National Wildlife Refuge System

Landmark Success for Whoopers

This year's nesting season for whooping cranes at Necedah Refuge, WI, has been the most successful since the refuge began working to establish a self-sustaining population in 2001.
Credit: USFWS

June 23, 2015 - This year’s nesting season for the federally-endangered whooping crane on Necedah National Wildlife Refuge, WI, has been the most successful since the refuge began working to establish a self-sustaining population in 2001.

But while a new method of increasing whooping chick survival rates has shown success, Necedah Refuge staff still faces challenges even as they are increasingly optimistic about the whooping crane population.

The cranes were introduced to Necedah Refuge in 2001 from chicks hatched at Patuxent Research Refuge, MD. Since then, adult survival rate, migratory success and egg production rates have steadily improved in the flock known as the Eastern Migratory Population (EMP). The most recent success has been due to a refuge/university partnership that is solving the black fly problem that has caused major nesting failure.

Black flies, which swarm adult cranes and their nests, emerge on the refuge each year around late May. The flies feed from the birds and their eggs, forcing mature cranes from their nesting grounds. Since 2011, refuge staff has focused in part on limiting the impact of black flies.

Necedah Refuge staff is increasingly optimistic about a new method of increasing chick survival rates called "forced re-nesting."
Credit: USFWS

 In 2011 and 2012, the Whooping Crane Eastern Partnership (WCEP), of which Necedah is a founding member, attempted to reduce black flies by introducing a natural pesticide into two rivers on the refuge. While black fly numbers dropped, only two chicks survived the 2012 season -- and the problem of chick mortality remained.

Last season, Necedah Refuge partnered with the University of Wisconsin at Stevens Point to try a new method of increasing chick survival rates, called “forced re-nesting.” Researchers take eggs from whooping crane nests that are unlikely to be successful before the annual emergence of black flies. The chicks are then transferred to captive rearing facilities. The refuge expects affected adult cranes to make new nests, increasing the overall number of healthy chicks in the long-term.

Before last season, the technique was never attempted with whooping cranes, but enjoyed success in sandhill crane populations in earlier tests.

When Necedah Refuge continued forced re-nesting this year, more nests succeeded in producing healthy chicks than any time in the refuge’s 76-year history. While 27 pairs of cranes nested this season, producing more than 20 chicks, 16 nests successfully hatched at least one egg; 11 chicks are still alive.

“We’ve gotten further than any other whooping crane repopulation effort in 15 years,” said Brad Strobel, wildlife biologist at Necedah Refuge.

 The forced re-nesting experiment is still in its infancy, with only half the resident cranes undergoing the process. The other half is serving as a control group. Coupled with a season that saw significantly less black flies on the refuge than in recent years, WCEP researchers are cautiously optimistic.

However, black flies are not the only hazards to young cranes at Necedah. The refuge is also home to other predators, as well as wide expanses of wetland that may not provide the birds with enough food to raise offspring. Refuge staff is in the process of identifying and assessing these other threats to determine the next steps towards the cranes’ long-term survival.

Despite challenges with the cranes' reproduction, the WCEP has seen definitive results in other aspects of re-establishment. From 2001 to 2011, researchers taught the EMP to migrate in the fall by using ultralight aircraft to lead the birds from Necedah Refuge to Florida refuges. These flights, organized by Operation Migration, Inc., continue each year, though in recent years they have been launched from White River Marsh Wildlife Area, also in Wisconsin, rather than Necedah Refuge.

“Hatching chicks is one part of the solution,” said Strobel. “Seeing those chicks fledge and later return as mature adults to raise their own offspring will complete the picture.”




Last updated: June 23, 2015