Sunday 25 February 2024

Shelduck Migration Project

At the cannon netting session on 19th February the group took part in a shelduck research project which aims to identify the risks to migrating individuals from collisions with offshore wind farms.  The research is being carried out by Ross Green from the BTO.

Shelduck don't perform the classical spring and autumn migrations between breeding and non-breeding sites like most migrant birds. Instead they migrate in summer – from mid-June to early August – to large estuaries to moult before moving on to wintering sites, which may or may not be near their breeding areas. All the known offshore migration routes pass through areas  that may have offshore wind farms in future. The likelihood of interaction is therefore high, but it is unclear if the interactions will have any effect at the population scale, or an impact on migratory routes in the long term.

GPS data shows that these ducks mostly fly at night, and at heights above sea level that put them at risk of collision with turbine blades. 

Isotopes in the feathers of shelduck may be site specific and so it is hoped that each moult site will have a unique chemical signature. Analysis of feather samples could help to identify the movements of shelduck. 

Our group collected small fragments of secondary feathers at our cannon session and these will help the project by showing where our birds go.

Snipping a section of feather for analysis. 

GPS data has been unable to establish where birds go after they've moulted, so this feather analysis will help to fill that knowledge gap. This method is also considerably cheaper than GPS tracking. 

Robin Pearson

Saturday 10 February 2024

Cannon netting 11/2/24 ....or not!

The catch area at Seaton Marshes had been baited with grain since the last cannon netting session, and decent numbers of ducks and waders, including Shelduck & Black-tailed Godwit, had been seen feeding in the area. The cannon net was set up yesterday, and a team of 12 keen ringers attended for the catch this morning. At one stage there were about 30 Shelduck on the scrape, but they refused to feed on the grain and then flew off. At about 945am the decision was made to give up & disassemble the net. 

The catch area during the week (photo: Adrian Bayley)

The net set & ready (photo: Adrian Bayley)

The disappointed Team 

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