Saturday, 27 August 2011

Non-stop work, visitors, changeover of field assistants and a dead laptop are all to blame for the lack of recent updates...apologies! The first chick hatched on the 23rd of July and, since then, there’s been 2 or 3 new hatches most days, which has meant we've been busy, busy, busy. A total of 58 chicks have hatched over the last 4 weeks. Given the abysmal breeding season experienced by most of Shetland’s other seabirds, we were prepared for a poor season for the Stormies too. While Storm Petrels are generally more resilient, since they can travel much further to forage and feed lower in the food chain, the indication from other seabirds was that environmental conditions must be especially bad this year. Early indications from the Stormies were not great with some chicks being left unattended at only 2 or 3 days old, by which time they may not be capable of thermoregulating and need the warmth of a brooding parent to maintain their body temperature. By 10th August, 8 out of 34 chicks hatched so far had died. That’s almost a quarter and a far lower survival rate than in 2010!


A healthy, well-growing chick, aged ~25 days

Prospects have looked a little brighter in the last couple of weeks, with parents brooding chicks for longer and we haven’t seen any limp and lifeless-looking chicks which seemed to be a recurring theme. The need to replenish body reserves and bring back sufficient food for their chick may have forced parents to leave a young chick unattended. It is expected that later hatching nests have a lower survival rate, since these later breeding birds are usually young inexperienced birds; so, it seems interesting that in fact survival seems to be improving. Perhaps the mild ‘summer’ weather that has finally arrived in Shetland over the last week has made life easier for those birds whose young have hatched just recently. However, there are still many chicks less than 10 days old, so we wait to see how many survive this most critical period of life...


A young chick, aged ~10 days

Friday, 15 July 2011

Laying down the foundations

Almost 70% of monitored nests are now occupied by a breeding pair. In 17 nests, the egg is being incubated in a nest-cup holding a temperature logger, so hopefully some valuable data on frequency of occurrence of egg neglect (breaks in incubation) are being recorded. One of these eggs has, however, been abandoned already and kicked out of the nest (see below). Another 10 nests have been occupied on a handful of occasions over the season, so there may be a few more pairs yet to lay an egg. It may seem late, but, last year, the last egg was recorded on 2nd August.

An abandoned egg, kicked out of the nest-cup. You can see a temperature logger (an 'i-button') in the centre of the photo for recording nest temperature to monitor egg neglect.

A handful of nests that fledged chicks last year have not been occupied at all during the day so far, leading me to assume that those birds are probably not going to breed this year. However, birds do not always occupy the nest during the daytime prior to laying, so there may be a few unexpected surprises yet. Daytime occupation of nests seems highly variable – typically, one or two birds might occupy the nest on two or three days over the course of maybe 3 weeks prior to laying. At one extreme, one or two birds of a pair were present on 8 occasions over the course of a month before laying an egg. Yet, other nests are checked every day and, day after day, recorded as ‘empty’, then all of a sudden, one day, I’ll find a bird sat there on an egg!

A pair of Storm Petrels occupying a nest-box during the day. This nest-box has not been used for breeding before, so these birds are probably young birds that may be about to breed for the first time...watch this space...

While Storm Petrels are still laying their eggs, most other seabirds are much further ahead in their breeding season. Of the few Shags (Phalocrocorax aristotelis), Guillemots (Uria aalge) and Razorbills (Alca torca) that have successfully bred this year, most of the young have fledged and left the cliffs. Gull (Larus spp.) chicks are almost fully-feathered (see below) and must be close to fledging. Related to the Storm Petrels, Fulmars (Fulmarus glacialis) also have a lengthy pre-natal development, but breed earlier than Storm Petrels. I’ve noticed the first few Fulmar chicks over the last week, but all still being brooded by a parent, so probably less only a week or two old; a tuft of pale grey downy fluff poking out from underneath an adult usually gives their presence away.

Great Black-backed Gull chick playing the ‘If I can’t see you, you can’t see me’ game

It was such a pleasant day on Mousa yesterday that I took my time ambling around the island, checking nests at a leisurely pace, and keeping my eyes open for anything of interest...I was praying for some Orcas to start leaping out of the flat-calm, shimmering, blue ocean. Passing through areas used by nesting Bonxies (or Great Skuas, Stercorarius skua), I was scanning the ground ahead for any fleeting glimpses of a chick scuffling away - the most I usually see of a Bonxie chick. However, today, I had close-up encounters with two chicks (belonging to different pairs), both of which were almost misfortunate enough to have my foot land on top of them! Frozen to the ground, not moving a muscle, and hunkered down in the long grass, I didn’t see either of them until I almost stepped on them. Each time, I stopped with a start and looked down to see a pair of large black eyes surrounded by golden fluffy down staring back up at me...
A Bonxie chick hunkered down in the long grass. It must be a few weeks’ old, as you can see a lot of the feathers growing in on the back and wings (though apologies for a bad photo taken on my phone!).

Tuesday, 5 July 2011

It's gonna be a cold lonely summer

A key characteristic of the eggs of Procellariiformes (or ‘tubenoses’) – the group of birds that includes storm petrels, shearwaters, albatrosses, petrels and fulmars – is the ability to withstand chilling (i.e. periods without being incubated). Such neglect is unlikely to be tolerated by rapidly-developing embryos, but the slow rate development of Storm Petrel embryos probably makes them less vulnerable to lapses in incubation. This characteristic is probably an adaptation to a lifestyle that involves foraging at such great distances from the breeding colony on unpredictable food resources. Severe weather or food shortages may prevent the off-duty bird from returning before the incubating bird has to leave to replenish its own body reserves. Incubation places a huge energy demand on parents and Storm Petrels undertake long incubation shifts of 2 or 3 days, during which they do not feed. Additionally, since they are restricted to entering and leaving the nest during darkness (due to the risk of predation), if the off-duty bird hasn’t returned by the time the sun is almost rising, the incubating bird may be left with the choice of leaving now or waiting another 24 hours. 

 

A ‘cold’ (unincubated) egg


In 2010, egg neglect was recorded in 38% of nests, from regular visual inspections of nests to see if an adult bird was present or not. Eggs that endured chilling of up to 12% of the total incubation period still managed to hatch successfully and 70% of those chicks successfully fledged. Neglect resulted in the lengthening of the incubation period by up to about 5 days. It would be desirable to develop a means of monitoring egg neglect that didn’t involve the high labour of checking nests regularly throughout a long incubation period (at least 39 days) and does not involve the intrusion of shining a torch in nests every day. It is hoped that this can be achieved remotely with the use of temperature loggers. I-buttons are the size of a large watch battery and record temperature (as frequently as you like) and store the readings in an internal memory. The i-buttons have to then be retrieved to download the readings.


An i-button which records temperature at intervals of your choice up to a maximum of 1048 readings

It may be relatively straight-forward deploying i-buttons in the nests of ground-nesting birds, which are readily accessible and have an obvious nest-cup (where the egg(s) are laid), but it is rather more of a challenge when it comes to Storm Petrels. The cavities and crevices that they nest in are, more often than not, out of sight, let alone within reach. Those that are accessible generally involve squeezing and manipulating your hand and arm through the maze of cavities within the dry-stone walls (or ‘dykes’ as they’re known in Shetland) and relying on your sense of touch, rather than sight. The many bruises and scrapes we have endured are evidence of this. In addition, it is often not obvious where a pair is likely to lay their egg. Storm Petrels don’t build much of a nest; at the very most, there may be a slight depression, which may be lined with a bit of dead grass. A logger can only be deployed if the substrate is soft mud, within which it can be sunk into, such that it is level with the surface; if it were to protrude from the surface, a fragile egg could be knocked against it and broken.


Struggling to access a nest-cavity and deploy a temperature logger within the nest-cup

If a bird is incubating an egg over a temperature logger, it is anticipated that the temperature logger will record a higher temperature than ambient temperature. However, Storm Petrels incubate their eggs at a fairly low temperature – a lot lower than most other birds – which is probably an adaptation to enable them to endure such long incubation shifts without feeding and explains the slow development of embryos. Consequently, to confirm the presence or absence of a bird, a second temperature logger is deployed within the nest, but outside of the nest-depression. When temperature loggers are retrieved, once a chick is hatched (or an egg has been abandoned), we will be looking for a difference in temperature between the two loggers.

It is hoped that this remote means of monitoring egg neglect will provide an absolute measure of neglect for the entire period of incubation, without the need for somebody to check nests every day and without causing any disturbance to breeding birds. Fingers crossed it works!


Thursday, 23 June 2011

A storming success (hopefully!)

Just in the last week, the numbers of Storm Petrels present in the colony has noticeably increased. This has also coincided with some fairer and calmer weather, making fieldwork more enjoyable and enabling more people to come out to Mousa and enjoy the spectacle of watching the Storm Petrels returning to the colony as darkness falls. Mousa Boat Trips (www.mousa.co.uk) operate two night trips every week between late May and late July, bringing people over to witness this display. Few trips have actually run so far this year, however, due to the relentless strong winds making Mousa Sound impassable.

The Mousa Ferry, which offers daytime and night trips to Mousa during the summer months, at the pier in the West Ham

Due to their small size and subsequent vulnerability to predation, all aerial activity at the colony occurs during darkness. Birds start to arrive about 30 minutes after sunset and, by the time the sun has fully risen, no birds are left to be seen, having either departed to feed far out to sea or tucked themselves up safe in their nesting cavity. At this time of year – midsummer – at 60˚ north, this offers a very narrow window for activity. Birds return to the colony from mid May onwards to re-establish their territory and bond with their mate. Year after year, birds return to exactly the same nest-site to breed with the same mate. Those fortunate enough to visit a Storm Petrel colony at night can observe aerial courtship displays and hear birds furiously singing from their nest-sites.


The 'Simmer Dim' - as dark as it gets in Shetland at midsummer

Saturday’s visitors witnessed a spectacular display of numerous Storm Petrels whizzing around the exterior of Mousa’s Iron Age Broch. This phenomenal structure is at least 2000 years old and it’s 2-metre-thick stone walls offer a maze of cavities and crevices for Storm Petrels to breed in. Flash photography is not allowed, to avoid disturbance to this internationally-important colony, which is recognised and protected under European law; consequently, I can’t show you any images of this spectacle, you’ll just have to come and see it for yourself one day.






Mousa Broch and the boulder beach, home to thousands of breeding Storm Petrels lit up by a full moon. On lighter nights like this, birds tend to return to the colony a little later than on darker, cloudier nights.

Prior to laying, birds regularly visit their nest-site at night and occasionally occupy the site during the day. In late May, daytime inspections of nests revealed attendance at a maximum of 5 nests out of almost 90 that were monitored in 2010. Gradually, occupancy has increased, with a peak (so far) of 31 nest-sites occupied yesterday. The first egg was recorded on 10th June – exactly the same day as the first egg was recorded last year. As of today, 17 pairs have laid an egg. Most of these birds have just laid within the last 5 days. Visibility inside nests is typically limited – one of many challenges of studying a bird that’s only active within the colony during darkness and nests in cavities out of site! Consequently, the egg is often never seen and laying is only confirmed by the presence of a bird on 3 consecutive days. The breeding period is greatly protracted in Storm Petrels; last year the first egg was recorded on 10th June and the last on 2nd August! Previous research in the late 1960s by Derek Scott on Skokholm revealed that it is the experienced birds that lay earlier in the season and the newly-formed pairs and inexperienced birds that lay later on.

Despite the poor season for Shetland's other seabirds, let's hope 2011 brings better fortunes for the Storm Petrels. See the RSPB's latest press release reporting the success of the Mousa colony at http://www.rspb.org.uk/news/282636-storming-success-for-storm-petrel-colony?utm_source=rss&utm_medium=feed&utm_campaign=News

Wednesday, 8 June 2011

Back to basics

Relentless force 6-7 south-westerly winds have not helped the 2011 field season get off to an easy start. Stuck on mainland Shetland for the first 10 days or so after arriving, the forced imprisonment in a caravan at least provided plenty of time to crunch data (groan). The hammering of the rain on the roof and the unsettling rocking of the caravan, however, was not particularly comforting or conducive to focusing on statistics. Terrified that the caravan and I might be blown to Norway at any given moment, I breathed a sigh of relief when the wind eventually abated...though only just for long enough for us to get ourselves to Mousa and settle into some more stable accommodation, albeit not very water-tight!



The Mousa bothy...home sweet home

Needless to say, the bothy needed a bit of a clean and tidy following the accumulation of a winter’s worth of dust and grime and having been providing shelter to wheelbarrows, sheep-shearing gear, fencing etc. It soon felt like home again, though we’ve already spent more time than desirable being enclosed by its four dull, grey, windowless (well, there is just one small window) walls. I would say it could only get better, apart from after only a couple of days off Mousa, we already find ourselves once again stuck on the mainland.





Spring-cleaning of the bothy

In between the showers, we’ve been blown around Mousa for the last two weeks, trying to relocate nests which were monitored last year...not so easy when one boulder looks much like any other. Automated cameras and motion sensors have been re-installed to continue monitoring visitor pressure in different areas of Storm Petrel nesting habitat around the island. On our first full day back (26th May), we checked 47 nests and found 6 of them were occupied by birds. The birds haven’t laid an egg yet, but daytime occupancy suggests these will be early breeders. Last year, I recorded the first egg on 10th June, so, any day now, we might see our first egg. The fortunes of Shetland’s other seabirds this season are not looking too rosy. Gales and large swells have washed out many Guillemot nests at Sumburgh Head, the Arctic Terns (tirricks) at Grutness don’t seem to be doing anything, and even the Bonxies aren’t numbering as many as last year. Fingers crossed, the season holds more promise for the Storm Petrels. The fact that Storm Petrels feed lower in the food chain than other seabirds (mainly feeding on plankton) and can forage at such great distances from the colony, might be expected to make them more resilient to locally-unfavourable environmental conditions. The story will slowly (remember Storm Petrels incubate their eggs for 40 days and rear their chicks for about 60 days!) unfold over the course of the next few months...

Wednesday, 18 May 2011

Where did the winter go?

It seems just like yesterday that I was on Mousa, weighing and ringing Storm Petrel chicks as they grew closer to fledging. Seven months, however, have sailed by since then and here I am, back in Shetland, hiding inside from the wind and the rain and about to embark on a second season of fieldwork for a 4-year study on the effects of environmental change on the breeding behaviour and physiology of the European Storm-petrel. Out of 69 breeding pairs that were monitored in 2010, 42 pairs (60.9%) successfully fledged a chick. Let’s hope for a equally good season this year!


Despite the current weather, I remain optimistic for a fairer summer than last year. A trip back to Shetland just 2 months ago reminded me what cold weather really feels like. I witnessed all 4 seasons in 3 days – I arrived to a decent snowfall, force 7 winds, and wild seas, while the next brought blue skies and sunshine, while the ocean was flat calm. Before I knew it, however, the sun had vanished, the temperature was just pushing 2˚C and horizontal sleet was pounding on my back. I couldn’t have asked for anything more or less.

Sumburgh Head under a light dusting of snow

The main purpose of the trip was to interview and recruit fieldworkers for the 2011 season, though it happened to also coincide with the South Mainland Up Helly Aa – an annual festival to celebrate Shetland's heritage (see http://www.uphellyaa.org/ and http://www.smuha.org/ for more info).  I was staying with Helen, the RSPB South Shetland warden, who roped me into helping on the bar for the evening celebrations. I quickly reminded myself how to pull a pint and use a till (it had been a good while), before being thrown straight into the frenzied celebrations and surrounded by Irish Leprechauns, peas in a pod, alpacas, pirates, penguins, among many other inspired costumes.

The torch-lit procession heading down from Sumburgh Quarry towards Grutness Beach

There were Flintstones, penguins, pirates, peas in a pod..and many, many more


The procession culminates in the burning of a galley

As if that wasn’t enough of a treat, the following morning brought even more delights...after clambering into bed at 5:40, Helen and I initially weren’t enthralled to be woken at 11am by the ‘phone ringing. However, our attitudes quickly changed when we found out there were 3 Orcas heading south and in our direction. Rather bleary-eyed, we headed straight to Grutness, where I picked up at least 2 Orcas just offshore. Racing up to Laaward Point, we enjoyed good views of what turned out to be two pods, each of 3 animals. Having been promised sightings of Orcas from Mousa last summer, the only day they were seen in Mousa Sound, I was collecting someone from the airport! Let's hope for more sightings this summer!

Orcas off Laaward Point, March 2011