Understanding the Spring Migration Ecology of Soras and Virginia Rails

By Chad Cremer, Auriel M. V. Fournier

A brown, gray, and black bird wears a tag and is held by a research. In the background is a wetland. — Virginia rail with a tag. The black line at the rear of the bird is the antennae of the tag. Photo courtesy Forbes Biological Station.

Sora (Porzana carolina) and Virginia rail (Rallus limicola) are small, secretive marsh birds from the Rallidae family, which includes rails, coots and gallinules. These rails are approximately the size of an American robin with large feet, cryptic plumage, and a short, stubby tail. More often heard than seen, these secretive birds are elusive within dense wetland vegetation.

During the breeding season, sora and Virginia rail are widely distributed across much of the lower 48 states of the U.S. and southern Canada and spend the winter months in the southern coastal states of the U.S., Mexico and Central America.

Although sora and Virginia rail are considered the most abundant rails in North America, monitoring their population status and distribution has been difficult as they are rarely seen by people. Migration is an especially important time of year to study rails since migration is a risky time of year. Adverse weather, patchy suitable habitat, and scarcity of food during migration can have a negative impact on rails survival and health. These short-term negative impacts can have what is called a ‘carry-over effect’ where negative health impacts in one season impact the next, in this case, the breeding season.

A gray, brown, and black bird with a yellow bill is held by a researcher. In the background are tan grasses. — A sora caught at The Emiquon Preserve. Photo courtesy Forbes Biological Station.

Studying Spring Migration Ecology

To sustain a healthy population of rails across North America requires them to be healthy entering the breeding season so they have the energy and resources they need to successfully reproduce. Our project focused on studying the spring migration ecology of sora and Virginia rail since we know spring migration is crucial to setting these birds up for a successful breeding season. As a result, natural resource agencies want to identify and manage migratory stopover sites to support migratory birds while they recover and refuel during migration.

Our study is the first to evaluate the timing of spring migration and stopover duration of sora and Virginia rail in Illinois. We were interested in determining when sora and Virginia rail were migrating through central Illinois during the spring, how long they stopped within the Illinois River Valley, and what factors influenced their departure decisions.

We trapped sora and Virginia rail at Emiquon Preserve and Banner Marsh State Fish and Wildlife Area in Fulton County using walk-in confusion traps outfitted with a solar-powered audio lure. From 2021-2023 we caught and banded 162 sora and 395 Virginia rail in spring. Of those banded, 68 sora and 120 Virginia rail were tagged with a pulse-coded transmitter (i.e. Motus tag).

Bird traps installed in a wetland by researchers. Two birds are caught in the traps. — A rail trap early in the season before the vegetation has sprouted. You can see two rails in the catch box on the right. Photo courtesy Forbes Biological Station.

Motus Tracking Network

The Motus Tracking Network is an automated telemetry system, such that when a bird with a tag flies by a tower, it is detected, and we are able to assess when they leave a site and also track their migration across the region. The earliest Virginia rail was captured on March 23 and the earliest sora was captured on April 8. We found peak migration was on April 23 for Virginia rail and May 1 for sora. The average stopover duration at Emiquon Preserve was 10 days for sora and 13 days for Virginia rail.

Rails tagged earlier in the season had longer stopover durations than rails tagged later in the season. We found that cloud conditions and moon score affected departure decisions and that more rails departed on clear dark nights. On average, rails depart one hour after civil twilight, which is when the brightest stars in the sky start to become visible.

Bird traps surrounded by vegetation are installed in a wetland by researchers. — A rail trap later in the season, once the vegetation has grown up more. Photo courtesy Forbes Biological Station.

The regional detections of tagged birds suggest sora and Virgina rail migrating through central Illinois primarily travel northwest from the Illinois River Valley towards the Prairie Pothole region. Rails use wetlands dominated by non-woody vegetation, often the same wetlands used by waterfowl and other wetland-dependent wildlife. This work helps inform what time of year rails need wetlands and adds to our collective understanding of what different species of wetland wildlife need from our wetlands in Illinois.

Chad Cremer finished his Masters in Natural Resources at the University of Illinois Urbana Champaign in May 2024. He has worked on a variety of avian research project, from whip-poor-wills to wood ducks.

Auriel M.V. Fournier is the Director Forbes Biological Station, Illinois Natural History Survey.

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Question: Has there been any studies done on the fall migration?