They blow on the bird to see if new pin feathers are coming in on brooding birds. Also, there is a fat reserve that can be seen. The way it was explained is that the birds come into the area exhausted. The researchers are looking to see if the local terrain is giving the birds what they need to replace their fat reserves. The fat reserves are used during the migration at an alarmingly fast rate. If they were a 150 pound person they would have to increase their weight by 50# and then they would use the entire reserve overnight. Dave Mills [email protected]