding babies in mid-August) that was about 1400 nests in size, large by any standard! We think that the mild and wet conditions led to large insect populations, and cliff swallows responded to the greater food abundance with higher reproductive success and more late nesting. We are measuring how selection on colony size fluctuates annually in response to environmental conditions, so having an "extreme" year like 2023 is great for the natural selection study.
Also during 2023, Charles began work on a book on cliff swallows, detailing the history of the project and summarizing many of the findings. It is being done in memoir format, showing how scientific thinking at the time influenced each part of the project, and how one result led to additional questions and more research.