One of the changes with climate change is a shift in seasonality. Many regions of the world are seeing an earlier arrival of spring weather and subsequent earlier arrival of plant blooming and insect emergence.
The first emergence of leaves on trees, flowering plants, and greens is an important indicator for birds to start breeding. Especially for migratory birds, environmental cues such as the length of days are important triggers for birds to prepare for nesting.
With the shift towards an earlier spring, scientists are finding that birds are lagging behind in responding to the climatic shifts which in turn is reducing the breeding productivity of many of these bird species, both migratory and non-migratory. A study published in Proceedings of the National Academy of Sciences has found that rising global temperatures are affecting the timing of bird migration and breeding, resulting in a mismatch between the start of spring and birds’ readiness to reproduce.
Conducted by scientists at UCLA and Michigan State University, the research shows that birds are breeding only about 6.75 days earlier despite spring arriving 25 days earlier due to climate warming. This timing mismatch is leading to a decrease in breeding productivity of around 12% for the average songbird species.
The study analyzed bird population data between 2001 and 2018 from 179 forested sites in North America. This data was correlated with remotely sensed data about vegetation timing from satellite imagery that overlapped the years studied. The researchers found that the majority of bird species were affected by the variations in the start of spring. This resulted in the birds breeding too early or too late in the season which in turn led to fewer young produced.
The researchers reported that there were some non-migratory bird species that are exceptions to this trend. For example, the northern cardinal, Bewick’s wren, and wrentit all increased brood size and frequency in response to earlier spring weather.
With climate mismatch expected to further worsen the timing mismatch — predictions are that while spring is predicted to arrive 25 days earlier by the end of this century, bird breeding will only start on average 6.75 days earlier.
One of the co-authors of the study, UCLA ecology assistant professor Morgan Tingley noted, “North America has lost nearly a third of its bird populations since the 1970s. While our study demonstrates that the worst impacts of timing mismatch likely won’t occur for several decades yet, we need to focus now on concrete strategies to boost bird populations before climate change takes its toll.”
Youngflesh, C., Montgomery, G. A., Saracco, J. F., Miller, D. A., Guralnick, R. P., Hurlbert, A. H., … & Tingley, M. W. (2023). Demographic consequences of phenological asynchrony for North American songbirds. Proceedings of the National Academy of Sciences, 120(28), e2221961120. https://doi.org/10.1073/pnas.2221961120
The Github repository contains code to assess the demographic consequences of phenological dynamics in North American birds.
Uber, H. (2023, July 3). Birds raise fewer young when spring arrives earlier in a warming world. UCLA. https://newsroom.ucla.edu/releases/birds-raise-fewer-young-when-spring-arrives-earlier