Wednesday 7 February 2024

Cannon netting 13/01/2024

The group undertook its first cannon netting session of the year at Seaton Marshes. The catch area had been baited for several days. The net was set on the afternoon before the catch day by a few members of the group

Setting the net and the cannon

Weather conditions on catch day were ideal - cold with light winds – as about 15 members of the group waited for the bang of the cannon to send them scurrying down to the net. 27 birds were caught, which was about 2/3 of the birds in the target area. The catch comprised 22 shelduck, 3 teal, one wigeon and one moorhen. 16 of the shelduck were re-traps.

The catch safely bagged and ready for processing

All new shelduck were fitted with a metal BTO ring together with a yellow colour ring with large black lettering which can be read in the field using binoculars or a telescope. 

Fitting a plastic colour ring

Next we determine the sex of the bird and its age. The most obvious difference in the sexes is that males (usually) have a noticeable knob on the bright red bill. The female’s bill is duller.

Female (1st bird shown) and male shelduck for comparison

The principle ageing character is the obvious white tips to the secondaries in immature birds, which give the wing a distinctive white trailing edge in flight. In adults the secondaries are either all black or have only narrow white tips.

Adult birds. Although the 1st bird shown has narrow white tips to the secondaries they are not the broad white tips that would be seen in a 1st winter/spring bird.

Then it’s time to get some biometric measurements: the length of the wing chord (from the bend in the wing to the tip of the longest primary feather); head + bill length; tarsus length (from the notch in the ‘elbow’ to the bend of the foot) and the bird’s weight.

Tarsus measurement is taken from the notch behind the elbow to the bend of the middle toe

Taking measurements and giving them to one of the most important members of the team – the scribe

The team busily at work. 

And away! Birds are released at the water’s edge where they can choose to fly or swim away

Gathering in the net at the end of the session

The three oldest re-trap shelduck were all at least 10 years old and had been re-caught or re-sighted at Seaton Marshes on multiple occasions as detailed in the table below. They were each given the age code 6 at ringing and because age code 6 means ‘hatched before previous calendar year’ they were at least 2 calendar years old when ringed.  

The typical life span of a shelduck is 10 years and the oldest shelduck recorded (maximum age from ringing) was 19 years 7 months (BTO data) so our old birds have not done too badly!

Robin Pearson