A study has found an increase in the size of birds captured in central California, a trend that may be caused by climate change.
Researchers from San Francisco State University analysed data that had been gathered over the past 40 years by PRBO Conservation Science and the San Francisco Bay Bird Observatory (SFBBO). The data came from monitoring programmes that looked at diverse species of songbirds and hummingbirds.
The researchers found that the length of the birds’ wings has increased over the last 27 to 40 years. They also discovered that the birds are gaining body mass, although the change in mass is not as pronounced as the change in wing length.
Considering that the result is prevalent in the majority of the birds captured in central California, researchers think that the reason for the increase is likely to be climate change. The findings of this study, which was published in the Global Change Biology journal, are inconsistent with previous studies that animal body size decreases as climate becomes warmer.
Rae Goodman, first author of the study who did the research when she was a graduate student at San Francisco State University, says the study demonstrates that the effects of climate change on animals vary according to the environment the species are in.
“In some locations, such as a cold climate, rising temperatures may be most important, which could cause birds to shrink,” said Goodman. “In other areas, such as a dry California climate, the increased weather variability may be more important.”
A rise in rainfall levels caused by climate change in California, for example, would allow plants to thrive better, leading to a rise in plant-eating insects that many of the birds feed on. With a greater food supply, birds would grow bigger.
“More storms, droughts, or cold snaps could [also] kill off smaller birds, leaving only their larger counterparts,” Goodman added.
Goodman says that the PRBO and SFBBO are currently conducting further research on the effect of climate change on birds.
Image: author’s own