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Birds are laying eggs earlier, and it’s because of climate change – Are you excited about that?

news7g03/26/2022

8 5 minutes read

Birds are laying eggs earlier, and it's because of climate change - Are you excited about that?

Hundreds of years old museum collection helps to show that birds are nesting earlier in spring

Peer-reviewed publications

FIELDS MUSEUM

Spring is in the air. Birds are singing and starting to build nests. It happens every year, like the hands of a clock. But a new study in the Journal of Animal Ecology shows that many species of birds nest and lay eggs almost a month earlier than they did a hundred years ago. By comparing recent observations with centuries-old eggs preserved in museum collections, scientists were able to determine that about one-third of Chicago nesting birds lay average eggs in 25 days. And as far as researchers can tell, the culprit for this change is climate change.

“The egg collection is a fascinating tool for us to learn about bird ecology over time,” said John Bates, curator of ornithology at the Field Museum and lead author of the study. “I love the fact that this paper combines these older and modern datasets to look at these trends over 120 years and help answer the really important questions about how climate change is happening. how it affects birds.”

Bates became interested in researching the museum’s egg collections after editing a book on eggs. “When I learned about our egg collection, I had to think about how valuable that collection’s data is and how that data is not reproduced in modern collections. ,” I said.

The egg collection itself is housed in a small room filled with floor-to-ceiling cabinets, each containing hundreds of eggs, most of which were collected a century ago. The eggs themselves (or rather, their clean, dry shell, with the inside blown out hundreds of years ago) are contained in small boxes and accompanied by labels, often handwritten, Tell me what kind of bird they are, where they are. there are words, and exactly when they are collected, to date.

“These early egg people were amazing natural historians, to do what they did. You really have to know the birds to go out to find nests and collect,” says Bates. “They pay a lot of attention to when the birds start laying, and that leads to, in my opinion, very precise dates of the eggs being laid.”

Field’s egg collection, like most, declined after the 1920s when egg collecting fell out of fashion, for both amateur hobbyists and scientists. But Bates’ colleague Bill Strausberger, a research associate at the Field, has worked for years on crowbird parasitism at the Morton Arboretum in suburban Chicago, climbing the ladder and inspecting nests to see where the crows are. The brown head lays eggs for other birds to raise. . “He had to go out there every spring and find as many nests as he could and see if they were parasitic, and it occurred to me that he had 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 nest data collected in Chicagoland starting in 1989 when he began working on it. work at the Morton Incubator. Whelan and Strausberger’s contribution to the study, Bates said, is important, because “nest finding is a lot harder than most people realize.”

“Finding nests and following their fate to success or failure is extremely time consuming and challenging,” says Whelan. “We have learned to recognize what I call ‘nested’ behaviour. This includes gathering nesting material, such as twigs, grass, roots or bark, depending on the bird, or catching food such as caterpillars but not consuming food – this may indicate the bird Parents are foraging to collect food for the chicks. Whelan and his team used mirrors mounted on long poles to peer into tall nests and keep a close eye on the date the eggs were laid and hatched.

The researchers then had two large nested datasets: one from circa 1880-1920 and another from circa 1990 to 2015. “There was a gap in between, and that’s where Mason Fidino stepped in,” said Bates. speak. Fidino, a quantitative ecologist at the Lincoln Park Zoo in Chicago and a co-author of the study, built data analysis models that allowed them to address the mid-20th century gap, as well as the mid-20th century. differences in sampling between early eggs. collectors and researchers of Whelan and Strausberger.

“Because of this unequal sampling, we have to share a bit of information between species in our statistical model, which can help slightly improve the estimate for rare species,” says Fidino. . “We all quickly realized that there could be some outliers in the data that, if not accounted for, could have a sizable effect on the results. Therefore, we have to build our model to reduce the overall effect of any outliers, if they are present in the data. “

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

In addition to illustrating that the birds are laying eggs earlier, the researchers investigated why. Given that the climate crisis has significantly affected so many aspects of biology, the researchers looked at rising temperatures as a potential explanation for earlier nesting. But the scientists ran into another difficulty: there was no consistent temperature data for the region so far. So they turned to a quantity for temperature: 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, which are very well documented,” said Bates. full. 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 neatly maps larger temperature trends, and the researchers found that it also correlates with changes in spawning days. “Global climate change is not linear over this nearly 150-year period, and therefore species may not evolve their birthdates in a non-linear manner. Therefore, we have included both linear and non-linear trends in our model,” said Fidino. “We found that the simulated data were very similar to the observed data, which shows that our model worked well.”

Changes in temperature appear to be very small, just a few degrees, but these small changes lead to different plant species blooming and the emergence of insects that can affect food availability. for birds.

“Most of the birds we looked at are insectivorous, and the seasonal behavior of insects is also influenced by climate. Bates said the birds had to move their egg laying dates to adapt.

And while birds laying eggs a few weeks early may seem like a small deal in the grand scheme of things, Bates notes that it’s part of a larger story. “The birds in our study area, up to 150 species, all have different evolutionary histories and different breed biology, so it’s all detailed. These changes in nesting dates can lead to them competing with each other for food and resources in ways they never did,” he said. “There are all sorts of really important nuances that we need to know about how animals respond to climate change.”

In addition to providing a warning about climate change, Bates said the study highlights the importance of museum collections, particularly egg collections, which are often underutilized. “There are 5 million eggs in collections worldwide, however, they have very few publications using museum egg collections,” says Bates. “They are a treasure trove of data about the past, and they can help us answer important questions about our world today.”

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