A blackbird feeds its chicks in a nest built over a rusty bonfire.  A red wooden wall is in the background, and a white downspout helps support the nest.

The timing mismatch leads to fewer birds

One of the changes with climate change is the shift in seasonality. Many regions of the world are experiencing an early arrival of spring, early flowering of plants and the emergence of insects.

The first appearance of leaves on trees, flowering plants, and greens is an important indicator that birds have started breeding. Especially for migratory birds, environmental cues such as the length of days are important triggers for birds to prepare to nest.

With the shift toward early spring, the scientists found that birds lag behind in responding to climate changes, which in turn reduce the reproductive productivity of many bird species, both migratory and non-migratory. A study published in the Proceedings of the National Academy of Sciences found that rising global temperatures are affecting the timing of bird migration and breeding, leading to a mismatch between the onset of spring and birds’ readiness to breed.

Changes in the beginning of spring due to climate change affect the breeding productivity of many North American songbirds. Photo: Caitlin Dempsey.

The research, conducted by scientists at the University of California and Michigan State University, shows that birds breed only about 6.75 days early despite spring arriving 25 days earlier due to a warming climate. This timing mismatch reduces reproductive productivity by about 12% for the average songbird species.

The study analyzed bird population data between 2001 and 2018 from 179 forest sites in North America. These data were correlated with remote sensing data on the timing of vegetation from satellite images overlapping the years studied. The researchers found that the majority of bird species were affected by changes in early spring. This has resulted in birds breeding too early or too late in the season which in turn results in fewer young being produced.

A small brown bird with a light brown breast and white lines above the eyebrow is standing on a white platform.
One species of bird that the researchers found was not adversely affected by the change of spring season was the beewick wren. Photo: Caitlin Dempsey.

The researchers reported that there are some non-migratory bird species that are exceptions to this trend. For example, the northern cardinal, beewick wren, and laurentette increased brood size and frequency in response to early spring weather.

And with the climate mismatch expected to exacerbate the timing mismatch – projections indicate that while spring is expected to arrive 25 days earlier by the end of this century, bird breeding will not begin until 6.75 days earlier, on average.

One of the study’s co-authors, UCLA Assistant Professor of Ecology, Morgan Tingley, noted: North America has lost nearly a third of its bird populations since the 1970s. While our study shows that the worst impacts of the timing mismatch are likely not to occur for several decades, we need to focus now on concrete strategies to increase bird populations before climate change affects them.

An adult swallow sits on the outside of the nest with three chicks inside.  The nest is made of mud and straw and is against a white wooden wall.
Migratory birds, such as swallows that migrate from Central America to Northern California, are affected by changes caused by climate change until the beginning of spring. Photo: Caitlin Dempsey.


Youngflesh, C., Montgomery, GA, Saracco, JF, Miller, DA, Guralnick, RP, Hurlbert, AH, … & Tingley, MW (2023). The demographic consequences of phenological desynchronization for North American songbirds. Proceedings of the National Academy of Sciences, 120(28), H 2221961120. https://doi.org/10.1073/pnas.2221961120

Github repository contains Code for assessing the demographic consequences of phenological dynamics in North American birds.

Ober, h. (2023, July 3). The birds raise fewer young when spring arrives early in a warm world. University of California. https://newsroom.ucla.edu/releases/birds-raise-fewer-young-when-spring-arrives-earlier



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