Birds breathalysed to check diet

A clever system allows scientists to find out what migrating birds eat, without hurting them

Migrating songbirds stop periodically to eat and store energy for the next leg of their journeys. Now, thanks to a tiny, three-valve bird breathalyser, scientists can figure out what they’re eating, and it’s not always what seems obvious.

Working on Block Island off the Rhode Island coast, Brigham Young University ecologist Kent A. Hatch led a team that sampled the breath of migrating white-throated sparrows and yellow-rumped warblers that stopped, ostensibly to feed on bayberries, before continuing south to the Caribbean.

The research was reported in the current issue of the journal Oecologia.

One breathalyser valve stem had an oxygen-filled party balloon on it, the second had a tiny mask made from a party balloon, and the third was attached to a syringe, “It all fits in the palm of your hand,” Hatch said in a telephone interview.

The team caught the birds with fine-mesh nets, put the mask on and let them breathe and re-breathe the oxygen before releasing them. They drew off the breath sample with the syringe and analysed it for isotope content in a mass spectrometer.

Hatch said the warblers ate bayberries exclusively for the previous 12 hours, the period covered by the breathalyser.

But the sparrows’ diet also included corn, millet or sorghum - probably from bird feeders, he said, because Block lsland is not known for agriculture.
“Birds can burn fat, protein or carbohydrate, and it shows up in your breath,” Hatch said.

“The advantage of the breathalyser is you don’t hurt the bird, and you can take multiple samples without any harm at all.”