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SAN JOAQUIN RIVER NWR: Nets Aren’t Just for Catching Fish – Rocket Nets Used to Capture Aleutian Cackling Geese During the Annual Banding Event
California-Nevada Offices , December 20, 2014
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An Aleutian cackling goose captured at the San Joaquin River NWR.
An Aleutian cackling goose captured at the San Joaquin River NWR. - Photo Credit: USFWS
Once captured by the rocket net, geese are processed and banded by federal and state personnel, as well as volunteers.
Once captured by the rocket net, geese are processed and banded by federal and state personnel, as well as volunteers. - Photo Credit: Rick Kimble
USFWS Fire Captain Keith Mayer and CDFW Biologist Melanie Weaver process a captured goose at the San Joaquin River NWR.
USFWS Fire Captain Keith Mayer and CDFW Biologist Melanie Weaver process a captured goose at the San Joaquin River NWR. - Photo Credit: USFWS
A rocket net is launched over a flock of Aleutain cackling geese during the banding operation at the San Joaquin River NWR in California.
A rocket net is launched over a flock of Aleutain cackling geese during the banding operation at the San Joaquin River NWR in California. - Photo Credit: Rick Kimble

By Madeline Yancey

It is a cool fall morning in the San Joaquin Valley and visitors have come to the San Joaquin River National Wildlife Refuge (NWR) in Stanislaus County near Modesto, Calif., to experience the spectacular concentrations of migrating waterfowl and other waterbirds that make their home in the Valley during the winter.

Tens of thousands of Ross’, snow, and greater white fronted geese, as well as hundreds of lesser sandhill cranes, draw visitors to the refuge, but perhaps the stars of the show are the more than 50,000 Aleutian cackling geese.  These small geese, the size of an extra-large duck, were listed as endangered in 1967, and later removed from protection under the Endangered Species Act in 2001. The delisting of the Aleutian goose was possible, in part, because of the protection of the species’ major winter grounds – land that is now part of the San Joaquin River NWR.

The observation deck provides a perfect place for observing the Aleutian goose and others from about mid-October to mid-March each year. Distant wetlands provide roosting habitat for the geese, but better than that, the deck is surrounded by refuge “farm fields,” fields that are planted with crops like winter wheat and corn. At various times throughout the fall, winter, and early spring, the crops are mown to make them accessible to the foraging geese. Wheat and corn provide critical high-carbohydrate foods for geese that have just flown 1,500 to 2,000 miles from their nesting grounds in the Aleutian island chain of Alaska. The forage crops also help the geese fatten up, gaining body mass prior to their return trip in the spring. The giant flocks of geese swirl in and land in one field then advance like battalions of ground troops to the other, driven by their ravenous appetites. Meanwhile, observers are treated to the awe-inspiring sights and sounds of the foraging flocks.

Others are drawn to this spectacle, as well. Teams of wildlife management personnel from the U.S. Fish and Wildlife Service and the California Department of Fish and Wildlife are there to take advantage of the impressive concentrations of Aleutian Cackling geese for another reason. In the fall of each year, Refuge and State staff members strive to capture and band at least 400 Aleutian Cacklers. The geese are banded to monitor the size of the species’ population, important because the species was once listed as endangered; it is a hunted game species and population data allows state game officials to set season dates and bag limits; and the goose’s population has now grown to the point that it could cause problems on agricultural lands in some areas.

Goose species are often captured for banding during the summer while on their nesting grounds. Breeding season captures are relatively easier. Geese are flightless during their breeding season because they are molting at that time. Many species also concentrate into huge nesting colonies of thousands to millions of individual birds. Under those conditions, biologists can literally herd the birds into pens and capture them by hand. However, that tactic is not effective with the Aleutian cackling goose. During its breeding season, the Aleutian goose population is spread across more than 150 islands and the 1,200-mile length of the Aleutian Island chain. The time to find this species in large concentrations is while on its wintering grounds.

The technique used to capture geese that can fly is “rocket netting.” Rocket netting is more technically challenging than herding geese into big “corrals.” Goose nets must be of a mesh size small enough to prevent escape while the banders rush to gather the captured birds. The gauge of the netting must be strong enough to hold a hundred frantic, flapping, biting birds trying to escape, yet light enough to be carried airborne by the rockets. The net must also be fired at just the correct angle from the ground, ideally about 30 to 40 degrees. The net is stretched out in a straight line in a baited area – in this case, a mown corn field. The net is folded on itself, accordion fashion, and camouflaged by covering with vegetation. One side of the net is anchored to the ground. The other side is connected, at intervals, to “rockets.” Each rocket is an iron projectile attached to the net and housed in a canister. Each canister holds a charge of gun powder that is fired by a hardwired electronic fuse. The rockets carry the net aloft, over the feeding geese, to the ground on the other side.

While the feeding geese march towards the net, oblivious to its presence, the banders wait patiently in their vehicles until the birds are close enough to fire the rockets. The birds cannot be too close to the net lying hidden on the ground because, at the least, being hit by the net would keep it from launching properly and at worst, birds struck by the net could be injured or killed. On the other hand, birds located too far out or too near the net’s edges could escape.

When enough birds are in position, a plunger is pushed, the rockets fire and the net is launched sailing over the feeding geese, then settling down on them, restraining them on the ground. When the banders arrive, time is of the essence. The birds must each be freed from the net before they injure themselves or succumb to stress. Each one is placed inside a cotton sack then set with its companions to “chill out” in the shade of the vehicles. One by one the birds are retrieved from their sacks and processed in assembly-line-fashion.

First, they are carefully examined to determine their gender and whether they are an adult or juvenile. Next, they receive a lightweight aluminum numbered band on their left leg and a large blue plastic band bearing an alphanumeric code around the neck. The data is recorded and each goose is gently released – flapping and cackling – back to their companions that usually remain feeding a short distance away. The neck band allows the birds to be identified by observers using spotting scopes to pick them out from large flocks of geese at other times and locations throughout the season. Observing the proportion of banded birds to unbanded ones in various flocks enables wildlife biologists to calculate accurate estimates of population size.

Over the course of four days, nine Fish and Wildlife Service personnel, four California Department of Fish and Wildlife staff, and more than a dozen volunteers captured and banded nearly 400 Aleutian Cackling geese at the San Joaquin River NWR. Those geese will join their kind in providing population data needed to monitor the success of a species that has recovered from a mere few hundred birds in the early 1970s to an estimate exceeding 200,000 birds today.

 

Madeline Yancey is a park ranger and visitor services specialist at San Luis National Wildlife Refuge Complex in Los Banos, California.


Contact Info: Jack Sparks, 209-826-3508, jack_sparks@fws.gov
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