Spring is here and starts a whole new natural cycle, in which animals and plants seem to reactivate after winter lethargy. However, global warming is changing patterns established for tens of thousands of years. Birds, for example, are laying their eggs earlier each time, due to the advancement of the warm season due to climate change.
A study that has just been published in Journal of Animal Ecology shows that many species of birds are nesting and laying eggs nearly a month earlier than they were a hundred years ago. By comparing recent observations with centuries-old eggs preserved in museum collections, scientists have been able to determine that about a third of the bird species that nest in the Chicago (USA), study area, have advanced the laying of eggs in an average of 25 days. And as far as researchers have been able to verify, the culprit for this is climate change.
“Egg collections are a fascinating tool for us to learn about bird ecology over time,” says John Bates, a bird keeper at the Field Museum and lead author of the study. “I love the fact that this paper combines ancient and modern data sets to look at these trends over roughly 120 years and help answer really critical questions about how climate change is affecting birds,” he added.
“Finding nests and following their evolution to success or failure is time-consuming and challenging,” says Chris Whelan, an evolutionary ecologist at the University of Illinois at Chicago. That’s why Whelan and his team They used mirrors mounted on tall poles to see what was going on inside the nests so they could check the dates the eggs were laid and hatched.
Thus, the researchers had two large nesting data sets: one from roughly 1880-1920 and one from 1990 to 2015. “There’s a gap in the middle, and that’s where Mason Fidino came in,” says Bates. Fidino, a quantitative ecologist at Chicago’s Lincoln Park Zoo and a co-author of the study, built models to analyze the data that allowed them to bridge the mid-20th-century gap.
The analyzes showed a surprising trend: of the 72 species for which historical and modern data were available in the Chicago region, about a third were nesting earlier and earlier. Those birds whose nesting habits had changed were laying their first eggs 25.1 days earlier than a hundred years ago.
In addition to illustrating that birds are laying eggs earlier, the researchers looked for an explanation for this phenomenon. Since the climate crisis has dramatically affected so many aspects of biology, the researchers looked to rising temperatures as a possible explanation. But they found another snag: There is no consistent temperature data for the region going back that far. So they turned to an indicator of temperature: the amount of carbon dioxide in the atmosphere.
The researchers found that this indicator was also related to changes in egg-laying dates. “Global climate change has not been linear over this nearly 150-year period, and therefore species may not have advanced their laying date uniformly,” Fidino noted.
Changes in flowering and insects
The temperature changes are apparently small, only a few degrees, but These small changes translate into the flowering of different plants and the appearance of insects, things that could affect the food available to the birds.
“Most of the birds we see eat insects, and the seasonal behavior of insects is also affected by climate. Birds have to change their egg-laying dates to adapt,” says Bates.
And while the fact that birds lay their eggs earlier than normal may seem like an inconsequential event, Bates points out that it’s part of a larger story. “The birds in our study area, more than 150 species, have different evolutionary histories and different breeding biology. These changes in nesting dates could cause them to compete for food and resources, which was not the case before.& rdquor ;, he explains.
As well as serving as a warning about climate change, Bates says the study highlights the importance of museum collections, particularly egg collections, which are often underutilized.
“There are five million eggs in collections around the world, and yet very few publications use them,” says Bates. “They are a treasure trove of data about the past and can help us answer important questions about our world today,” she says.
Reference study: https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.13683