Australia, Bird Study, Expeditions and Travels, Science, Uncategorized

Australia Road Trip – Cannon Netting Shorebirds

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Ghost Crab holes, and the sandy remains of excavation, on 80 Mile Beach


Our first catch with cannon nets at 80 Mile Beach, in the late afternoon, gave all of us a real sense of accomplishment.
After two days of experimenting with small-mesh nets (setting one high and one low), the team leaders, Clive, Roz and Chris decided to go back to the same method that has proved successful in the past — two large-mesh nets set at the same level of the tide. It was a tough call for several reasons . . . . .

The small-mesh net, the standard on the Delaware Bay, is made of small mesh that prevents birds from getting entangled so extraction is relatively simple. On direction, the team first secures the sides of the net with sand or rocks so birds cannot escape, then at the water’s edge they lift the net so birds can walk up-beach to the back of the net. Afterward they are covered with shade cloth.

 

At water’s edge, the team begins to lift a small-mesh net to allow birds to walk up-beach to the back of the net after a capture on Roebuck Bay

Although small-mesh nets have always been around, lighter materials have allowed them to grow in size, now about 22 meters by 10 meters, without growing in weight. Weight has two impacts. First, it causes the net to deploy poorly especially in an opposing wind. Second, if the birds are caught near the water line, the weight of the net could cause birds to drown, especially small birds. The small mesh exacerbates the problem because the birds can’t pop their heads through the mesh. Overall, however, lighter material has made small-mesh nets more versatile and the ease of extraction greatly reduces risk to the birds.

A small-mesh net caught by an opposing wind in Chiloe Island, Chile. The net ballooned and all birds escaped

The large-mesh net has two advantages: it is relatively light-weight and has less wind resistance. This has several effects. First, the net can deploy more efficiently and can be fired in most wind conditions. Second, the larger mesh and relative low weight allows the net to be much bigger and have a much larger catch area. Third, the birds have an easier time in water because the net is lighter and they can easily pop their heads up through the mesh.

Birds caught in a large-mesh net on 80 Mile Beach

As in all things, the problems with large-mesh nets is the consequence of its merits. The birds get tangled in the large mesh, just as they might in a mist net, and so extraction requires the deft hand of experienced extractors. Many of the people from the Broome Banding Team, South Australia Wader Group and the Victoria Wader Study Group are experienced so we had plenty of good extractors when we made our first catch of 345 birds with the large-mesh net. The catch included good samples of Great Knot, Curlew Sandpiper, Grey-tailed Tattler and seven other species including Red Knot, Bar-tailed Godwit, Common Greenshank, Sharp-tailed Sandpiper, Greater Sand Plover and Marsh Sandpiper.

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The following three photographs, taken by Hugh Hanmer of the UK, are of two large-mesh nets being firing simultaneously on 80 Mile Beach

(Above) the “cloud” behind the nets is comprised of sand used to camouflage the net and some smoke from the black powder used to power the projectiles

The net is deployed quickly, before birds can lift from the ground . . . .

. . . . . and settles down over the birds like a blanket

 

The next day we made a another catch, smaller, 76 birds. It was “high in quality” as Clive says because it included an adequate sample of Red Knot and Common Greenshank — species that are harder to catch. The second net caught White-winged Black Terns and Common Terns. After just two catches, the team performed with great coordination and skill, even with a much more complicated net.

Chris Hassell holding a White-winged Black Tern with Frank O’Connor looking on.

One of the main skills of securing a catch made with large-mesh is the preparation that takes place after the net fires over the birds and before extraction. This is most important if the tide is still rising and the net, with birds entangled, must be moved up the beach out of range of rising water. If the team lifts the net onto their forearms and pushes it up the beach (as is the procedure with small-mesh), folds will develop and the birds will become entangled in multiple layers of net. Extraction would be more complicated. A better way is to lift and push the net up away from the waterline while a second group pulls the back side of the net up-beach at the same time. This requires great presence of mind because the birds are still caught in the net by wings, feet and head. The process is not for the reluctant. The leaders must act quickly and decisively and the team must act with great coordination. Done well, as it is by Clive, Chris and Roz, the birds come out in excellent condition and ready to be processed.

Roz Jessop, Clive Minton and Maureen Christie direct the team to lift the net while they pull up the back end

After this procedure is complete, the birds are covered with shade cloth to calm them and keep them cool. Meanwhile, the teams work on setting up keeping cages. When cages are ready for birds, experienced extractors free the birds from the net and the rest of the team takes them to the keeping cages. After all birds are in the cages, shade cloth covers them to keep the birds calm and cool. On 80 Mile Beach, a 20-knot sea breeze is enough to keep the mesh-like cages well aerated and the birds cool. If there is no sea breeze, Chris directs the team to erect a shade tent built from poles and shade cloth. Then the scientific work begins.

The team covers birds in a large-mesh net with shade cloth

Keeping cages being erected after the birds are covered

After the keeping cages are erected, birds are extracted by experienced banders and taken to the cages in holding boxes or by hand

Finally, the keeping cages with birds are covered with shade clothe

Nick Ward holding a Marsh Sandpiper