Cannon Netting

Subject: Cannon Netting
From: Frank O'Connor <>
Date: Tue, 21 Oct 2014 20:42:53 +0800

It still annoys me when I read criticisms of cannon netting.

I have been a member of 15 or more AWSG North West Wader Expeditions over the past 20 years as a (paying) volunteer, and I certainly plan to join future expeditions when I am available. I am not a bander. I am not the one who summarises the data and publishes papers. But every expedition I see the dedication of the people who are involved full time on the study and conservation of shorebirds. I join each expedition as an assistant, often making the leg flags, as a spotter in the hide and often the leader of a process team. I learn more about shorebirds on every expedition that I join. The shorebird families are always high on my want to see list when I travel overseas.

I have seen many important and useful outcomes from the expeditions. A few are :

1. Satellite Tracking of Bar-tailed Godwits. I admit that I was shocked when I understood how this was done. The waders are caught in cannon nets (this was not a significant threat and I was part of the team that made the catch), but then the birds were taken back to the Broome Bird Observatory where they were surgically implanted with the transmitters, with the aerial protruding from the tail. Surely this can't be good? Well all Bar-tailed Godwits survived and were released, transmitted their data for a year or more (until the battery gave up) giving important insights into the behaviour and movement of these birds (local movements, movements within WA, stopovers for some, feeding stopovers, breeding areas, post breeding areas), and they were all back in Broome the next year. This was after this was first done in Alaska, and then in New Zealand so the people involved had experience with how to look after the birds. This amount of new information learnt could not have been achieved in any other way.

2. Satellite Tracking of Little Curlews. Similar to the above, but the satellite transmitters were attached by harness. Very little information was previously learnt about this species by band and flag sightings (mainly local movements) because they are not monitored on the rest of their migration cycle. So it was not well known where they stopped over, where they bred, etc. This information was disseminated very soon after the satellite data was processed every few days, and it was a major part of BirdLife Australia's event on increasing the awareness of shorebirds in April this year.

3. Geolocators. This is fascinating. A small one gram device is attached to a large leg flag. It records the location of the bird at defined periods for as long as the battery lasts. The difference from the transmitters is that you must recatch the bird to retrieve the geolocator to analyse the data. So this has been used on birds that have a high site fidelity such as Ruddy Turnstone, Greater Sand Plover and to a lesser extent Red Knot and Great Knot. The results are amazing and show the migration paths and breeding areas. Some birds have had a second geolocator attached after the first has been retrieved, and this allows two years of data to be compared for the same individual. Do they use the same migration path? Do they use the same stopover site to refuel? etc, etc.

4. Colour Bands. I admit that I had doubts about the usefulness of this technique. As part of the Global Flyway Network project, Bar-tailed Godwits, Great Knots and Red Knots were banded with four colour bands (two each leg), one yellow leg flag (YLF) and the metal band. We had been using plain YLFs, and then yellow engraved leg flags (ELFs) and I thought that this was enough to read the flags to get the information they wanted. Then as part of the expedition we spent a day searching for and recording the ELFs and colour bands in Roebuck Bay. The colour bands are much much easier to read. You can see them from any angle. You can see then through the legs of other birds. You can see them from further away. ELFs must be birds in the open and the flag needs to be side on and you need to be relatively close to the bird. Three or more people through the GFN then spend six to eight weeks each year on the feeding sites at the Yellow Sea monitoring the birds passing through. This gives enormous information about how and where these birds feed. It shows that you can't just protect one important area. Birds move between them, and so you need to protect them all. It gives information on mortality. It gives information on population sizes. It shows local movement within Australia, giving information about how some sites interconnect.

This combination of six items on a bird is the most that I am aware of. As far as I am aware the most that are used on the smaller waders (including Curlew Sandpipers) are two legs flags and a metal band. So when I hear hearsay reports of them having seven items, I want to see the evidence. Date, place, colours and preferably a photo. But each time this claim is made, no evidence is produced. So sorry. I don't believe it.

Without this specific data on the movement of individual birds, governments won't listen. This data from leg flags and colour bands puts more pressure on the governments in the flyway to uphold their obligations under the various migratory bird agreements.

5. Cannon Netting. The teams and the procedures are very experienced and detailed now. Yes, unfortunately there are still a few birds injured at the time of firing. And this hurts the members of the team. These casualties are reported on the catch summary sheets. The birds are frozen, and sent to the WA Museum. They can't hide the casualties. There are too many volunteers. I understand that the 'acceptable' casualty rate is 1%. Maybe early on this happened. But casualties are uncommon and we usually achieve 0.2 to 0.3% over the course of a three week expedition (about 4,000 birds). With the new small mesh nets, the birds are very quickly removed from the nets and put in keeping cages covered by shade cloth. Under the hot conditions at Broome, we need to process and release the birds within about three hours of the catch. This is always achieved. Why are the birds caught? Our first goal each year is to catch enough of 10 key species to be able to estimate the breeding success (by determining the percentage of juveniles in the population). This data is important in monitoring rises and especially falls in the populations. There is a fairly high recapture rate. These birds give information about the age distribution of the population and allow better estimations of the total population. They give information about the movement of the birds. For some species, it shows that they are quite highly site specific.

6. Blood Samples. I still have some reservations about this. Some birds do struggle when they are released, and do need to be kept longer to recover. The blood samples are taken by AQIS for monitoring avian diseases in Australia. Yes, cloacal swipes are also taken. During the hysteria of the period when bird flu was an issue, these samples showed that this was not an issue for Australia. There are a few casualties of birds that have been bled. Even though this is not directly due to the normal cannon netting process, they are included as casualties in the catch report. The government would want some sort of a measure anyway on avian diseases, so it is better that the testing is done this way, than through other more drastic methods one could think of. Only a small percentage of the catch is sampled, and samples are taken on only a few of the catches in Broome. Blood sampling in the past has also been used for DNA analysis, sex determination and other purposes.

7. Isotopic analysis of Feathers. This is fascinating. If you know when during the migration cycle that a bird grows a particular feather (say a secondary covert), then by sampling that feather you can determine to a large extent where the bird was at that time. This adds to the information from other sources of how birds move and where they stopover.

8. Declines in Populations. It is claimed that the declines are due to cannon netting. But this is demonstrably untrue. The age analysis of the birds caught show this. The Shorebirds 2020 surveys at sites where there is no cannon netting show this, and the number of flagged birds in these areas are very low. The birds caught show a high site fidelity. But the people making the claims do not read the papers, or the survey analysis. I guess the less you know, then the more things that you can imagine might happen, even if they have already been proven to be untrue.

9. Raptors. It is true that some birds in the past have been caught by raptors as they are released. But the procedures have been changed and there were none on last year's expedition. There are lookouts posted for raptors. Birds are released in groups rather than individually if there is any risk of raptors being around. It is everyone's responsibility to lookout for raptors. I don't believe that this is an issue any more.

Where do I learn about these things? By being a participant in the expeditions. By being a member of the AWSG. It is sent by email. It is published in Stilt and Tattler (published by the AWSG). It is published in international journals. It is on the AWSG web site. It is disseminated at shorebird conferences. Some of it is communicated on the GFN web site. This information and much more is available through cannon netting, and it does further the conservation of these species.

There are vacancies for next year's expedition. You do not need to be a member of the AWSG. It is not a holiday! There are early starts, heat, humidity, lots of other tasks. But there is some time for general birding. We look for a team of 23 to 25 people so we can safely catch 250 to 300 birds in a catch. If we catch less then we fully process each bird (band, flag, age, moult, weight, wing length, etc). If we catch more then we reduce the amount of processing so that the birds are released well before the three hour limit (at least band, flag, age). There are tasks for people of all levels of experience and fitness.

The people involved in cannon netting care more about these birds than anyone, and do everything they can to promote the conservation of these species. They put their time into it. It is grossly unfair for them to be criticised.

Frank O'Connor Birding WA Phone : (08) 9386 5694 Email :

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