Alistair Baxter is completing a PhD investigating the reasons behind Dotterel declines in Scotland. Read on to find out more about his exciting work...
Dotterel declines in Scotland: Out of sight out of mind?
Over the last thirty years, National Surveys led by the RSPB and Scottish Natural Heritage (SNH) have revealed dramatic declines in dotterel numbers across the UK. The most marked results have been the total disappearance of breeding dotterel from England, Wales, and many previously good breeding sites in Scotland. I am undertaking a PhD, aimed at identifying the factors leading to dotterel declines in Scotland over the last thirty years. It is easy to ignore bird species we rarely see or that are difficult to study, but I hope my work can shed some light on the reasons for declines in the dotterel and other montane bird species suffering a similar fate. Hopefully this project will be the catalyst to increasing interest and research in the uplands and I hope you enjoy reading about my experiences with dotterel and other montane bird species along the way.
Female dotterel singing on an early Cairngorm's morning.
Here’s a bit of background on all things dotterel (Charadrius morinellus for those who collect fancy Latin names). Dotterel are extremely charismatic migratory plovers (wading birds) not much bigger than a blackbird. They arrive into the UK in late March-early April from North Africa having spent the winter months basking in the Atlas Mountains and gorging themselves in preparation for their strenuous summer schedule. Some of these birds will choose to settle and breed in montane areas of Scotland, however; the main bulk will pass through the UK onto the main European breeding grounds in Norway. Dotterel can be seen on passage, most notably on several sites in East Anglia. Unfortunately, for those of you with memories long enough to recall commonly sighting large flocks (‘trips’), these occurrences are now few and far between; with dotterel declines in Norway thought to be at least as severe as those recorded in the UK.
Very snowy Cairngorms welcome the start of the field season.
After arriving in Scotland, dotterel head for mountain plateaus above 700m in altitude where they are to be found breeding until mid-August. Whatever the reasons for dotterel choosing to breed and spend their summers in some of the most inhospitable areas of the UK, this provides a researcher and outdoor enthusiast with the mouth-watering opportunity to carry out fieldwork in some truly breathtaking mountain surroundings!
A nice bright female dotterel.
The first fieldwork day dawned early and, through my inexperienced eyes, it was far too cold, misty, and ‘dreich’ for fieldwork....apparently not! I would soon find out this is actually an above average summer’s day on the Scottish tops. Unperturbed, James Gordon (my RSPB Research Assistant), Dr. Steven Ewing (RSPB supervisor), and I headed up one of the study sites I would be collecting the bulk of my data and intensively surveying over the next three field seasons. Predictably, having spent the previous month carrying out capercaillie surveys for the RSPB, James set the pace and as I puffed, cursed, and panted behind him I began to realise why the montane regions of Scotland remain so under-studied. However, as we emerged over the last rise, we were surrounded by mist and stood on a dense moss carpet which blanketed much of the summit plateau the effort became totally worthwhile and I felt privileged to have the chance to spend so much time in such a place.
With dotterel habitat use and habitat changes the particular focus of this first year, we spent most of the day on hands and knees rooting around in moss and heather and discussing teething issues with what I thought I’d so elegantly (if not slightly optimistically) planned in my office in Aberdeen. The following inevitable scaling back of my grand plans also seemed a feature of the first few days as the realisation of scale in mountain fieldwork became apparent. Despite all the changes in plans, still revelling at the possibility of effectively living in the mountains for the next four months I felt it had been an incredibly productive first day. There was however still time to see the bird I’d be studying for the next three years and a distinctive metallic “peep” had us all scanning the horizon. A bright female stood seemingly unafraid only 40m away. Partly because of their tame nature (defence mechanism to draw predators away from eggs/chicks), the gaelic name for dotterel is 'amadan-mòintich' meaning ‘fool of the moor’; presumably due the ease with which they could be caught/hunted. Despite this, dotterel can in fact be incredibly inconspicuous and not least when incubating eggs; you can walk within a metre of some incubating males and be none the wiser. It is fortunate the Scottish summer days are so long as locating dotterel, let alone incubating male dotterel, can be a time consuming and patience testing business. I have of course been lucky enough to see dotterel almost every day since and as a result of the obligatory eight to ten miles walk each day and five Munros (3000ft hills) a week the fieldwork has thankfully got a lot easier.
Incubating male dotterel- notice how dull it is compared with the female in the first photo.
Much of this year’s fieldwork is repeating ecology studies carried out during the 1980s by SNH. By re-assessing habitat availability, habitat quality, and invertebrate abundance we hope to see if changes in these factors have caused the declines in dotterel numbers since the 1980s. Even after a difficult start to this season, with huge amounts of snow and sub-zero temperatures in May, the dotterel have begun to breed (better late than never!) and we are currently monitoring 11 nests across three sites. We focus nest searching on areas where only single male dotterel are present as this is taken as strong evidence of breeding. Unusually for a bird species it is only the males that incubate chicks. In fact, although on some sites females will contribute to incubating eggs there are no published records of females helping to rear chicks and they will usually leave the male about a day after laying the whole clutch of speckled brown eggs.
Male dotterel brooding three chicks.
Over the last three days we have had the first chicks of the season hatch and it seems all the nest finding effort early in the season is coming to fruition. The mountains seem thriving with life at the moment and I’ve found it amazing to see how the tops change over the dotterel breeding season, with dull grey moss turning to the deep pinky red of bilberry and the rich green of three-leaved rush. The birds are also at their noisiest and most vibrant at this time of year, with chicks of Golden plover, dunlin, and ptarmigan well on their way to fledging, parents are busy feeding hungry mouths and warding off those who get too close.
A “loafing” Ptarmigan – I’ve never seen a bird species that spends so much time sitting down!
I hope you’ve enjoyed reading my first instalment of this blog and I’ll bring you an update of how the remainder of this first field season panned out in August. Until then, keep your fingers crossed the stay at home dotterel dads are working as hard as we are, if so we’ll soon have juvenile dotterel on the wing and preparing for the long migration South!
All photos by Alistair Baxter.
Indeed, I think Tipulids make up a substantial amount of Snow Bunting diet. The 2011 Snow Bunting National Survey (tied in with the Dotterel survey) results will also be released at some point I expect. I’m not at liberty to discuss this work really though as it isn’t my project. However, changes in snow lie patterns and their effects on both Dotterel and Snow Bunting is something we’re looking into. Unfortunately it’s impossible can’t say whether it’s an “emergence year” or not. Tipulid emergences are not synchronised between sites, so an emergence year on one hill is not necessarily an emergence year on a neighbouring hill. Tipulid larvae and adults both seem to experience mass mortality around some late snow beds with Meadow Pipits, Dotterel, and Snow Bunting all seeming to spend time feeding around these areas. It is likely Tipulids are a pretty important, easily accessible, readily digestible food source to most montane bird species. However, with emergences occurring for only a fairly short period of time (during late June-July, synchronised to the Dotterel chick rearing period) and differing by orders of magnitude in abundance between sites, Tipulids are very hard to sample at a large number of sites. This is however something I’m hoping to get my head round also.
Thank you for your comprehensive update - fascinating variety of factors possibly interacting here. I will read future updates with great interest as the dotterel is one of my favourite species and one that I have been fortunate enough to have spent time watching over the years, both in Scotland and Norway.
I think your comments on the biennial cranefly hatch are very interesting and will keep an eye out for their abundance next year - is it likely to be an emergence season? I recall chatting to a scientist studying cranefly on an east Grampian plateau where the birds were regular breeders, but where I saw none (dotterel) this year. I did see a flock of common gulls feasting on what I presumed were insects on a snowfield on this site this year, but didn't investigate which insect species they might be.
As an aside, I wonder if Tipula montana also form a significant element of the snow buntings' diet? My sense is that the snow buntings' abundance in the core Cairngorms area hasn't changed much over the last 30 or so years, but that is gut feeling not scientific observation. Has anyone been tracking that as well? It would be very revealing if snow bunting numbers/density and distribution had mirrored those of the dotterel over the period.
Apologies for the delay. I have been very busy post field season and was unaware of your comments. Here’s the best answers I have at present to your questions so far:
I have seen the paper from Beinn a’Bhuird, an interesting read but still only a solitary site. As you say, we have always known Dotterel numbers to fluctuate greatly from year-to-year but not fully understood why. However, following 3 years of surveying (2011 National Survey and resurveys of ~40 sites in 2012 and 2013), estimates for re-surveyed sites have been fairly constant over this period so we can expect the 2011 National Survey to be at least representative of this time period.
The RSPB survey paper has taken a while longer than expected as it was decided to include the 2012 and 2013 re-survey data as supportive evidence of the validity of the 2011 National Survey ie. To show it isn’t a one year snapshot in time. In addition, some further analyses of the 2011 distribution data will be included. So, when it is available in a couple of months it will be a more fleshed out paper than simply presenting survey numbers as originally planned.
In short, declines have blanketed all sites with decline across Scotland. The patterns of range contractions do seem to support climate change theory with uphill movement of the species range with many lower altitude sites disappearing completely. This is complicated by the fact that the largest site populations tend to be at both the largest sites and at the highest altitudes (and vice versa). Many small sites have been lost completely but in terms of percentage declines, many large sites have seen larger declines between 1987 and 2011 i.e. no large sites have show stable or increasing numbers. Dotterel appear to also have become more fragmented during this period. Fragmentation of Dotterel sites may contribute further to Scottish declines, i.e. with the chance of passage birds finding a mate being slimmer they may simply continue on to Norway.
In terms of my opinions on declines, having spent time on the tops with my research assistant (who was involved in survey work in the 1990s), it seems habitat hasn’t changed greatly at the four intensive study sites I currently work at. There still seems to be plenty of what we would class as ‘good Dotterel habitat’ even in many sites where Dotterel have massively declined or disappeared completely. However, this is based on fairly broad vegetation classification schemes and may not represent the details that actually matter to Dotterel.
We know grazing causes vegetation change in the montane zone by trampling and introduction of nutrients into this nutrient poor system. This is a very complicated process but basically facilitates invasion by graminoids (grasses, sedges, and rushes) into the system and reducing montane specialist species, such as Racomitrium lanuginosum, which Dotterel are known to closely associate with. I direct you to work by Rene van der Wal if you are interested further in this process. Again, this is a difficult question to answer with only poor regional records of grazing numbers kept and exact movements not tracked. I am carrying out some analysis of potential wider drivers of change I hope will shed some light on this which should inform some of the analyses investigating the mechanistic basis of declines.
with vegetation change quite a slow process it may be more likely that changes in food availability are driving declines. I carried out intensive invertebrate sampling this year which I will compare with results from the Montane Plateaux Ecology Project. This will have a particular focus on Tipula montana, a biennially emerging cranefly species that Dotterel are thought to show particular associations with. This species is cold adapted (as many montane species are) and thus thought to be highly sensitive to climate change. It was also previously seen in vast numbers across the Cairngorm plateau during emergence years but anecdotal evidence suggests emergences have got substantially smaller. A recent study from the uplands (Brooks et al 2012 from The Environmental Change Network) has shown severe declines in Carabid spp. which may be indicative of wider declines in other invertebrate taxa. I would therefore be unsurprised if similar/more severe trends are found in the montane invertebrate species.
Due to reductions in persecution there are indeed many more Ravens around on the high tops. However, by 1999 only 19% of Dotterel sites were occupied by Ravens (although this will be a slight underestimate) so they are unlikely to have contributed greatly to initial declines. I will however be looking further at this as Raven predation may have been a far greater issue over the last 14 years. I can’t be sure about other predators on the high tops but talking to the longer term surveyors’ sightings of red fox and other mammalian predators are very rare.
Thank you for your interest in this work. I hope this goes some way to answering some of your questions.
Starting to give up hope of ever receiving a reply here, seeing the promised paper or your blog update. Can you give us some sort of progress report on the latter two please?
Guess you will have seen the Scottish Birds' paper on dotterel numbers on Beinn-a-Bhuird in the September issue?
Looks as though the numbers there, in one of the core areas, are holding up well, albeit with the usual annual fluctuations that we now know are characteristic of Scotland's dotterel populations.
I would be intrigued to know what you think causes such fluctuations, and how accurate you think national survey estimates are, given such oscillations in dotterel numbers at regularly surveyed sites.
Just seen the 2011 RBBP report in BB. It states that the 2011 survey estimated a total 423 breeding males, a 43% decline from the 747 estimated by the 1999 survey, and that the rate of site occupancy had declined from 33% to 17%.
A couple of questions if I may - has the habitat changed significantly on the deserted/less well populated sites, say through overgrazing or climate-change induced vegetative changes. Has there been a drastic reduction in invertebrate populations on such sites since 1999? Are there now more nest and chick predators roaming the high tops, as I observed this year on 2 of 3 sites visited? Finally, is the decline as severe (43%) in Norwegian dotterel populations?
Looking forward to your next blog posting.
Sad to hear that some hills with once thriving populations are now almost entirely deserted. This was certainly the impression I gained during brief visits to some of the tops this year. Is this decline at the periphery on the outlying hills or in the core areas? Is it altitude or latitude related eg the lower nesting, marginal or southernmost groups? Are we heading back towards the dotterel-lean years of the mid-20th century and so on. Lots of questions that I hope the paper addresses.
In the meantime, it is good to hear that breeding productivity at the largest site was good - what is the minimum breeding productivity per pair required to maintain the population at a stable (ie not declining) level?
Looking forward to the paper, and your blog, in due course.
Thanks for your interest in my work. The field season has now come to a close so I will be writing another blog update of the work I have done in the latter half of the season so please look out for this too.
In terms of population trends from the most recent National Survey, keep an eye out for an upcoming paper from the research section headed by Mark Eaton at RSPB. This paper will publish the results of the 2011 National Dotterel Survey and put these in context with previous surveys. Until this comes out I am only really at liberty to say that there are unfortunately continued declines across Scotland since the 1999 National Survey.
It really has been quite striking to be on some hills which until relatively recently have been crawling with Dotterel but that now are almost entirely deserted. However, on a much brighter note, in terms of this year, it has been a very successful breeding season for Dotterel. Despite the early snowfall that we had in May, which didn't seem to perturb the Dotterel from laying, the stunning weather has meant breeding success at all the intensively monitored sites has been high. In fact, every nest and brood found and monitored at the largest site produced at least one fledgling.
Apologies I can't answer your question on population trends more thoroughly. As I say, wait for the paper which I believe is coming soon.
Only just seen this interesting blog Alistair. I have also spent a few days on the high tops this year and noticed an absence of dotterel where they were hitherto relatively abundant. Couldn't also help notice that there were family parties of ravens frequenting and systematically working 2 of the 3 upland areas visited. Correspondence with another montane bird expert revealed that ravens were now an almost permanent presence on one of the eastern grampian areas in question during May-July. Ravens are of course significant predators of eggs and chicks.
What is the estimated magnitude of the decline? I recall that Nethersole-Thompson estimated a total of 64-95 pairs in Scotland during the period 1945-1969 but that this was dramatically revised upwards to around 8-900 pairs I think, following the 1980s SNH study you refer to. What is the current population estimate, and does the latest BTO Atlas work support a dramatic decline over the last 30 years?