Cannon Netting (Poll Results)

Subject: Cannon Netting (Poll Results)
From: Frank O'Connor <>
Date: Wed, 14 Mar 2001 00:28:54 +0800
At 12:57 13/03/2001 +0000, Night Parrot wrote:
Other frequent comments such as c-n participants
show a general lack of competence relating to
wader field identification and that many can
confirm id, only when a bird is held in the
hand needs to have further qualification

How about utter b**ls**t! Is that qualified enough or should I say "complete and utter"? I doubt that you even received one such comment since messages that I have sent with you in the address list have bounced. And I similarly doubt that there even was an "informal poll".

However you asked some questions that I have enough information as an observer and an assistant to answer.

3.  How are the cannon nets positioned to ensure that the nets when
fired do not hit birds? What are the prescribed minimum distances that are maintained between birds and the proposed arc of fire? If minimum distances vary depending on the size of the nets and the species targeted, what are the actual measurements by which a competent operation can be assessed?

The net is set based on the high tide mark and where it is estimated that it will be. The aim is for the front of the net to only just land in the water. There are markers placed where the front of the net is expected to reach. There are two metre markers placed on either side of the net. The net is not fired if any birds are between these two metre markers and the net. The firing position always has good vision of the catching area (a hide is built if necessary), and the observers have binoculars if needed. The two metres is independent of the net size. The cannons are pointed up at a slight angle (plus the beach is sloped) and will clear any birds further away than two metres. This is seldom a problem as the birds are usually lined up along the water's edge and at least two or three metres away from the danger area. The birds get slowly pushed up the beach by the tide and the net is fired when they are in the target area and before they approach the danger area. The only time there is a problem is when the target species are small plovers which walk up the sand. In this case there is usually a "jiggler rope" which helps to move the birds outside the danger area. It is not really accurate to say that there is an "arc of fire". The net goes straight out.

4.  Please show the actual formula used to
measure the maximum holding time for
captured birds, considering variable
factors such as weather, local environment
etc. as well as information regarding acceptable
trauma and stress tolerance levels for each species?

There is no "actual formula". Nor should there be or could there be. The remaining birds are monitored for heat stress as they are being banded. In hot weather the holding cages are put on the wet sand to keep the birds cooler. Shade is always erected over the holding cages so that they don't heat up. The birds are quiet in the cages. The largest birds are banded first to avoid leg cramps. Any birds sitting on the sand are banded next but this is rare. Remember that the birds are caught at high tide when they are roosting. They would be standing anyway, and they are not losing feeding time.

8.  What is the worst-case scenario for
the birds (not the nets) and what standards
can be implemented to avoid these disasters?
What happens when the projectiles misfire or
explode or when only one side fires off?
What happens when the wrong sized birds get
caught in the wrong sized mesh?  Is it common
practice to cut nets to release tangled birds
or is that only done reluctantly as a last resort.

You obviously have not been involved in cannon netting if you ask these questions. There is only one sized mesh. There is usually only one net, or sometimes two. The birds are not caught by being tangled in the net, but rather by being caught between the net and the sand. A few birds get their head or even a wing through the net before they are extracted, but they are easy to extract (far far easier than mist netting).

11.  What adequate "no trapping, wader protection
areas" are set aside for the birds to enjoy refuge
from cannon netting(not the Simpson Desert)?  Should
there be a seasonal ban put on trapping migrant
birds , at least prior to their departure? Please
define some acceptable standards to satisfy this concern.

There definitely should not be bans just prior to their migration (or just after arrival). This is the very time when the most important information is collected about moults, weights, age distributions, migration patterns, etc. For instance, one Great Knot banded in Broome was found in Hong Kong or China 7 days later, and based on the weight at banding before departure it was estimated that it did not depart for one or two days after banding. Hence it flew from Broome to Hong Kong in one non stop leg. I don't think that areas need to be set aside. For instance in Broome, the largest flocks are generally left alone, because you would either catch too many birds to process, or because the depth of the flock from the tide line is too high and the risks would be too high.

When nets are moved during trapping exercises, is
this usually done to minimise net aversion
learning by birds to increase the catch rate, or
is it done for the welfare of the birds?

Neither. Again you have clearly not participated to ask this question. Different sites are selected based on the tide height. The slope of the beach and all sorts of other factors make certain sites best at certain tide heights. As birds return to the same general area, if you did catch at the same site you would very likely be catching many of the same birds. Retraps give the most valuable information, but generally not when it is only one or two days before recapture. Even if they are not the same birds you would be getting too many of the same species and one of the aims is to get representative samples from as many species as possible so that statistically significant comparisons can be made.

I believe that there are a lot of superstitions about net aversion. The net is always lightly camouflaged in dry sand but I can't say that I have ever seen birds lined up either side of the net with none in front.

Frank O'Connor      Birding WA
8C Hardy Road                      Email : 
Nedlands  WA  6009                                ICQ : 14655047
Phone : +61 8 9386 5694

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