By Chris Skeldon 
Scientists have long assumed that birds migrate during the winter to save energy. The logic was quite clear: apart from extreme cold, birds would need to expend less energy to stay warm.
According to Mongabayone New research changes this assumption. study published In the magazine Nature ecology and evolution It was concluded that a group of Eurasian blackbird (Tordus Merula), a partially migratory species, spending time in warmer regions, did not conserve energy when compared to populations of the same species that remained in a cold environment.
“We suspected an energy deficiency in resident birds, but there was no significant difference between their net energy expenditure compared to migratory birds,” he said. Niels Linklead author and researcher at the Max Planck Institute for Animal Behavior. “If there is no overall energy benefit, there must be other evidence or reasons for migration.”
As part of the study, researchers developed Biologists Which have been surgically implanted in birds. Sensors in recorders Measure heart rate and body temperature every 30 minutes.
Heart rate is an indicator of energy expenditure, the more energy you use, the higher your heart rate. “It was like looking through a keyhole into their internal systems, as if they were using a device Smart watch“Linick said.
Over the course of three years, starting in 2016, the team managed Sensors installed in 118 birds In southern Germany. Externally linked radio transmitters allowed scientists to monitor whether birds were alive or dead, as well as follow their movements. In the end, the team got more than… 890000 measurementsfrom the recorders he took from 83 birds.
“We ended up with an innovative picture of what these birds do to support their migration,” he said. Scott Yankoco-author and researcher at the University of Michigan School of Environment and Sustainability. “They modulate their heartbeat and their entire metabolic regulation in really complex ways.
Analysis of data on heart rate and body temperature helped scientists calculate the birds' daily energy intake. They found that migrating birds began to lower their heart rates and body temperature by nearly a degree Celsius A month before departure to save energy for the trip. In theory, their energy expenditure should decrease when they reach their destination. But this was not found to happen.
“It doesn't show up in the heart rate data,” Yanko said. “There is energy going through their system that is not being accounted for.”
The discoveries left the team together Interesting questionsThat is: where did that energy go? If there is no biological benefit to migration, why do so many birds do it?
Linek and Yanco raise the hypothesis that Migration must have hidden costs Which may include immune function, the energy needed to stay alert in a new environment, or competition from other birds in the area to which they have migrated. “Clearly the benefit of thermoregulation is offset by something else that is more difficult there.”
While searching for answers to these questions, Linick said he wanted to take advantage of “revolution Biologists“ To collect more data and better understand how “environment is transmitted through bird physiology and its energetic regulation.”
Understanding physiological responses to migration will also help scientists predict how this occurs Climate change and deterioration Home It may affect future migration patterns.
“Predicting where and when the animals will be, what is causing their numbers to increase or decrease, and how we can intervene to change those things,” Yanko said. “These are the questions we have to answer.”
