Corps Partners in International Black Tern Population Study

Amy Redmond
Natural Resource Specialist, Willamette Valley Project

The U.S. Army Corps of Engineers biologists at Fern Ridge Reservoir have banded together with researchers from Eastern Connecticut State University, Loras College and Oregon State University for an international population study to better understand why an overall decline of black tern is occurring throughout their range.

An adult North American black tern sits on a tree stump at Fern Ridge Reservoir.

An adult North American black tern sits on a tree stump at Fern Ridge Reservoir.

Found across North America, black terns typically inhabit lakes and wetlands that have emergent vegetation. The declining number of terns observed during previous decades are associated with the loss of wetlands, which the birds use for nesting and foraging.

Beginning at Fern Ridge Reservoir during the 2016 breeding season, Assistant Professor Don Lyons of Oregon State University, Corps Wildlife Biologist Garrett Dorsey and Northwest Youth Corps intern Miranda Martin successfully captured 10 adult black terns. The group collected a small blood sample for genetic analysis and banded each bird with a numbered metal band, then released them back into their nests. The bands allow researchers and bird watchers to report sightings of individual black terns to a national database. This information will allow researchers to better understand the movements and range of the black tern throughout its life cycle.

The mottled eggs of a North American black tern sit in a nest of grass reeds at Fern Ridge Reservoir.

The mottled eggs of a North American black tern sit in a nest of grass reeds at Fern Ridge Reservoir.

Dorsey said capturing and collecting blood samples has to be timed perfectly to minimize disturbances to the breeding birds and to reduce the risk of unwanted chick mortality or nest abandonment by the adults.

“The trapping effort should be timed so the adults have been incubating the eggs for approximately two weeks, which tends to prevent the adults from abandoning the nest due to the disturbance. black terns typically start laying eggs at Fern Ridge Reservoir in late May and juveniles fledge in mid-July,” said Dorsey. “If the attempted capture occurs too soon in the nesting period, the adults could abandon the nest for the remainder of the season. If the attempted capture occurs too late after the eggs are hatched, the resulting disturbance could cause mortality of the newly hatched chicks.”

The black tern population research is led by Dr. Patricia Szczys, an associate professor of biology at Eastern Connecticut State University, and Dr. David Shealer, an associate professor of biology at Loras College. Their research includes sites in the Provinces of Alberta and Ontario, Canada and in Michigan, Maine, Wisconsin, Nebraska and Oregon.

Don Lyons of Oregon State University (left), and Miranda Martin of Northwest Youth Corps tag an adult North American black tern at Fern Ridge Reservoir.

Don Lyons of Oregon State University (left), and Miranda Martin of Northwest Youth Corps tag an adult North American black tern at Fern Ridge Reservoir.

Dorsey explained the one site in Oregon – at Fern Ridge Reservoir – provides a unique opportunity to study the genetic variability of a population, since it is the furthest breeding population from the center of the black tern’s range and the only location west of the Cascade Mountains where they breed.

“Thanks to this study and our partnership with these universities, we can continue to build on the knowledge we have of black terns and to use it to increase the population size here at Fern Ridge,” said Dorsey. “One future project that will start in 2017 will use artificial nesting islands to see if we can utilize more of the available habitat at the lake. This project may also provide us with answers about why this species prefers some areas more than others.”

The current genetic study at Fern Ridge Reservoir will continue through the 2017 breeding season.