Bird banding program at Delaware Nature Society monitors birds in two states as part of national program

As Ian Stewart carefully untangles a squawking mockingbird from the links of a mesh bird net, the resident ornithologist at the Delaware Nature Society frowns.

“Mockingbirds make a lot of noise, but it’s not being hurt,” he says in his Newcastle, England accent.

With the bird cradled safely in one hand, he points at a purple streak of fresh bird poop on his thigh.

“Pokeberry,” he says with a smile. “Hazards of the job.”

In the past three years, Stewart has handled thousands of birds in a similar fashion (in the first five months of the program, he captured 413 birds) as part of the DNS’s ongoing bird banding program.

From April to November, Stewart and any number of random volunteers set up broad nets at various locations to catch birds long enough to log their statistics and carefully attach a serial numbered band to one of their legs.

The birds are quickly released from their nets and spend a few minutes in a burlap bag for their safety as Stewart measures their bodies and bands their legs, reading out numbers to an assistant who logs the data in a field book, with the whole process taking between 10 and 20 minutes.

The data ultimately goes into a USGS database that will be used to track an individual bird’s migration patterns, which in turn shows what areas need to be preserved to best suit the birds as they travel long distances.

Started as a pilot program in 2015 to “track breeding and migratory bird use of different early successional habitat regimes in the Red Clay Valley,” the banding program has also evolved to show what effect certain invasive species have on the bird population.

To that end, Stewart has set up 10 plots at Bucktoe Creek Preserve in New Garden Township, Pa., where invasive plants multiflora rose and oriental bittersweet were removed and 10 where they remained in place.

Stewart watches the plots for nests and other signs of bird use, with the goal of finding out what invasive plants they’re eating – and subsequently spreading – and removing those plants from their migratory paths.

“Porcelain berry is actually very pretty, but it’s a problem because the birds eat the berries and then poop them out, and they’re spreading the plant,” he said. “The same with oriental bittersweet.”

Last August, Stewart also oversaw the installation of a new hi-tech Motus (Latin for “movement”) tower at Bucktoe.

Looking somewhat like an old-school television antenna, the tower is actually used to track birds that have been tagged with nanotags that emit a signal distinct to each device.

The solar powered tower will pick up the signal of any bird so tagged that flies within a 15km radius; that data is then saved to a memory card that Stewart retrieves every few weeks.

Stewart said the data collected will show information on the effect of weather patterns and time of year on migration. It will also help scientists and biologists to better understand the mysteries behind migration.

Stewart said most birds migrate at night, with the belief that they navigate by the stars; it’s also safer, with fewer predators like hawks abound. 

“Because it’s happening at night, we don’t know much about it,” Stewart said. “This way, you can tell who’s going in what direction, and also how long they’re staying in each area.”

Originally used to collect data on shorebirds, Stewart said the information shows what areas need to be preserved from development to help improve the birds’ living conditions.

“It’s a real conservation application,” Stewart said. “And you don’t need to actually catch the bird to know it is migrating.”

An array of Motus towers stretches diagonally across Pennsylvania to the Lake Erie region. There are also several in New Jersey and a few in Delaware, including one at the Bombay Hook National Wildlife Preserve in Smyrna.

“There’s an entire network of them across North America, and they’re hoping to spread it to South America and Europe,” Stewart said.

In the past year, the Bucktoe tower has detected over a dozen migrating birds, including thrushes that were banded further up north and flying south, and several shorebirds banded in the south that are headed north for the winter.

“I’m really excited for this fall, because the birds are just beginning to migrate south,” Stewart said. “I’m hoping we’ll collect a lot of data this year.”

Volunteers are needed each Wednesday for the bird banding program between April and November at Bucktoe on Wednesdays and the Ashland Nature Center in Yorklyn on Mondays, from 8 to 11 a.m.

For more information, visit