Med Gulls by the Arun: Update

A large number of Mediterranean Gulls were present at the gull roost on the eastern bank of the River Arun just south of Arundel for much of July 2018. More than 20 had colour rings on their legs, giving an insight into their origins and movements. This analysis was written on 16 August and updated on 19 September to reflect the receipt of additional data.

Numbers rose from between one and five birds at the start of July to 42 on 11 July, rising the next day to 97 before falling back. Numbers jumped again a week later, with at least 84 birds by the river or foraging in the adjacent water meadows on 18 July at high tide, when it appears that birds otherwise spread out along the lower reaches of the river became concentrated at the site.

Gulls at the Arun roost in July 2018

Species/Date	9	11	12	13	14	16	17	18	21	23	26	27	30	31	2/8
Med. Gull	1	42	97	42	16	4	72	84	72	132	28	10	3	2	0
Common Gull	3	9	9	20	13	1	10	10	9	3	7	6	1	1	5
L. Black-backed	4	1	1	2	1	1	0	0	0	0	1	0	1	2	0
G. Black-backed	1	2	2	2	1	1	0	1	0	0	0	2	1	0	0
Bl-headed Gull	245	255	112	170	90	41	412	268	200	110	115	73	33	59	30
Herring Gull	118	118	56	87	55	59	241	81	98	165	123	60	89	105	56

Note: Tide, weather, disturbance and time of day can lead to major differences in the number of birds present.

By high tide on 23 July there were 132 birds. Of these, 42 were in juvenile plumage, a much increased number and percentage of the total. Numbers fell to 28 on 26 July, when half the birds were in juvenile plumage and most of the rest were sub-adult. However, on July 29 the abrupt if temporary end of the hot, dry weather that had dominated July coincided with a collapse in the number of Mediterranean Gulls at the site. By early August none were present, although there was an intriguing reappearance of one seen on 12 July on August 16.

To put the influx in context, only one Med Gull was seen at the site during 11 visits in July 2017 and a total of only 14 on four of the nine visits made in July 2016. The site also saw increased numbers of most other gull species in July 2018 compared with July 2017, but not to the same extent as for Med Gulls.

Gulls at the Arun roost in July 2017

Species/Date	1	1	6	8	12	16	17	18	19	24	29
Med. Gull	0	0	0	0	0	0	0	0	0	1	0
Common Gull	0	0	0	0	1	0	0	0	0	0	1
L. Black-backed	0	0	0	0	0	0	0	0	0	0	1
G. Black-backed	1	0	0	1	2	0	1	1	1	0	0
Bl-headed Gull	3	0	40	7	61	63	67	152	55	130	95
Herring Gull	12	8	3	2	19	58	56	37	35	290	240

Note: Tide, weather, disturbance and time of day can lead to major differences in the number of birds present.

It is uncertain whether the 2018 influx occurred simply as part of the more general increase in the occurrence of Med Gulls on the south coast, or also reflected more localised conditions, perhaps with the dry weather pushing birds that usually pass along and stay close to the coast moving higher up the river in search of better foraging areas. Either way, not only were the numbers much increased but 22 of the gulls carried colour rings bearing unique combinations of letters and numbers, 20 of which were read with a telescope while the birds were loafing on the bank at relatively close range.

Ringed Mediterranean Gulls by the Arun: July 2018

Ring colour	Code	Ringed at:	Ringed when:	Ringed as:	Seen since (no. of times by country):	Seen by Arun:
White	3086	East Flanders, BE	30/5/08	pullus	BEx1	12/7
White	3TYR	East Flanders, BE	6/6/10	pullus	BEx2	23/7
White	E927	Antwerp, BE	23/6/12	pullus	FRx2, BEx2	18/7
White	3322	East Flanders, BE	7/6/13	pullus	BEx1	27/7
White	3NHJ	Antwerp, BE	12/5/17	3CY	BEx1	11/7
White	3YJE	Antwerp, BE	14/5/17	>3CY	FRx2	11/7, 18/7
White	3117	Antwerp, BE	10/5/18	3CY	-	11/7, 18/7
White	3NYH	North Holland, NL	24/6/16	pullus	FRx4	23/7
Green	7T8	Vendee, FR	18/6/11	pullus	FRx16, PTx3	12/7
Green	RNL0	Somme, FR	24/6/14	pullus	FRx14, SPx10, PTx1	11/7
Green	RH8P	Vendee, FR	27/6/15	pullus	FRx11	23/7
Green	RT79	Vendee, FR	1/7/17	pullus	SPx1, NLx1	11/7
Green	RL72	Vendee, FR	1/7/17	pullus	FRx1	12/7, 23/7
Green	RJR9	Vendee, FR	1/7/17	pullus	FRx3, PTx1	18/7, 23/7
Green	R3CR	Vendee, FR	1/7/17	pullus	-	26/7
Green	R9AE	Vendee, FR	1/7/17	pullus	FRx2	26/7
Green	RV7X	Vendee, FR	1/7/17	pullus	FRx4, UKx1	27/7
Red	PUP0	Z Mietkowskie, PL	30/5/17	pullus	-	12/7
Red	PUE2	Zbiornik Przykona	26/5/18	pullus	PLx1	23/7
Red	HE43	Bugyi, Pest, HU	10/6/09	pullus	UKx1, PTx1, FRx1	12/7, 16/8

Note 1: BE – Belgium, FR – France, HU – Hungary, NL – Netherlands, PL – Poland, PT – Portugal, SP – Spain. For example x2 means seen twice in a particular country since original ringing.

Two other birds had rings which couldn’t be read but were additional birds. One, a white-ringed bird in juvenile plumage, was the only such bird seen at the site. Another had a yellow ring, a colour used by ringers in Germany, the UK and Ireland, which was the only yellow ring seen at the site.

Few European gulls have received more attention from ringers than Med Gulls. In July 2018 only one other colour-ringed gull – a Herring Gull ringed at Rainham Tip, UK in January 2015 – was seen by the Arun. But even so the occurrence of more than 20 ringed Med Gulls within a few weeks is notable and, thanks to the speed with which ringing bodies in France, Belgium, Poland and Hungary responded to submission of the records, with replies received for all the 20 birds, quite a lot is known about them.

Nine of the 20 birds were ringed in France, eight at the same site in the Vendee. Indeed, six of them were ringed on the same day -- 1 July 2017. Of the rest, seven were ringed in Belgium, two in Poland, and one each in Hungary and the Netherlands. Seventeen of the total were ringed as pulli, nestling birds not yet able to fly.

Information on the 20 gulls after their initial ringing ranges widely, with the variation depending in part on how long it is since they were ringed. But that isn’t always the case. Take the bird with a white ring numbered 3086. This was ringed as a pullus in East Flanders way back in May 2008. But it wasn’t recorded again until May 2018 in Antwerp, two months prior to its appearance by the Arun on 12 July.

Contrast this lack of records with green ring 7T8. Ringed as a pullus in the Vendee in June 2011, it was recorded a further 19 times before being seen by the Arun. Sixteen of the records, including a record of attempted nesting, came from France between 2011 and 2013. After that it went missing until it was seen in Portugal in January 2015, December 2017 and January 2018.

Even better recorded is green ring RNL0. Banded as a pullus in France in June 2014, it has since been seen 25 times in western and southwestern France, northwest and southern Spain, and on Portugal’s Algarve, with Gijon in Spain one of its preferred winter sites.

Initial ringing locations and other sightings

While many of the birds were recorded solely in Western Europe -- travelling south in winter from more northerly breeding or summering grounds -- this is not the only pattern. For instance red ring PUP0 was banded as a pullus at Zalew Mietkowskie in western Poland on 30 May 2017. Just over 400 days later it was 1,199 kilometres to the west by the Arun.

It probably made the journey considerably quicker if it was like red ring PUE2, which was ringed at the artificial reservoir Zbiornik Przykona, created to serve the Adamow brown coal mine and power plant near Turek. This was ringed as a pullus on 26 May 2018 but 58 days it had travelled 1,334 km to the west at the Arun roost. And in fact the journey was quicker, because the bird was controlled at the nest site on 7 June, meaning it made the journey in under 47 days.

However, these Polish birds might now settle into a north-south pattern if they are anything like red ring HE 43. This bird was ringed as a pullus on 10 June 2009 at Bugyi some 30 km to the south of Budapest in Hungary. At some stage it moved west since on 24 July 2012 it was at Walton Reservoir, Walton-on-Thames, UK. After that its movements took on a more north-south orientation, with the bird being recorded in Portugal on 11 November 2013 and in France on 11 October 2016.

Some of the records may indicate that birds were travelling together. Two birds present together by the Arun had been ringed within three days of each other in May 2017 at the same site in Antwerp. Some of the six birds ringed as pulli on 1 July 2017 at Vendee may also have been travelling together. Indicative of this is the fact that RL72 and RJR9 were both recorded in Finistere, France in Oct 2017, albeit on different days.

The direction of travel of the birds seen by the Arun is not clear from the four cases where birds were recorded within the previous month. White ring E927 was present on 19 June in East Flanders, Belgium, RJR9 in Finistere, France on 14 June, RH8P in Vendee, France on 4 July and RV7X in Lodmoor, UK on 10 July – quite different areas that could indicate either westward or eastward movement.

Some birds clearly stayed by the Arun for several days based on repeat sightings of five birds, one of which was seen on both July 12 and July 23. However, most appear to have moved on quickly since repeated sightings were rare in spite of regular checks at the site. There was also a shift in the age composition of the birds as the month went on, with fewer adults and more birds in juvenile or sub-adult plumage. A record of one bird, HE 43, which was seen on both July 12 and August 16 may indicate either that it stayed somewhere in the general area or revisited the site after moving elsewhere and then back - it is impossible to say without other sightings.

It is interesting that none of the birds came from the south coast-based UK breeding population -- the Lodmoor bird was ringed as a pullus in France and the Walton-on-Thames bird in Hungary. In this respect, as in many others, the information gleaned from the rings may provide insights but it also raises more questions than it answers.

That said, a ring does allow a bird a history. It is often a limited and tantalising history, but one that transforms an individual record of a bird into an individual bird’s record. However, the ring only allows a history to be established if it is recorded again; otherwise its unique combination of letters and numbers is no different than the content of a burnt tome at Alexandria.