Songbirds’ Brains Hold Clues to Lingering Effects of Competition

The study by Indiana University researchers outlined how competition in the wild is encoded in songbirds’ brains and why it leaves such a long-lasting impact on animals.

An aggressive social interaction between two tree swallows. (Credit: Elizabeth George, Indiana University)

(CN) — While fighting for resources is nothing new in the wild, a team of researchers found that songbirds’ genes had been altered by competitive experiences and that aggression from fighting reverberated for days after it ended, according to a study released Monday.

Prior research has established that competition among humans for food, territory and other resources can leave a mark on long term gene activity in our brains.

Competitive experiences can carve out a map in humans’ brains that guides our bodies’ responses to future scenarios that might require us to fight.

But no prior studies have examined how the brains of wild animals are affected by scraps in nature.

Researchers from Indiana University wanted to overturn that by focusing on how competition affects wild animals’ brains and how female birds in particular demonstrate lingering effects of aggression.

As part of the study, a group of wild tree swallows were brought in to breed inside of artificial nest boxes set up by researchers.

The tree swallows are a type of songbird that cannot create its own nest but still requires one to reproduce.

Once the birds settled in their nests in early spring, researchers waited for the birds to flock to trees to roost overnight and then cut the number of available boxes.

When the female birds returned in the morning, a predictable scene followed: birds had to aggressively compete for the available nest boxes. 

Lead author of the study Alexandra Bentz of Indiana University said in a statement released with the findings that the artificial scarcity of nests was an intentional catalyst for competition among the songbirds.

“This puts incredible pressure on these female birds to compete for a cavity,” Bentz said. “We wanted to know how that competition affects the brain and what, if any, lasting effects we might see.”

A day later, the boxes were returned and the air of competitiveness was wafted away.

Researchers collected a number of songbirds during the heat of competition and again two days later and compared them to control groups captured at other sites.

Study author Kimberly Rosvall of Indiana University said that researchers wanted to understand how competitive experiences were recorded in birds’ brains.

“The project was born out of wanting to extend earlier, mostly laboratory work, from bees and mice and fish, but apply it to dynamic and interactive competition in the wild — genuine competition that occurs as animals fight for the resources they need as they struggle to reproduce,” Rosvall said.

The analysis showed songbirds who engaged in competitive events experienced altered activity in genes that were tied to energy and aggression, according to the study published Monday in the Proceedings of the National Academy of Sciences.

Genes related to energy were expressed more intensely by females at the height of competition while self-maintenance declined in the birds days after competition, the study found.

“I’ll never forget the moment when we realized the experiment had worked,” Rosvall said. “The team was spread over multiple field sites and our cell coverage was shoddy, but suddenly all of our group texts went through and we realized that each team member had accomplished their goals. After years of planning, that joy was incredible. Seeing the results only added to the feeling.”

The findings were based on measurements of gene expression and epigenetic marks, which modify DNA to link past experiences with future behavior. 

Researchers wrote that the changes in birds’ genes and hormonal signaling mechanisms showed they were prepared to react in future competitive scenarios.

“It’s exciting to think about how a totally normal competitive event for these birds — fighting for a territory — can have these lasting and potentially beneficial effects on their brain, ‘socially priming’ them to better handle competition in the future,” Bentz added. “To see competition leave a mark on the genome of the brain that outlasts the event itself is pretty amazing.”

Researchers did not immediately respond to a request for comment by press time.

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