Birds nest earlier and climate change is to blame

Marrakesh, March 28 (Morocco-Actu) –

Many birds are nesting and laying eggs nearly a month earlier than they did a hundred years ago due to climate change, a new study published in the journal Nature. Journal of Animal Ecology.

By comparing recent sightings with centuries-old eggs kept in museum collections.Scientists were able to determine that about a third of the birds that breed in Chicago lay eggs after an average of 25 days. And from what researchers can tell, The culprit of this change is climate change.

“Egg collection is a fascinating tool that allows us to learn more about the ecology of birds over time,” said Dr. in a statement John Bates, curator of ornithology at the Field Museum and lead author of the study. “I love this paper that combines these ancient and modern datasets to look at these trends over about 120 years and help answer some really important questions about how climate change is affecting us. How about birds.

Bates became interested in researching museum egg collections after editing a book on eggs. “When I learned about our egg collection, I started thinking about the value of the data in this collection. and how these data are not reproduced in modern collections”, he say.

The egg collection itself is housed in a small room with floor-to-ceiling cabinets, each containing hundreds of eggs, most of which were collected a century ago. The eggs themselves (or rather, just their clean, dry shell, the contents of which were banished hundreds of years ago). They come in small boxes and come with a label, usually handwritten, indicating what type of bird they are and where they are.

“Those early egg-beaters were great natural historians, for doing what they did. You really have to know the birds to go find the nests and collect them,” Mr. Bates said. “They are very attentive when the birds start to lay and in my opinion, resulting in very precise spawning dates. »

Field’s egg collection, like most collections, failed after the 1920s, when egg collecting fell out of fashion with hobbyists as well as scientists. But Bates’ colleague Bill Strausberger, a field research associate, has worked for many years on oral thrush at the Morton Arboretum in suburban Chicago, Climb ladders and inspect nests to see where the brown-headed cuckoo has laid eggs for other birds to raise.

“I have to go out there every spring and find as many nests as possible to see if they are parasitic, so I know I have data on modern nests,” says Bates. Chris Whelan, an evolutionary ecologist at the University of Illinois at Chicago, also contributed to the modern dataset with songbird nesting data collected in the Chicago area since 1989, when he started work at the Morton Incubator. Whelan and Strausberger’s contributions to the research are important, says Bates, because ” Finding nests is a lot harder than you think. »

“Finding nests and following their fate to success or failure is time-consuming and challenging,” says Whelan. “We have learned to recognize what I call ‘nesting’ behaviour. This includes collecting nesting materials, such as twigs, grass, roots or bark, depending on the bird species, or capturing food, such as caterpillars, but not consuming the food; this may indicate that the parent is foraging for the chicks”. Whelan and his team used mirrors mounted on long poles to peer inside high-altitude nests and closely monitor egg laying and hatching dates.

The researchers then had two large nested datasets: one from circa 1880-1920 and the other from circa 1990-2015. Mason Fidino was involved,” said Mr. Bates. Fidino, a quantitative ecologist at the Lincoln Park Zoo in Chicago and a co-author of the study, built models for data analysis that allowed them to fill in the gap in the mid-20th century, as well as in the mid-20th century. sampled differences between eggs from the original collectors and Whelan and Strausberger’s study.

“Because of this unequal sampling, we had to share some information between species in our statistical model, this may help slightly improve the estimate for rare species.“, said Fidino. “We all quickly realized that there could be outliers in the data and, if not accounted for, they could greatly affect the results. For this reason, we have to build our model in a way to reduce the overall effect of any outliers, if they are in the data.

The analyzes revealed a striking trend: of the 72 species for which historical and modern data are available in the Chicagoland area, about one-third are breeding earlier and earlier. About birds whose nesting habits have changed, laid the first eggs 25.1 days earlier than 100 years ago.

In addition to illustrating the fact that birds lay eggs earlier, the researchers looked for a reason. With the climate crisis already having an enormous impact on many aspects of biology, researchers have considered rising temperatures as a possible explanation for early nesting. But the scientists discovered another downside: there’s been no consistent temperature data for the region since that time. So they turned to one temperature indicator: the amount of carbon dioxide in the atmosphere.

“We couldn’t find a single source of long-term temperature data for the Midwest, which is surprising, but you can estimate temperatures with carbon dioxide levels, Very well documented“ said Bates. Data on carbon dioxide comes from a variety of sources, including the chemical composition of ice cores from glaciers.

The amount of carbon dioxide in the atmosphere over time is clearly linked to broader temperature trends, and the researchers found it also correlates with changes in spawning dates. “Global climate change is not linear over this nearly 150-year period and it is therefore possible that species have raised their spawning dates non-linearly. That’s why we include both linear and non-linear trends in our model,” he explains. Fido. ” We found that the simulated data was very similar to the observed data, indicating that our model performed well. »

The temperature change is obviously small, only a few degrees, but these small changes lead to the flowering of different plants and the appearance of insects, things that can affect the food available to the bird.

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