As a teenage birder, a memorable thrill was my first visit to a bird-banding station. Researchers were capturing woodland birds in fine “mist nets” strung across a forest opening. The highlight: Helping carefully untangle a molting Scarlet Tanager from the trembling net. Like many others, however, I wondered: Wasn’t this pretty dangerous for the birds? Now, a massive new study has analyzed the risks posed by mist nets.

Mist netting has become central to studying bird behavior, movement and demographics, a team led by Erica Spotswood from the University of California at Berkeley write in Methods in Ecology and Evolution. But Spotswood discovered that there was little information on mist netting’s safety after she applied for a permit to net Gray-green Fruit Doves in French Polynesia. Concerned officials denied her permit and questioned the safety of capturing birds with nets And Spotswood found that there were no comprehensive studies that would back or refute that concern.

“I was very surprised to find that no study of this kind existed, because mist netting has been around since the 1950s and is an extremely widely used and common technique for monitoring bird populations,” said Spotswood. “In the United States at least one million new birds are banded each year at several hundred bird observatories around the country.”

To come up with some useful numbers, the researchers compiled records of documented bird injuries and mortalities from 22 bird banding organizations across the United States and Canada. The result was a dataset of over 345,000 records of capture, spanning more than 20 years of research and featuring 188 species of birds. They then looked for patterns by comparing things like bird size, age, and the frequency of capture.

The analysis revealed that birds are rarely injured or killed by mist nets. Just 0.59% of 620,997 bird captures resulted in injury, for instance, and 0.23% of captures resulted in mortality. The team also found that birds captured more frequently were less at risk than birds which were captured once. The team suggests this is because frequently captured birds are often established adults with territories; these birds tend to be in better condition than birds that don’t have territories. Finally, the researchers found that birds which were released with an injury were just as likely to be recaptured as birds without an injury; this suggests that injured birds tend to survive in similar numbers to uninjured birds, meaning the long term impact of mist netting is minimal.

“We have shown that when banders follow good practices, incidents are rare,” the authors conclude. “We hope that the results of this paper will be widely read by the banding community and that it will help researchers minimize any risk of incident.” And Spotswood notes that “what began as an inquiry for a permit application ended up evolving into something we feel will be of value to the scientific community.” David Malakoff | June 30, 2011

Source: Erica N. Spotswood, Kari Roesch Goodman, Jay Carlisle, Renée L. Cormier, Diana L. Humple, Josée Rousseau, Susan L. Guers and Gina G. Barton. How safe is mist netting? evaluating the risk of injury and mortality to birds. Methods in Ecology and Evolution (2011). DOI: 10.1111/j.2041-210X.2011.00123.x

Image © Melinda Fawver | Dreamstime.com