Burhou

12/13 July 2013  

The annual trip to Burhou in early/mid July to colour ring Lesser Black-backed Gull chicks is one of my most eagerly anticipated events of every year. I have now learnt that I can never assume how the colony is doing, because every year the majority of the circa 1,200 pairs of gulls lay and incubate eggs...but around the time of hatching or soon after it can go very quickly and very badly wrong! The first time I saw this was in 2008 (but such a failure is also documented for 2007), when I only found three chicks from all those nests! 2009 and 2010 were returns to much better productivity, but then again in 2011 the colony failed to produce more than a handful of chicks to fledging. Although not a bumper year for fecundity, 2012 was moderately successful...so what of the Class of 2013?!

After what seemed like a long wait (it always seems that way to me!), the date came around and I caught the Bumblebee boat service up to Alderney at 0730 on Friday 12th July. With a stiff NE breeze (force four gusting five), it was a bumpy ride. This summer the Alderney Wildlife Trust had contracted with professional local photographer Chris Bale to produce some photographs of the breeding seabirds for use in its promotional and educational activities. Chris was on the boat with me (his third attempt to secure the photos in this windy and difficult summer!).

Tim Morley (the Alderney Wildlife Trust Seabird Ecologist) was at Braye Harbour to meet us. With over an hour before our scheduled departure to Burhou, Tim and Chris went off to photograph nesting Ringed Plovers, while I settled in at Crabby Bay to obtain my first gull colour ring reads. With the strong NE winds our trip was pushed back by another hour and a half giving me a decent amount of time to secure some very valuable ring reads at Crabby. I finished with 18 Lesser Black-backed Gulls, along with three Herring Gulls, with additional Herring Gull singles at Braye Harbour and Platte Saline. An analysis of the origins of these birds is appended to this report.

At mid-day we met again at the harbour and Juan (AWT Marine Officer) brought “Sula of Braye” alongside for us to load the gear. Tim Morley and Paul Griffin (AWT Terrestrial Ecologist) were helping me to ring the chicks this year. Within 25 minutes we were rowing ashore at Burhou. It was absolutely marvellous to be back amongst the nesting Lesser Black-backed Gulls. Initially all looked well with a few chicks running around above the beach in the colony just south of the hut, and the adults calling noisily.

With concerns that time may be limited for the work, we grabbed a quick drink in the hut and then began the search for chicks. The first area searched was adjacent to the hut, and this went reasonably well with eight or ten large chicks found and ringed. However, as we moved closer to the sea we encountered two problems – firstly Paul began to suffer very badly from hay fever (not surprising given the massive quantities of pollen being released from the grass as we walked through it and of course stuck our heads in it to look for hiding chicks!). Tim was also suffering but fortunately not as badly as Paul and he stoically continued to bury his head in the vegetation searching hard and with success for chicks. Paul also bravely battled on helping with the search and recording.

The second problem was that the chicks appeared to be pretty thin on the ground. I thought this may be because the exceptional vegetation growth this year was providing even more cover for them to hide in than normal, but we were searching hard and well, and in a co-ordinated manner. There were no chicks at all near the rocky outcrops by the hut (where they are usually very easy to locate). By the time we’d finished in this sub-colony we’d only ringed 14 LBBG chicks. I had planned to leave the main colony at the west end of the island until the following morning, but as we had so much time on our first afternoon we decided to continue.

Entering the colony we found a freshly dead Lesser Black-backed Gull (no sign of predation or oiling or being hooked or caught in fishing line). The bird’s posture indicated that it may have been killed in a territorial fight with another LBBG. Turning the bird over, we saw the colour ring - Black 6.T5. This gull had been ringed as a chick on Burhou in July 2010. It fledged successfully and was recorded at Quarteira Beach in the Algarve, Portugal that October by Michael Davis. Unlike most of our young gulls it did not however stay in Iberia, it continued into Africa and was recorded on 15 February 2012 at Tanji Bird Reserve in The Gambia by Clive Barlow. To date this is the most distant migration of any Lesser Black-backed Gull ringed in the Channel Islands (a straight line distance from Burhou of more than 4,250 km!). Although it is marvellous to know that this young gull did make it all the way back to its natal colony, where it would most likely have first bred this year or more likely next, I am really disappointed that this great traveller is dead.

Working into the colony it was very quickly clear to us that all was most definitely not well. The adult birds were still mostly present in the colony, and their behaviour was territorial but there was no mobbing of us at all. This was such a stark contrast to when we had trapped a few adults in the colony in June. On that visit I experienced the most sustained aggressive behaviour I’d ever seen from Lesser Black-backed Gulls with several adults striking my head in defence of their nests. One struck me three times before I could move out of the area.

It was a massive disappointment to ring only four chicks in the main colony, which holds 700+ nests! I now had my answer – 2013 is yet another very poor year for productivity amongst Burhou’s nesting Lesser Black-backed Gulls. In the past I’ve considered weather to be the dominant factor (e.g. 2008), but after 2011 I concluded food shortage was more likely to be the main factor driving this very very low fecundity.

Only a few weeks ago I read Kees Camphuysen’s landmark doctorate thesis on aspects of the ecology of Herring and Lesser Black-backed Gulls nesting on Texel in The Netherlands. I know that it is dangerous to draw conclusions from scientific work taking place elsewhere, but there appear to be many parallels in what is happening on Burhou and Texel. This isn’t the place to expand on my theory, but I now believe that the colony on Burhou grew very rapidly from c 300 pairs to c 1,200 pairs in the early 2000’s. Certainly the colony had reached this size by 2005. This rapid population growth was very likely driven by resource availability (food)...and for our Lesser Black-backed Gulls this may well have been (and remains) fisheries discards. This growth may also have been masked to some extent by a redistribution of nesting Lesser Black-backed Gulls in the Channel Islands with birds relocating from parts of Sark to Burhou. However, with no colour ringing programme operating at the time this is speculation on my part.

Whatever, in years when for whatever reason the food resource is not available in sufficient quantities for such a large colony to feed itself and raise chicks successfully, the birds become food stressed and in these conditions we do know from studies elsewhere (Camphuysen et al), that Lesser Black-backed Gulls can then turn to cannibalism, eating both eggs and chicks from their neighbours in the colony. To make it worse too Camphuysen showed that once a pair has suffered from cannibalism from neighbours they often adopt the behaviour and eat eggs and or young from other nesting pairs. In this way a frenzy of cannibalism can wipe out the colony’s breeding effort in a short period of time. I have not seen this take place on Burhou (which is not surprising given how little time I spend in the colony), but what I have seen is the situation where all appears well right through to mid-late incubation...but then within a period of several weeks the eggs disappear and there are no (or very few) young to be found in the colony. There are no egg eating ground predators on Burhou, so the evidence on the ground (sparse though it is) would support the theory of cannibalism...but clearly more work needs to be done to establish this.

At present we do not even know for sure that the Lesser Black-backed Gull colony on Burhou is dependent on fisheries discards and offal. The position is made even more intriguing by the presence less than 30 km of Chouet landfill in Guernsey where there is a six days/week supply of rich organic food at present. This food source is certainly used by Lesser Black-backed Gulls nesting in Sark, Herm and Guernsey, but from colour ring observations it seems very little used by Burhou nesting Lesser Black-backed Gulls. One might think that nesting gulls experiencing food stress would turn to this supply of food which is so relatively accessible to them. The adult birds certainly do know all about landfill food during passage and winter periods. I have many observations of adult Lesser Black-backed Gulls nesting on Burhou from landfills in Guernsey, England, France, Spain and Portugal outside the breeding season.

It was a great shame that the pilot project this year fitting data loggers to ten of the nesting Lesser Black-backed Gulls was not more successful (birds managed to discard their loggers before retrieval). This is a project being trialled by Vicky Warwick-Evans as part of a wider PhD project with the University of Liverpool researching the potential changes in seabird (predominantly Northern Gannets and European Shags) foraging behaviour resulting from the implementation of a tidal energy project.

 

Given the problems the colony is already experiencing, and its highly uncertain future (given recent EU policy to severely restrict or eliminate fisheries discards at sea as it is such an unsustainable fisheries method), there would be considerable merit in tracking birds to their feeding grounds and establishing the facts!

A little dispirited, we left the main colony and crossed to Little Burhou. With a few European Shags still in nests (but most having fledged) the islet was quiet. Although gulls continued to hold territory (c 30 pairs LBBGs and a few Herring Gulls), we only found a couple of Herring Gull chicks to ring. Surprisingly no Great Black-backed Gull chicks were located, and despite the presence of at least three pairs on territory it is doubtful whether any nests were successful there this year.

With so few gull chicks ringed, but so much vegetation searched, we were all very tired by the end of the afternoon, so we walked back to the hut for some food and drink. I then took the opportunity to take the telescope out and try to record some colour rings. The wind was still a little breezy, but with no heat haze and superb light, observation conditions were rather good, and in a couple of hours I managed to identify 85 Lesser Black-backed Gulls and 13 Herring Gulls. What was very obvious was the number of chicks ringed in 2009 (23) or 2010 (eight) which are now back in the colony – presumably most birds trying to hold territory and prospect for their first nesting attempt back in their natal colonies next year or the year after.

A second summer Yellow-legged Gull was resting on rocks with Lesser Black-backed Gulls by the main colony as the tide rose.

After a very good night’s sleep (no doubt a result of the physical work the day before!), I rose and decided to use the wonderful early morning light to read more rings. This is important before the heat haze builds making reading so much more difficult (and impossible on distant birds). I was thrilled to record another 60 ring reads on Lesser Black-backed Gulls, along with eight on Herring Gulls. This is all excellent quality data for the long-term study of Burhou’s nesting gulls.

After this we set off to search the gull colonies by the rocky outcrops behind the hut, all the way to the beach, and then along the beach on the northern side of the islet. We ended up with another 11 Lesser Black-backed Gulls and seven Herring Gulls ringed. Although still poor in number what this showed was that of the 29 Lesser Black-backed Gull chicks found and ringed, 26 were located outside the main colony in much smaller nesting groups of gulls. While shortage of food would have still limited the numbers of chicks raised in these areas, it is tempting to speculate that the sort of frenzied mass cannibalism which may well have developed in the densely populated main colony (stripping out virtually all the eggs and chicks), did not develop in the less densely populated peripheral sub-colonies...hence the survival of a few more chicks in these areas?

With time on our hands we completed the work at the eastern end of the islet, where we found the only Great Black-backed Gull fledgling of the entire trip, along with another Lesser Black-backed Gull chick and Herring Gull chick.

The final ringing tally of chicks ringed for the whole island search in 2013 was 29 Lesser Black-backed Gulls, 11 Herring Gulls and a single Great Black-backed Gull. It is hard to see how a colony of 1,200 pairs of Lesser Black-backed Gulls can maintain its population with such poor recruitment into the population, especially as it is known that 2013 was not an exceptional year (2007, 2008 and 2011 were similar or even worse!).

Although numbers are tiny...the news for Herring Gulls was a little better this year. In 2012 only five nests were recorded pan-island for this species, but in 2013 at least 18 nests were located and productivity wasn’t too bad. A tiny indicator perhaps that Herring Gulls are largely dependent on different food sources in the breeding season from Lesser Black-backed Gulls on Burhou. I have more colour ringing evidence for Burhou nesting Herring Gulls using Chouet landfill in Guernsey as a food resource.

Tim used some of the time we had on Burhou to count the Puffin rafts – reaching a maximum of 262 birds during an evening count. Puffin numbers appear to have held up well on Burhou again this year, and the previous week the Alderney Wildlife Trust had captured rare film footage of a Puffling successfully leaving its burrow and fledging (https://vimeo.com/70105987 & https://vimeo.com/70039947 – a wonderful reward for all the hard work put in by AWT and its hard working staff. The inspiring work of the Trust can be followed on https://www.facebook.com/LivingIslandsLive).

Juan arrived on cue to pick us up shortly before 4 pm on Saturday 13 July. The sea was like a mill pond, as smooth as a billiard table. We enjoyed the Puffins rafting in the bay in front of the hut, and then set course back to Braye Harbour. Krys Page was on board too, and she very kindly opened up her Little Rock Café to feed the Burhou contingent with the most wonderful burritos – enjoyed all the more for the slight hardships of an overnight stay on Burhou!

On this trip – even more than usual – I was able to spend a little time simply watching the gulls and their interactions...and marvel at their striking beauty, their raw energy and their charisma – for me there really is no better icon of island life than gulls in general, and I consider myself massively privileged to be able to enjoy studying them. Some of this beauty was captured on this visit by photographer Chris Bale. Chris has endless patience to hide away immobile in full camouflage gear for hours on end to try to obtain shots of birds behaving naturally. His results speak for themselves! Below are a few of his photos of Lesser Black-backed Gulls – some of the best I’ve ever seen anywhere. You can enjoy some more of Chris’ work on his Facebook page or on his web site (links below).

In science negative results are often as valuable as positive ones, and I know that our work on Burhou in 2013 has discovered another important piece in the jigsaw puzzle to try to work out what is happening with important seabirds colonies in the Channel Islands – in this case the Lesser Black-backed Gulls, but I can’t help feeling disappointment over the colony’s lack of success again this year...and the fact that it is now going to be a very long wait until next season...when again the big question will be – How many chicks will be recruited into the population to give this wonderful colony a decent chance of a strong survival into the future?

 

 

PKV

14 July 2013