Studying Sandhill Cranes

Sandhill crane project to help Colorado Parks and Wildlife understand changing migration patterns of Rocky Mountain population.
Sandhill Cranes
Sandhill Cranes

It wasn’t long ago when a spotting of a greater sandhill crane in the area of Delta on Colorado’s Western Slope was an infrequent occurrence. But in the last two decades, that has changed in a big way. Colorado Parks and Wildlife researchers are on a mission to find out why.

In February, a team of Colorado Parks and Wildlife biologists, researchers, and staff teamed with the U.S. Fish and Wildlife Service and coordinated with local landowners in the Delta area to get an opportunity to net greater sandhill cranes in an effort to affix Global Positioning System (GPS) transmitters to a small population of the roughly 4,000 migratory birds that have come to call Delta a more regular home than previous generations.

Sandhill Crane is fitted with a GPS transmitter.

“There is a lot of local interest in what is going on with these cranes, how they’re doing in Colorado and looking at the much bigger picture of what is happening across their entire range,” said CPW Avian Research Chief Jim Gammonley. “With migratory birds, we manage these species that live across political boundaries with other states and the federal government, and every partner is interested in what is happening with these cranes in Colorado.”

Historically, the Rocky Mountain population of greater sandhill cranes has primarily bred in the spring and summer months in Idaho, Montana, Wyoming and Utah along with parts of northwestern Colorado.

In the fall, the entire population would funnel south through Colorado’s San Luis Valley down into wintering areas in Arizona, New Mexico and Mexico. When temperatures warmed up coming out of winter, the cranes would repeat the process and come back north through the San Luis Valley during the spring migration into traditional summer areas.

But Gammonley explained that the migratory pattern has changed for a percentage of the Rocky Mountain population. During the last 10 to 12 years, CPW has seen the area around Delta and Montrose, which had previously served only as a spring and fall stopover area for the birds during migration, become a wintering area for the cranes.

“We’re seeing this segment of the population that uses the more northern states for summering area leaving pretty late in the fall and then just moving down to the area around Escalante State Wildlife Area,” Gammonley said. “They are spending the winter there and then going north again in the spring. They never go down into the San Luis Valley and further south to normal wintering areas.

Sandhill cranes migrate through Colorado’s San Luis Valley.
Sandhill cranes migrate through Colorado’s San Luis Valley.

“We want to find out exactly which birds are doing this, why they are doing it and how it affects the long term population dynamics.”

Gammonley teamed with CPW biologist Evan Phillips out of the Montrose area office and Dan Collins, a U.S. Fish and Wildlife Service biologist, to coordinate February’s capture project. The team opted to use rocket netting, a commonly used technique used to live-capture large numbers of birds and wildlife.

The capture teams would bait a specific area of Escalante State Wildlife Area where nets had been set up and aim to lure as many cranes under the net as possible. Rocket nets use explosives to launch the netting over the animal, making timing key for a successful capture.

With only one chance per day to lure in as many cranes as possible, patience was the name of the game. After a few long days, a couple of close calls and working in adverse weather conditions, the team successfully detonated a rocket net and captured cranes underneath.

In total, 13 sandhill cranes were captured. Seven were outfitted with GPS transmitters, and six more were marked with numbered and colored leg bands that will allow researchers across the Rocky Mountain range to identify the marked birds.

A total of 13 cranes were captured using a rocket net.

“The cranes are pretty feisty and feistier when trying to get out of the net,” said Phillips. “We are very careful when we handle and process them. With the big beaks they have, we have to be very careful in how we control their heads.”

Gammonley credited inter-agency teamwork along with strong relationships created with private landowners for the success of such projects.

“Partnerships between wildlife agencies and private landowners are critical,” he said. “Sandhill cranes use public lands for part of their needs, but they are absolutely dependent on surrounding private lands for places to meet their needs. Having good communication about what is happening, what landowners are seeing, what they want to see and listening to their concerns is how we all work together to manage a healthy population of cranes.”

A sky full of Sandhill cranes.

The USFWS began marking sandhill cranes with GPS transmitters in the Rocky Mountain population in more traditional wintering areas along the middle Rio Grande River Valley in New Mexico in 2014. Since that time, more than 100 cranes have been marked with transmitters, and at least 10 of the birds with GPS trackers have started to use the Delta area as wintering ground in subsequent winters, Phillips said.

The hope is to get a couple years of data off each marked crane, and some GPS transmitters have continued to provide data for as much as four or five years, Gammonley said.

Cranes are among the oldest living species on the planet, with fossil records dating back 9 million years. The birds that migrate through Colorado are the largest of the North American sandhill crane subspecies standing 4-feet tall with a wing-span of up to 7 feet and weighing in at 11 pounds.

The Rocky Mountain population of greater sandhill cranes is estimated at roughly 20,000 birds. Gammonley said it has been stable for a long time after careful management helped steadily increase numbers since the 1940s. Like many wildlife populations, numbers had been greatly reduced prior to that time from hunting and habitat changes.

Gammonley’s hope now is that data gained from February’s project will help CPW and its partners continue to maintain a strong population in a world-changing once more.

“We have seen in these last few decades not only some population growth but also these distribution changes in their ranges,” he said. “Whether that’s from various land use changes through their range, climate issues or what have you, it is clear these birds are shifting around their annual migratory patterns.

“These are really incredible birds, and being part of a project like this is one of those ‘highlight’ type things in terms of activities you do in this business.”

capture team
The Sandhill crane capture team.

Written by John Livingston. John is the Southwest region public information officer for Colorado Parks and Wildlife.

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