This is a phenomenon that we probably would not observe ourselves, but the watchful eye of scientists will not miss anything - it is thanks to them that we learn that the world of birds is undergoing major changes recently.

Birds are getting smaller and, like many other phenomena recently observed, this is to be the result of climate change. Researchers from the University have analyzed data collected on migrating birds - about 70,000 individuals - for the last 40 years and concluded that during this time they significantly decreased while their wings grew. Interestingly, this analysis was possible thanks to the involvement of one researcher from the Chicago Field Museum, who measured all these individuals for a long time!

That it is not a nice job, because it is about birds that fell on buildings and died, which is a very common phenomenon in some places. It is estimated that every year about a billion birds die as a result of collisions with windows and glass surfaces of buildings that they cannot see, and the Chicago Hancock Center or Sears Tower are one of the biggest "killers". Scientists have decided, however, that the suffering of birds will not be in vain and will benefit science, which is why volunteers regularly bring bird corpses to the said museum, where they are accurately measured and cataloged.

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This is very important because measuring wild bird populations is very difficult, and therefore carried out very rarely and irregularly. Thanks to the collected data, it was possible to determine that in recent years birds have lost significantly in size and at the same time their wings have grown, and scientists have no idea why this happened - they are convinced that this is about climate change, but the exact mechanisms are still remain a mystery.

Scientists have tracked 52 migratory species that are subjected to tremendous effort and stress during annual expeditions - record holders cover 44,000 miles! Just like falling asleep, they need adequate body mass to survive such an exhausting journey. Why are they getting smaller? It may be about global warming, which means that birds do not incur such high energy expenditure due to maintaining proper body temperature, but at the same time their metabolism must be at their highest speed to feed the wings longer, and longer wings are to facilitate this task.

“We believe that increasing the wing length represents a compensatory adaptation to sustain migration while reducing body weight, which results in increased metabolic cost during flight” the researchers say. In short, since flapping wings costs more, these can be just as long to achieve the most benefits at the same caloric expenditure. Researchers found that there was a significant increase in temperature in the hatching areas in summer, which coincides with the theory of weight loss due to temperature rise. Therefore, they will conduct further research to better document the phenomenon and see if these are the only adaptive changes that occurred in birds.