January to June 2019

blog CU postOne or two WaderTales blogs are published each month. The series is UK-based with a global reach. Suggestions of newly-published research on waders that might be of interest to birdwatchers who appreciate waders/shorebirds are welcomed. I am particularly keen to give feedback to colour-ring readers; they provide a huge amount of information that lies at the heart of these stories.

Click on a link in bold to read an individual blog.

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GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

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Winter territories of Green Sandpipers

Winter is a very different prospect for a Green Sandpiper that spends the non-breeding season in England, rather than Spain, Portugal or countries in northern Africa. Are British winterers living life ‘on the edge’ and how do they cope? One way is to defend resources within clearly-defined territories.

Life in Hertfordshire

blog2 preenKen Smith, Mike Reed and Barry Trevis have been studying a colour-ringed population of Green Sandpipers in Hertfordshire (an English county just north of London) since 1983. The focal point of their activities is Lemsford Spring, a Hertfordshire & Middlesex Wildlife Trust nature reserve. The site is  a set of disused watercress beds that provide plenty of freshwater shrimp (Gammarus pulex) in shallow lagoons fed by freshwater springs. Over the years they have been able to use their colour-ringed birds to study return rates from year to year, behaviour and local habitat use. Using radio-tags they have looked at nocturnal activity patterns and more recently they have been using GPS geolocators to find where their birds go to breed.

blog2 movementsThe highest numbers of Green Sandpipers in southern England occur in late summer, when many passage birds pass through the country, but a few birds stay for the whole winter. The Lemsford studies show that colour-ringed birds have a high return rate from one winter to the next. These birds are actually in the general area of Lemsford for most of the year, only leaving to breed for two or three months. Upon return, in late summer, they use other local sites such as gravel pits, only switching to the watercress beds in the autumn.

Individuals birds visit a suite of sites; by tracking birds wearing radio tags, the team were able to establish that even birds that fed at Lemsford Springs (below) during the daytime would roost communally at the local gravel pits overnight.

blog2 springs

Effects of cold weather

The research team found that the patterns of behaviour of the Hertfordshire Green Sandpipers varied with local weather conditions. During extremely cold weather in January and February the birds switched to roosting overnight at the watercress beds, where they could also feed. In these conditions, with the water frozen at gravel pits, roost sites were accessible to predators. Automated monitoring of tag locations showed that birds were active for around 80% of each daytime period at all times of year. Nocturnal activity varied from around 16% in autumn to over 40% in cold conditions in midwinter. This suggests that a low level of night time activity is normal in Green Sandpipers and that higher levels, found during extremely cold winter conditions, are the result of birds attempting to increase their daily food intake.

Annual survival

The return-rate of colour-ringed birds can be used as a surrogate for survival rates, bearing in mind that any bird that changes its wintering area will reduce the apparent survival rate, although still alive. (See WaderTales blog on measuring survival rates based on review paper in IBIS)

blog2 gravelOnce established in the Hertfordshire area, individual Green Sandpipers were likely to turn up in subsequent  winters, with little difference in return-rates between young birds, ringed in their first winter, and adults. There was considerable variation from year to year, with the return rates varying from 68.7 to 100%; the lowest being between 1986/87 and 1987/88, when another local winter site (Cole Green) became unsuitable. Birds using that site presumably went elsewhere or died. The average apparent annual survival rate was 83.5% (or 84.7% if account is taken of the disappearance of Cole Green). In the only other similar study, in northern Germany, the mean return rate was only 56%, with few birds returning in the year after a severe winter. In the Hertfordshire study, there is a correlation between the overall return rate of colour ringed birds from one winter to the next and the number of nights with air frost in the first winter (r = -0.86, n = 7, P < 0.05). These results suggest that birds suffer increased mortality in severe winters.

Territoriality

One of the interesting things that became apparent, once individuals could be identified using colour-rings, was that some of the Hertfordshire Green Sandpiper were highly territorial, with similar patterns of behaviour each year.

blog2 fight 2

When Green Sandpipers appear in late summer they are usually found in small flocks, which include the colour-ringed full-grown adults and young birds of the year. At some point in the autumn, possibly triggered by low temperature or shortening day-length, the behaviour suddenly changes, with some of the birds establishing defended territories on the lagoons, from which they chase all interlopers. This initial burst of territoriality has been captured in the excellent images above and below this paragraph. Once the territories are established they are maintained by subtle calling displays, with only occasional full-on disputes.

blog2 fight 1

During periods of very cold weather, additional birds arrived from other local sites and, for a short period in January 1984, the number of birds present on the reserve more than doubled (to a total of 16). The newly-arrived birds attempted to establish their own territories and devoted up to half of their time to boundary disputes, far in excess of that of the residents. When the weather conditions improved the additional birds left the reserve.

Territorial disputes

During the autumn and early winter of 1985, the research team attempted to investigate territoriality through activity watches of birds present on the lagoon at Lemsford. Every minute, each bird was scored as feeding, resting or disputing. Most watches were over at least one hour and all were completed during the period October to December. On the graph, the solid line and points are the counts of the numbers of birds, and the open symbols are the percentage of time that birds spent in dispute.

blog2 aggression graph

From early October, which corresponds to the end of the autumn moult, between 6 and 11 birds were present at Lemsford, feeding together as a group with little or no interaction. Around mid-October, the number of disputes started to increase. It varied in intensity from day to day but, over a few weeks, the numbers of birds present fell to four or five. These birds took ownership of exclusive territories that were largely maintained for the whole of the winter. Ken Smith was able to find all of the missing Green Sandpipers within 15 km of Lemsford. Some of these individuals would occasionally pop back to Lemsford, get involved in a fight and leave again. In extreme weather interlopers can spend the whole day trying to feed on the lagoons and being chased off.

Tom SpellerFrom observations at Lemsford, it appears that, once territories have been established, local birds are well aware of their boundaries and neighbours. Should a bird stray into a neighbouring bird’s patch, a low-key call is sufficient warning to avoid a disagreement. Ken reports that the big disputes, with chasing and out-and-out aggression, only occur when the territories are being established or when a new bird tries to feed in an established territory. During extremely cold weather, in the 1980s, there would be lots of extra birds attempting to feed in the spring-fed watercress beds, by trying to squeeze into perceived gaps between territories. Such cold conditions are very rare nowadays.

A changing climate

Over the three decades of the project, there has been a tendency for cold winter temperatures to become less frequent across Britain & Ireland. During this time, the distribution of Green Sandpipers has expanded northwards, as you can see in the figure below.

blog2 3 maps

The left-hand and central maps show the winter distributions of Green Sandpiper in the periods of the two winter atlases of 1981-84 and 2007-11, respectively. The surveys underpinning these maps were organised by the British Trust for Ornithology with BirdWatch Ireland and the Scottish Ornithologists’ Club. The expansion of the range represents a 56% increase in occupied 10-km squares, with an obvious extension into Scotland and across northern England, where winter temperatures are colder. Data collected for Bird Atlas 2007-11 included measures of effort, enabling relative abundance to be quantified. In the right-hand map, darker squares represent areas with higher numbers of Green Sandpipers. The Lemsford site is marked with a star.

As, mentioned earlier, there is an indication that annual return rates to Lemsford (and in the German study) relate to the conditions birds experience in the winter period prior to departure for their breeding grounds. In Scotland and Northern England, where freezing conditions occur more frequently, it might be expected that survival rates will be lower than in southern England. For winter populations to establish themselves in new (colder) sites, young birds will need to spend their first winters in these areas and then return in subsequent years. Local population can potentially grow unless or until knocked back by a cold winter.

Where to in spring?

blog2 previous.jpgIn recent years, the research team have deployed harness-mounted geolocators to ascertain the movements of a small number of individuals during the course of a full annual cycle. Another WaderTales blog discusses migration and the effects of harnesses on the behaviour of individuals. See Green Sandpipers & Geolocators.

Summary and papers

This thirty-year study is an excellent example of what can be discovered through long-term observations of a small population of waders. You can read more about the Hertfordshire Green Sandpiper research in these papers (links in bold):

  • K W Smith, J M Reed & B E Trevis (1984) Studies of green sandpipers wintering in southern England. Wader Study Group Bull, 42.
  • K W Smith (1986) Green Sandpiper. In The Atlas of Wintering Birds in Britain and Ireland, pp 222-223, Poyser, Carlton.
  • K W Smith, J M Reed & B E Trevis (1992) Habitat use and site fidelity of green sandpipers Tringa ochropus wintering in southern England. Bird Study, 39, 155-164.
  • Smith, K W, Reed, J M & Trevis, B E (1999) Nocturnal and diurnal activity patterns and roosting sites of Green Sandpipers Tringa ochropus wintering in southern England. Ringing & Migration, 19, 315-322.
  • Smith K W (2002) Green sandpiper in The Migration Atlas: movements of the birds of Britain and Ireland. Wernham C V, Toms M P, Marchant J H, Clark J A, Siriwardena G M & Baillie S R. (eds). T & A D Poyser, London.
  • Smith, K.W., Trevis, B.E. & Reed, M. (2018). The effects of leg-loop harnesses and geolocators on the diurnal activity patterns of Green Sandpipers Tringa ochropus in winter. Ringing & Migration 32: 104-109.

 


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

Green Sandpipers and Geolocators

In a paper in the BTO journal, Ringing & Migration, Ken Smith and his collaborators review how wearing a tag, attached using a harness, affects the preening and feeding behaviour of Green Sandpipers. What did they find and where do their Hertfordshire birds spend the summer?

The lives of Green Sandpipers

Tom SpellerAccording to BirdLife International’s Data Zone page, there are between 1.2 million and 3.6 million Green Sandpipers across Europe and Asia. The breadth of this estimate reflects the difficulty of assessing the population of a species that breeds in wet forest clearings, from western Norway to about 155 degrees east in Russia. It’s hardly any easier to count them in the winter, sprinkled as there are around small pools, in ditches and along river valleys from West Africa to Japan.

The occasional pair of Green Sandpipers breed in the UK and Population Estimates of Birds in Great Britain and the United Kingdom, published in British Birds by Andy Musgrove at al suggests, that fewer than 1000 birds spend the winter here, although rather more are seen on passage between Scandinavia and Africa. In an ever-changing world, studying populations of a species that is at the edge of its range has the potential to explain patterns of loss (or gain) that are less obvious in the heart of a species’ distribution.

Why use geolocators? 

In a previous blog (Bar-tailed Godwits: migration & survival), it was shown that colour-rings, which enable individual recognition of a bird without capture, provided 30 times as much information about annual survival as a metal ring. Adding a geolocator takes you into a new data-rich environment. A geolocator is a small device that records the location of an animal. By recapturing a bird a year after ringing and downloading these data, important information about the timing of migration, the duration of stop-overs at fuelling sites and the exact breeding and/or wintering location can be ascertained.

One of the important things to appreciate about scientists who study bird migration is that they are as keen as any other birdwatcher to ensure that the tracking devices they use cause as little disturbance to the normal life of their study birds as possible.

Attaching geolocators

light geolocator

Geolocator with a light-stalk

In shorebird research, the most common form of geolocator is one that is attached to a ring on the bird’s leg. For most individuals, these devices do not have any negative effects but for smaller waders there can be some problems. Shorebird ecologists from around the globe cooperated to review these issues , publishing it in Movement Ecology. It is summarised in the WaderTales blog, Are there costs to wearing a geolocator? Hopefully, anyone contemplating a new shorebird study will read these before starting. Any data that are collected are only valuable if the birds are either unaffected by the equipment and attachment methods or, if there are effects, these do not prejudice the scientific integrity of the study or the welfare of the birds.

GPS

GPS geolocator, fitted with elastic loops to form the harness

In this study, the Green Sandpipers were fitted with leg loop harnesses, first described by Rappole and Tipton, the authors having decided that ring-mounted geolocators might be too bulky on such a small wader. These harnesses are looped around the top part of a bird’s legs so that the geolocator sits like a small rucsac on the lower back, nestled in the feathers. In the figure below, the left picture shows a tagged bird; you may just make out a slight lifting of the back feathers over the top of the geolocator light stalk. The right-hand picture has been annotated to show how the ‘rucsac’ is fitted.

annotated

The geolocators and harnesses represented 1.4–1.6% of the body mass of the birds. In the study, two different types of device were used, light-level geolocators and GPS geolocators – see the details in the paper. The effects of tagging on behaviour patterns have been examined and written up as a paper in the BTO journal Ringing & Migration, using data collected from seven Green Sandpipers that were fitted with harnesses.

Feeding and preening behaviour

Ken Smith and his colleagues have been studying the Green Sandpipers wintering at Lemsford Springs Nature Reserve in Hertfordshire, southeast England for over thirty years. These shallow lagoons were previously managed as watercress beds. In this particular investigation, the scientists compared the behaviour patterns of individual birds fitted with geolocators, before and after tagging, with a control group of untagged birds. They were particularly interested in the proportion of time spent feeding and preening. Feeding time was thought to be an indication of normal foraging behaviour and preening would be an indication of any discomfort or unfamiliarity caused by the tags and harnesses.

lemsford

Green Sandpipers spend their time feeding, preening and roosting, with most of the feeding activity occurring in loosely defined territories. Four of the tagged birds could be viewed regularly and their activities were observed alongside seven untagged (but colour-ringed) individuals. The amount of time spent feeding increased as days lengthened in the spring and birds prepared for migration. Previous research has shown that the Green Sandpipers on this site are not constrained by feeding opportunities, except in the coldest of condition. In these latter circumstances birds will also feed at night but normally they only feed during the day.

Investigating tag effects

Picture1Lemsford is a well-watched site. Most birdwatchers couldn’t tell which birds were tagged and which ones were not. The tags were so well preened into the plumage that they were extremely difficult to see, even in high-quality photographs. The tags could only be spotted by experienced observers and tag-effects could only be established using 20,000 minutes of observations. A less-intensive study would have showed no significant effects. These bullet points summarise more detailed findings in the paper:

  • All four tagged birds that were closely observed in this study returned successfully from their breeding areas and three of the tags were retrieved. There were no apparent signs of any problems such as skin abrasion or feather wear, caused by the tags or harnesses, and the birds continued to be observed after their tags were removed. The one bird that evaded capture and whose tag was not retrieved was present throughout the second winter.
  • Within the wider group, eight out of ten birds with tags returned the next winter, which is not significantly different from the overall return rate for untagged birds.
  • Tagged birds spent a small but significantly higher percentage of their time preening than untagged birds (untagged birds 4.6%, tagged birds 6.3%). Comparing the periods immediately before and after tagging for the four tagged birds for which detailed observations were collected, there were no differences in the time spent feeding but a significantly higher proportion of the time was spent preening (rather than just resting).
  • Birds may well get used to their tags over time. Of the three tagged birds for which there was sufficient data, two showed significant declines in the proportion of time spent preening over time (15% down to 5%), whereas one was at 6% throughout.

Where do these Green Sandpipers go?

Colour-ringing at Lemsford had already shown that birds are very site-faithful during the winter, once autumn passage birds have moved through. There’s more about this in a previous paper in Bird StudyHabitat use and site fidelity of Green Sandpipers Tringa ochropus wintering in southern England.

BTO map.jpg

This map is available from the BTO website

At the time that the Migration Atlas (Movements of the Birds of Britain & Ireland) was written, using data collected between 1909 and 1997, there was only one record of a BTO-ringed bird in its breeding area. That bird was found in Sweden, and there has been one other in Finland since. Green Sandpipers are not easy birds to observe and, although the long-term colour-ringing project at Lemsford Springs has generated large numbers of local re-sightings, there have been none elsewhere. Early results from the geolocator study show that the Lemsford wintering birds breed in Norway (2), Sweden (3) and Finland (1). A paper will be produced once a larger sample of results is available for analysis; it will look at migration strategies as well as breeding locations.

There is a WaderTales blog that summarises migration of over 40 wader species to, from and through Britain & Ireland: Which wader, when and why?

This paper

Neil Beadle - twoAlthough this study has involved small numbers of tagged and untagged birds, it has shown a consistent pattern of increase in the proportion of time spent preening by birds after tagging, with some evidence that this subsequently decreases over time. There is no evidence of an adverse impact on return rates of tagged birds from one winter to the next, although with such small sample sizes only a major change would have been detectable.

This paper is published in the BTO journal, Ringing & Migration:

The effects of leg-loop harnesses and geolocators on the diurnal activity patterns of Green Sandpipers in winter Ken W. Smith, Barry E. Trevis and Mike Reed


 GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton