Getting Up Close with Cranes
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Central Nebraska may look like nothing but flat cornfields from a car speeding down Interstate 80, but it’s an incredibly important stopover point for millions of migrating birds, whose wings and cries fill the skies each spring. One of the most studied and iconic of these species is the sandhill crane, which has been making this annual migration for centuries. Roughly 500,000 cranes travel through Nebraska in the spring, where they descend upon the shallow Platte River, its sandbars, and nearby wetlands to rest and feed before continuing north to breed.
Much of the ground was still frozen on a March afternoon on Mormon Island in central Nebraska. This “island” runs for several miles between two channels of the Platte River. Mary Harner, director of science at the Crane Trust, led the way to a wet meadow: low-lying, undulating grasslands near the Platte, carved by older flows of the river.
Standing on an ice-covered portion of the slough roughly 20 feet across, Harner explained that once the ice melts, this area will have flowing water. These aptly named wet meadows are closely connected to the groundwater just below the surface, and they're usually marsh-like in spring and summer. Their moist soil makes it easier for birds to find bugs and plants to eat.
Scientists have studied crane migration for decades, but they're now using cameras to get an up-close view of how the birds use this critical habitat. Last spring, Harner and other researchers set up 10 game cameras over multiple sites in the meadow. The small, camouflaged cameras were programmed to take pictures every half hour or when they detected motion.
“We had cameras paired between the low wet areas and the nearby drier areas going from south to north across this island,” Harner said.
Though this habitat is critical for cranes and other migratory birds, during the last century much of it disappeared as the land was developed for agriculture or towns and cities. The Crane Trust is one of several organizations working on conserving what remains along the central Platte, using methods that mimic historic forces on this river habitat, like prescribed fire and grazing with cattle and bison.
“These wet meadow habitats are very rare. They’re one of the first habitats to be lost when river flows are diminished and floodplains are converted from their natural state. So we’re here to first and foremost protect the remaining grasslands and meadows like this,” Harner said.
Harner and her colleagues think these cameras might help them learn more about how and why the birds use these areas, which will help their conservation work.
Paul Johnsgard, a renowned ornithologist and retired biology professor at the University of Nebraska-Lincoln, has spent his career studying cranes and other birds.
“Spring biology of cranes is really important because these six weeks or so that the birds spend in the Platte Valley are critically important for them to acquire the amount of fat — energy — that they need for the rest of their spring and summer activities. So it really is important to get this kind of data,” Johnsgard said.
Crane video cameras have been around for a while, but most of the data on cranes has come from aerial surveys, thermal imaging, and people watching from wildlife blinds. Using the cameras to get thousands of up-close images offers a different way to study sandhill crane biology.
“You get an enormous sample of thousands of data points and from that you can look at them statistically and figure out exactly what percentage of time birds are doing different things. It gives a set of real data instead of general perceptions,” Johnsgard said.
That data would be almost impossible to get without human presence affecting crane behavior, according to Greg Wright, wildlife biologist at the Crane Trust. He noted that part of the initial study involved figuring out where to put the cameras. “We didn’t know exactly how they would respond to these cameras being out there. The camera is small and fairly discreet, and it’s camouflaged, but still, in a grassland anything sticks out.”
Wright said their time-lapse photography approach builds on previous wildlife studies, and cranes make ideal subjects for this kind of technology because of their “fidelity” to the Platte River, where they’ve returned year after year for centuries.
“The nature of cameras, when you can’t move them, you need a bird that has some sort of fidelity to a site. Other than nests, there’s not too many places that birds return to again and again in a way that you’d have enough images to be able to discover a pattern. Cranes fit that bill,” Wright said.
The idea for the study came from existing collaboration with the Platte Basin Timelapse project, a public/private partnership of the University of Nebraska, NET Television, and Michael Forsberg Photography, which has been collecting time-lapse images across the river system for the past three years.
Harner said changing technology has recently made these kinds of studies much cheaper and easier for researchers. Photos and videos are also more accessible for the general public than papers or graphs, Harner said, “being able show how the groundwater is pulsing and how these grasslands are essentially breathing … it just brings it to life in ways that are nearly impossible to visualize otherwise.”
Student interns helped classify more than 67,000 unique behaviors from tens of thousands of images collected last March and April. Wright said their initial findings show cranes tend to congregate in the wetter parts of the meadows, where they did more bathing and resting, compared to drier upland areas, where they mostly ate and moved around.
“I think we were surprised that there were these strong differences between the uplands and the sloughs — the water areas,” Wright said.
Camera data also offered rare glimpses of birds spending the night in the meadows rather than returning to the river as they normally do. Wright said that this spring the Crane Trust will use the cameras to study nighttime behavior of cranes on the river.
“We don’t know what the birds are necessarily doing. We know they stay on the river. But to be able to have a camera right there on the roost and see those birds throughout the night… We’ll be able to see their activity pattern through the night,” Wright said.
The project should help researchers and the public alike learn more about Nebraska’s annual winged travelers and their spring visits along the central Platte.