Southern Colour Ringing Group

10 October 2019

Southern Colour Ringing Group Brent Goose study update

Introduction

Of the five trackers fitted two failed after a short period, one failed in mid-April and one on the 1st May. The final tracker stopped sending data back on 6th June. Work has been undertaken with the suppliers and, as all these trackers are under warranty, all will be replaced at no cost. The supplier has also identified the possible reasons for failure and this can be rectified along with a re-design of the collar, which we hope will help with some issues of feather loss around the base of the neck.

Tracking Results

BRAN01 (Green CD) Adult Female (paired with Green CF)

Figure 1 - BRAN01 one of the Brent Geese ringed and satellite tracked on 7th January at Blue House Farm

This transmitter gave data from 7th January to 22nd February when it stopped transmitting and gave 243 location fixes. The bird stayed in the Crouch Estuary for the whole period, apart from one trip to the coast on 5th February see Figure 2. We do, however, know this bird was still alive as of 5th May. BRAN01 was observed on Hallig Hooge (an island in Germany) with an un-ringed bird and what was thought to be its mate CF. Clearly this bird made the migration, although unfortunately due to tracker failure, we were unable to track the route and timing to Germany. However, the three birds we did track all took a virtually identical route so we are assuming this bird took a very similar route.

Figure 2 - Map for BRAN01 showing four data points each day from 7th January 2019 to 22nd February 2019

BRAN02 (Green CA) Adult Male (apparently un-paired)

This bird stayed in the Crouch estuary until 2nd April (Figure 3) when it moved out to the coast just off Foulness and remained there from 10pm until midnight at which point it flew directly across the North Sea covering 340km in 6 hours (Figure 4).

Figure 3 - Map for BRAN02 showing four data points each day from 7th January 2019 to end of March 2019

Figure 4 - Map for BRAN02 showing the route over the North Sea on night of 2nd and 3rd April then the remainder of April 2019

After a short stop on Richel in Netherlands, this bird then moved to Terschelling where it remained until 11th April.

On 11th April, it moved onto the Dutch mainland and remained there until late May. At the end of May, the bird moved very quickly to Germany and then across northern Germany/southern Denmark and on 6th June stopped transmitting whilst staging in Denmark (Figure 5).

Figure 5 - Map for BRAN02 showing the second movement to Denmark at the end of May up to 6th June.

BRAN03 (Green CC) Adult Female (Paired with Green DL – also a transmitter bird)

This bird’s transmitter operated from 7th January to 29th January giving 91 location fixes whilst it worked, all in the Crouch Estuary. We know this bird was still alive some weeks after the tracker stopped working as it was observed by David Low at Blue House Farm. It remained in the Crouch Estuary for the whole period. This bird was very faithful to roosting on Bridgemarsh Island and feeding on the grazing fields at Blue House Farm and along the Crouch (Figure 6).

Figure 6 - Map for BRAN03 showing the faithfulness to the Crouch up to 29th January 2019.

BRAN04 (Green DL) Adult Male (Paired with Green CC – also a transmitter bird)

This bird remained in the Crouch Estuary until 9th March (Figure 7) when it moved overnight to the Dutch Wadden Sea (Figure 8). It remained here for one day and then on 10th March it took a further flight to Simonsberg in Germany where it remained until 1st May. Unfortunately, on 1st May, the signal appears to have gone down on this tracker and there is no evidence that this bird died so we are unfortunately in a position where it looks like this tracker has now also failed. This tracker gave 732 location fixes whilst it worked.

Figure 7 - Map for BRAN04 showing the faithfulness to the Crouch up to 9th March 2019.

Figure 8 - Map for BRAN04 showing the movement on 10th March and staging up to 1st May 2019.

The staging in the German estuary, as in the Crouch, showed a very limited area used and Figure 9 shows the area the bird was faithful to through the whole of April 2019.

Figure 9 - Map for BRAN04 showing the faithfulness to the German Estuary up to 1st May 2019.

BRAN05 (Green CM) Adult Female (Paired with Green DD)

This bird remained in the Crouch Estuary from 7th January until 13th March (Figure 10).

Figure 10 - Map for BRAN05 showing the faithfulness to the Crouch up to 13th March 2019.

On 13th March it under took an overnight flight direct to the German Wadden Sea with an apparent short stop on the sea off the coast of The Netherlands. On arrival, it remained for a very short time on Juist before moving to Nordeney where it remained until 20th April (Figure 11).

Figure 11 - Map for BRAN05 showing the route taken on 13th March 2019 to the first staging point in Germany.

This bird then moved on 20th April some 60km further east and gave data for a couple more days before stopping transmitting (Figure 12).

Figure 12 - Map for BRAN05 showing the final jump east from the staging area in Germany up to 23rd April when data stopped transmitting.

Summary

The data supplied by the five transmitting birds has yielded some interesting facts. The maps shown above are taken from tracking of four data points a day. However, we are able to interrogate further the system and settings and were also monitored with half hourly data-points downloaded via SMS. This has allowed us to be a little more confident in our analysis and suggestions regarding bird movements and site fidelity.  

Firstly, within the Crouch Estuary in Essex we discovered that all the birds were incredibly faithful to the grazing fields at Blue House Farm and local area within a 7km range either side of the river. It also appeared that the north side of the river was favoured and birds used grazing fields rather than crops, which are predominantly on the south of the Crouch. The birds also seemed to favour roosting on one of three saltmarsh areas with the favoured and most used being Bridgemarsh Island. However, other areas of salt marsh were used for roosting at various times, for reasons unknown.

The three birds that were tracked migrating from the UK to their staging areas all made the move at night. Most of them took around six hours to do the 300+ km journey to reach the Dutch coast. All three left around midnight and made landfall at dawn. Analysis shows that the first thing they seem to try to do is find fresh water, probably for a drink and a bath. All three left the Crouch Estuary around 10pm and spent up to three hours just off the coast of Foulness Island before leaving around midnight and flying direct across the North Sea in a shallow curved line towards the north-west coast of The Netherlands. All three seemed to take an almost identical route.

One bird staged in The Netherlands and two in Germany. What has also become clear is that on each staging ground the home range is also quite small and birds are faithful to very tight and small areas. The following is a rough calculation of each home range on each staging area:

BRAN02 – 12km of the Terschelling coast and 4km of the Dutch mainland and no more than 1km from the coast.

BRAN04 – 7km of the German coast where it staged with a couple of apparent trips up to 5km.

BRAN05 – 2.3km of the coast of Nordeney and no more than 1 km off the coast.

It is somewhat disappointing that all of the trackers failed so quickly. Work with the Company has established that there were likely design faults with the neck collars. At least two will be replaced with a modified design and our proposition is to trial these two replacements next winter to see if this improves the return rate of data. We hope to take a further catch this coming winter and fit the replacement satellite trackers to continue the study of Brent Geese in the Crouch Estuary.

Paul Roper for the Southern Colour-ringing Group

11 August 2019

We have had our first Common Tern sighted at Dungeness by Martin Cassmore. Clearly on the way south let's hope it gets seen a few more times.

11 August 2019

Thanks to the wind and the cancellation of the Walthamstow Wetlands Wildlife Fair I decided to put a couple of spring traps out in the field this morning. The reward was three Red Kites by 9am. All juvenile birds all three were wing tagged before wing measurements and weights were taken then released.