Wednesday, July 21, 2010

Cannon Netting*

One of the only ways to catch large numbers of shorebirds away from the breeding grounds is to use cannon nets. Cannon nets are exactly what they sound like. They are nets that are propelled by small cannons. While I was in Chile, I learned the basics of cannon netting, and in the process, realized that it is difficult, and whether or not a firing is successful depends a lot on luck. Cannon netting requires a bit of reconnaissance work, namely to figure out where the high tide roost sites for the target birds are. Once that key piece of information is acquired, the team can then proceed to set the net up the next day. Now, because birds are caught on their roost site, it is necessary to set the net up well before high tide, which often means setting it up at low tide, when the birds are dispersed, so that we have enough time to hide before birds are considering roosting.

Step 1: So, the first step of cannon netting is to set the net and the cannons up. This step is fairly straight forward, although the exact placement of the cannons does certainly require an experienced eye. The placement of the net is also important, because if the net isn’t in the right place, then it may turn out that no birds end up in the catch area. Now, the catch area is an area that is about 30 ft. by 30 ft., so the margin of error is quite small. Anyway, to set the net up, first, we need to dig a shallow trench to place the net in. It was important to make sure the leading edge of the net was on top, otherwise it wouldn’t fire properly. Next, we needed to dig the holes for the cannons, and attach the ropes of the nets to the projectiles of the cannons. Okay, now the net and the cannons are set up.

The net trench is dug, and now the net can be laid out in the shallow trench.

One of the two cannons that are placed at either end of the net. Here, the bottom is wrapped in several plastic bags to prevent them from getting wet

Step 2: The next important step of cannon netting is to disguise the net. I enjoyed this part, because, if done right, the net and cannons should be almost invisible. Some sites were far easier to camouflage than others, and for some sites, we got quite creative. Now, this wasn’t as easy as just piling seaweed and algae on top of the net… the layer of cover had to be thin and light, so as to not weigh the net down and hinder firing (we actually made this mistake once). If all goes well, there should be very little evidence of the net area.

Adding sedge clumps to further hide the net.

Step 3: The next step is to wait. And wait some more. Usual wait times ranged from 3-6 hours… it all depended on how fast the birds began piling into the roost area. This part was both boring, fun, depressing, and stressful.

Step 4: The second to last step of cannon netting is probably one of the most important. It involves twinkling and jiggling. Now I don’t know where these names came from, but they are fun to say. Twinkling is to gently push birds toward the catch area. Sometimes this involved flushing birds from an alternate roost site farther down the beach in hopes that they would move to the roost site where the net was set. Other times, it would involve trying to gently push birds a few meters to try and position them better in the net area. Regardless, twinkling was important, as its success often dictated how many birds ended up in the catch area. When twinkling failed, it usually means birds flushed and flew away and didn’t come back. Jiggling is usually the last step before actually firing. Jiggling is done by jiggling the jiggler. The jiggler is a small rope about 2 meters in front of where the net is set up. The point of jiggling the jiggler is to get birds out of the zone 2 meters in front of the net. Those two meters are called the “danger zone.” The “danger zone” is the area in front of the net where birds could be injured by the net. So, by jiggling the jiggler, one was able to safely and effectively move birds out of the “danger zone” without making all the birds in the capture zone fly.

The flock is in place...

Step 5: 3….2…1… FIRE!

Step 6: Run like hell to the net to get birds out (if it is a “wet catch,” where birds are caught in the net in the water, you run like hell faster). After removing birds from under the net, they are placed in keeping cages, which are simple cages that are set up to keep birds in and keep them calm.

While removing birds from under the net, we would cover the net with a dark tarp to keep them calm. Birds would then be placed in the keeping cages, where they would wait to be banded.

Step 7: Process birds as fast as possible. Now, when there is the potential of catching up to 200 birds in a catch, this sounds easier than it actually is. Birds that we caught would get a metal band, a color band (indicating the year it was caught), and a unique color flag with a code on it (the color of the flag indicates the location it was banded: red is for Chile, orange for Argentina, green for Alaska, and white for Churchill). Birds would be checked for their molt condition, have their bills, head length, and tarsus length measured, and some would have blood taken for later genetic work.

The assembly line of godwit banding. This would ensure that we could process at peak efficiency.

Step 8: Release birds!

*No birds were harmed during our stay in Chile while cannon netting

1 comment:

  1. I'm really glad to have come across this post. I'm hoping to do some netting for catching seabirds and waterfowl for my project and I'm glad you've laid cannon netting out here so nicely for us. I did not realise the cannon apparatus is so large. A great deal is required for this procedure.