We usually use rocket nets to capture them in Pennsylvania. The capture site is baited with corn and is re-baited daily to keep the swans interested in feeding. The net is placed in a line six to eight feet in front of the bait. The net and rockets are camouflaged into the surrounding soil or field stubble so not to alert the wary swans. Each rocket contains an explosive charge that when ignited propels the rocket and attached net upward and over the unsuspecting swans.
Researchers detonate the charge from a remote blind when the birds are actively feeding on the bait.
Usually, it takes several days for the swans to get comfortable with coming into and feeding at the bait site. In the winter and early spring, swans feed primarily on waste grain or on winter wheat in the large agricultural fields of Lancaster and Lebanon counties. When swans are captured, they are carefully removed from the net and placed in a temporary holding pen separating juveniles from adults. While the age of swans can be determined easily by plumage coloration, determining the sex is more difficult. It requires a cloaca examination.