14 DAY TRIAL // Researchers have recently published the results of a new study, which shows that songbird populations in the United States could be getting smaller. After controlling for other factors that may be contributing to this phenomenon, the team could only conclude that global warming and climate change are the most likely culprits. The investigation analyzed well over 500,000 individual birds, belonging to more than 100 species. The results held throughout the study, which means that a correlation must exist, the BBC News reports. Details of the research appear in the latest issue of the respected scientific journal Oikos.
The group learned that, throughout these species, wing spans tended to get smaller. The overall weight of the animals is also apparently decreasing, the experts mention, adding that these changes were produced within the last 50 years. This means that the trend is very recent, and that external influences, such as global warming, are to blame. As any biologist would tell you, the Bergman Rule is very simple – in warmer climates, all animals tend to become smaller. The group, however, highlights that it found direct proof that warming is harming the birds directly. They are simply shrinking in response to the changes in their environment.
The birds that were investigated in this research were all analyzed at the Pennsylvania-based Powdermill ringing station, which is owned by the Carnegie Museum of Natural History, in Rector, Pennsylvania. Expert Robert Mulvihill and Robert Leberman, both at the museum, collaborated closely with colleague Swiss colleague Dr Josh Van Buskirk, who is based at the University of Zurich, for the research. More than 486,000 birds were caught and analyzed at the station between 1961 and 2007, and each of them was also measured. In their experiments, the scientists looked for possible trends in these measurements. The birds also included species that flew around the year, not just seasonal ones.
The group looked at 83 species of birds that were caught while they were migrating in the spring. Over the 46-year study period, 60 of them had become smaller, with shorter wings, and a lower average body weight. Out of the 75 species that were caught while performing their autumn migration, 66 were smaller at the end of the study than when the investigation began. “So many of these species are apparently doing just fine, but the individual birds are becoming gradually smaller nonetheless. […] as temperatures become warmer, the optimal body size is becoming smaller,” Dr Buskirk reveals.