Chester Clinic

 

Bb feb 2010 -

The population biology
of Common Sandpipers
in Britain
T. W. Dougall, P. K. Holland and D. W. Yalden Abstract The population biology of Common Sandpipers Actitis hypoleucos has
been studied, especially by colour-ringing breeding adults, at two sites, in the Peak
District and in the Scottish Borders. Adults are usually site-faithful, males more so
than females, contributing to a good apparent survival rate (72% and 67%,
respectively). Some, at least, return to breed at one year old, but usually not to the
site where they hatched. The population in Britain seems to be in slow decline,
most obviously indicated by a contraction along the edges of its range, which
results especially from poor recruitment of young birds. This does not seem to be
due to poorer breeding success, but it is uncertain whether it is caused by a subtle
effect of climate change, change in quality of stopover sites on migration, or
changes in wintering habitat. Since we don't know precisely where British birds
spend the winter, the last possibility is especially hard to evaluate.
or Wood Lark Lullula arborea, but not suffi- The Common Sandpiper Actitis hypoleucos is ciently abundant to benefit from mass one of those ‘in between' birds – not rare studies, like the Blue Tit Cyanistes caeruleus enough to have attracted devoted individual or Robin Erithacus rubecula. Unlike many attention, like the Osprey Pandion haliaetus waders, it does not flock in large numbers to British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
fields, estuaries or the Bancd'Arguin, it is not censused bymoorland bird counts, andwhen on migration does not get ringed in any great numbers. There is a littleinformation from the Water- ways Bird Survey on popula- tion trends and the species seems to have been targeted by only one PhD study (Mee 2001). Our own, essentiallyspare-time, efforts have beenan attempt to fill in some of the gaps. In reviewing whatwe have learnt, we inevitably also highlight how much remains unknown.
Study sites and
Fig. 1. Sketch map of the Ashop–Alport study site and the nearby
reservoirs in the Upper Derwent Valley, Peak District (areas of Our efforts started with a woodland shown in green, water features in blue; also shown is the survey of numbers in the Peak A57 between Manchester and Sheffield) (from Dougall et al. 2005).
District in 1977–79, combinedwith a colour-ringing study ofbirds along a 10-km stretch of the Rivers Ashop (‘Snake Pass') and Alport (Holland etal. 1982a,b). Of about 200pairs then breeding in the Peak District, 20–22 pairs occupied these valleys, withanother 45–50 pairs nearby on the Ladybower-Derwent- Howden (LDH) Reservoirchain. The Ashop flows intothe western arm of LadybowerReservoir, about 2 km down- stream of the study site; thewhole forms part of theUpper Derwent catchment.
The colour-ringing study con- tinues to the present day,giving 32 years of data (PKH, then DWY), but has also beenextended to the reservoirchain. Thinking that a com-parative study would be revealing, we started a parallel investigation on the riversLeithen Water (8.5 km) and Fig. 2. Sketch map of the Borders study site (woodland in green,
Heriot Water (6 km) in the water features in blue; also shown is the B709 road fromEdinburgh to Innerleithen) (from Dougall et al. 2005).
Moorfoot Hills, Borders, in British Birds 103 • February 2010 • 100–114 Dougall et al.
1993 (TWD), and this also continues returning migrants than the Peak District (Dougall et al. 2005; Pearce-Higgins et al. (hereafter referred to as Ashop) study area.
2009). This study site, and our knowledge of On the other hand, the LDH reservoir chain the species, benefited from an intensive PhD has a shoreline of 30 km. This must also study in 1998–99 (Mee 2001). The two provide a good target for returning sand- stretches of river are about 6 km apart, and pipers, but is too extensive to be studied as together perhaps provide a larger target for intensively as the rivers. The whole shoreline has been surveyedtwice (once in May,once in June) eachyear since 1992, andone or two ex-Ashopbirds are invariablypresent.
Adults are usually caught on the riversin short, single-panelmist-nets set withinthe usually targetingparticular individ-uals, and birds areringed with 3–4Darvic colour rings,as well as a BTO metal ring, so that individuals are sub- 29. An upper stretch of Glentress Water, near Blackhopebyres, in the
sequently recognis- Borders study area. This shows the meandering river and the wide shingle able in the field. In banks that develop in the bends, producing favoured feeding sites for Common Sandpipers Actitis hypoleucos. area, potential terri-tories are checkedweekly through Mayand June, sometimesinto mid July, for thepresence of colour-ringed birds. Nestsare rarely located,and the adults aresecretive incubation, but oncethe chicks hatch,their parents becomevery vocal (‘alarm'),revealing roughlywhere their chicksare. By backing off,or using a car as a hide, it is sometimes possible to watch 30. A lower stretch of the Borders study site, on Glentress Water near
adults returning to Whitehope. This is good habitat for Common Sandpipers Actitis hypoleucos, brood young chicks.
with wide shingle beds, cover for chicks in the boulders, and with theadvantage of the nearby road, allowing a car to be used as a hide; May 2009.
Every effort is made British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
to ring these, with a single(‘scheme') colour ring anda BTO metal ring. Ashopbirds receive a white ringon the right tibia as thescheme mark, while thosearound the reservoirs get alight blue ring on the lefttibia. The hope was thatrecruits to the Ashop fromthe reservoirs would bequickly recognised. In theBorders, chicks as well asadults were formerly fittedwith individually recognis- able combinations, but in more recent years both 31. ‘Walk-in' traps set at the waterline of Ladybower Reservoir,
chicks and adults have May 2009. Two traps are set, facing in opposite directions, and with scheme colours applied to boulders or other debris to mask the outline of the trap, and the right leg only: red on mealworms on the bait trays as an added attraction.
tibia, orange over BTO on tarsus for adults; quickly (and noisily) pair up, usually in their orange on tibia, red over BTO on tarsus for old territories, and have eggs by mid May. It chicks. So far, neither Peak District nor Moor- seems as though they fly into their territories foot Hills birds have been seen in the recip- very quickly (rather than trickle slowly up rocal study area, but a juvenile ringed on through the country, although there are some autumn passage in Lancashire on 4th August sightings in south and southwest England, 2001 (by PKH) was retrapped as a breeding and in Wales, of colour-ringed Borders bird south of Peebles, just outside the Moor- birds). This impression is heightened by the foots study area, on 29th May 2003. The age fact that they get back to their territories in of the chicks (and hence their hatch date) can the Borders about a week earlier than those be estimated from their bill length, and in the Peak District. Young birds arrive back weight relative to age gives an estimate of 5–10 days later, on average, than the old condition (Holland & Yalden 1991b). Sexing hands. Territories are usually 150–200 m long Common Sandpipers is not easy, though when there are neighbours to constrain females are generally slightly larger (means them, and are generally along stretches of 54 g v. 49 g; Mee 2001). The greater weights of shingle shore with some cover for the chicks females during egg-laying are revealing (they (e.g. undercut shores, boulders, taller vegeta- can weigh up to 82 g), and with colour-ringed tion). Females typically lay a clutch of four birds courtship behaviour can be helpful in eggs (mean 3.65) in a nest on a grassy bank a determining the sex of individuals. However, few metres back from the water, but some- both adults incubate, brood chicks and times on shingle islands or at the top of stony defend their territory against neighbours reservoir shores; occasionally the nest may be (sometimes making the mistake of chal- over 100 m from the waterside. Incubation is lenging their own returning mates!).
shared, but males sit mainly overnight and Although the male usually follows behind the females during daylight hours (Mee 2001). female while she is feeding up prior to egg- The eggs hatch from mid May (Borders) laying, and signals to her with ‘wings-up', dis- or the last few days of May into early June, playing the strongly patterned underwing, the but new recruits are later and pairs will same display is used as a threat by both sexes. produce a replacement clutch if the first islost, stretching the hatch dates to as late as 7th July. At hatching, chicks weigh around Older Common Sandpipers reappear on 9.5 g and have a bill length of about 10 mm.
their breeding grounds in mid to late April, Chicks are encouraged from the nest by their British Birds 103 • February 2010 • 100–114 Dougall et al.
.Yalden. W 32. A typical Common Sandpiper Actitis
hypoleucos nest, with a clutch of four eggs; this 33. A late, replacement nest, in growing
one, in a patch of Bracken Pteridium aquilinum in Bracken Pteridium aquilinum, Ashop Valley, the Ashop study area, 15th May 1984, belonged 9th June 1982; another of Red-Red's successful to the long-lived male ‘Red-Red'.
parents, and for their first few days usually this age to fledging: their camouflage, ability frequent damp areas – rushes, streams trick- to run and hide, and to dive and swim if sur- ling over reservoir shores – where small prised near deeper water, gives them an insects are readily available. Mortality at this ability to dodge most predators (and stage is high, around 25% (Yalden & Dougall ringers!). Detailed observations suggest that 2004), despite both parents being present as they are thermally independent by then, guards. Young chicks need brooding every though older chicks may still be brooded in seven minutes or so, and for about seven rain and at night. From about seven days old, minutes each bout. By seven days, the chicks the chicks may be closely attended by only are mobile, weigh around 16 g and have a bill one parent, the other going off to feed nearby length of 14 mm; most (75%) survive from (though still alert to intruders). By their third week (the chicks usuallyfledge in 19 days), oftenonly one parent is leftguarding the chicks, andusually stays beyondfledging for another weekor so. When one parentleaves early, it is usually,but not always, the female.
Partial desertion is morelikely with later-hatchingbroods (Mee 2001).
Clearly, their territory is ver y important toCommon Sandpipers;both adults defend itagainst their neighbours.
Moreover, it is demon- strably the stretch of shoreline that they are 34. A brood of three young Common Sandpiper Actitis hypoleucos
defending: the four neigh- chicks, about four days old and about 20 m away from their knownnest-site; June 2009, Ladybower Reservoir. bours will feed together British Birds 103 • February 2010 • 100–114

Common Sandpipers in Britain
comfortably in nearbypasture, but renew ter-ritorial aggressionwhen they return tothe river. An analysisof habitat suggeststhat they need an areaof shingle, and theadults spend muchtime patrolling thewater's edge in searchof food. However,their diet contains aneven mix of aquaticprey (caddisfly (Tri-choptera), (Ephemer optera) andstonefly (Plecoptera)larvae) and terrestrial prey (click beetles 35. A young Common Sandpiper Actitis hypoleucos chick, probably only a
(Elateridae), carabids day or two old, still with a short (10 mm) bill; Whiteholme Reservoir,Yorkshire, June 2008.
earth worms (Lumbricidae)) (Yalden 1986), and low recruitment. The Ashop had 20–22 so reliance on the water's edge to provide a pairs in 1977–80. However, the severe late food supply is not the whole story. The most April (24th–26th) snowfall of 1981 apparently prolonged territorial fight we have observed surprised, and killed, a number of returning (27 minutes) involved two pairs guarding adults; the population dropped to 14 pairs chicks, on 18th June 1989. One pair, dis- that year, and recovered only slowly (by one turbed by an angler, led its chicks into the or two pairs a year) up to 1988 (Holland & neighbouring territory, and to start with all Yalden 1995). Another cold, late spring in four birds were fighting (three of them were 1989 then caused another sharp decline, from colour-ringed) (Yalden 1992a). One male which the population has never properly then led his chicks back, while his mate con- recovered. Although there were 15 pairs in tinued fighting for another 11 minutes. Such 2006, only five pairs were present in 2007 and observations suggest that the most important 2008. Averaged over 28 years, the population roles of the territory are toprovide the chicks with a feeding area and good cover.
Territorial fights are certainlymore prolonged when chicks are also present than early inthe season, when the briefest of challenges is usually sufficient to maintain territorial integrity.
The early years of study in thePeak District, and the early years of the Waterways Bird Survey (WBS), suggested a Fig. 3. The long-term decline of the Ashop–Alport Common
stable population, as might be Sandpiper Actitis hypoleucos population from 1977 to 2009, and expected for a relatively long- the fluctuating population in the Borders study site from 1993 lived species with high survival British Birds 103 • February 2010 • 100–114 Dougall et al.
has declined by 59%. This matches what has Survival rates, breeding success
happened more generally on the streams around the Peak District, and the national We have tried hard to understand the basis of trend revealed by WBS and BBS (Breeding the national decline, and the contrast in for- Bird Survey), which suggests a 25% decline tunes between the Peak District and Borders over eight years (www.bto.org/birdtrends/ populations. Originally (1970s and 1980s) wcrcomsa.htm). Over the shorter run of data there was a strong correlation between sur- from the Borders, there seems to have been vival rates and minimum temperatures in no decline, though much variability. Even late April: fewer adults returned in cold more puzzling, the LDH reservoir population springs. Simple apparent survival rates near the Ashop also shows no such decline.
(resighting of the previous year's colour- There were 49 (±8) pairs in the early 1980s ringed adults, on average 72% for males and and 51 (±11) pairs in the 1990s and 2000s; 67% for females) declined between 80% and indeed the highest count ever was as recent as 47% as late April mean minimum tempera- 2007, when 84 pairs were logged. In the ture went down from 5.6 to 1°C (Holland & Moorfoots, along a discontinuous 10.13 km, Yalden 2002a). The variation in population monitored annually between 1993 and 2007, this produced matched changes in the North the number of territories ranged between 14 Atlantic Oscillation (NAO); warm wet in 2000 and 31 in 1993, and the percentage winters (high NAO, perhaps snowier) are bad which hatched at least one chick ranged for sandpipers (Forchammer et al. 1998).
between 48% (in 2004) and 82% (in 2003) However, in the 1990s, this relationship no (Dougall et al. 1999; Dougall unpubl.). longer fitted, though survival rates were still While estimating the national population just as variable, as were April temperatures is fraught with difficulties (see below), it is (Dougall et al. 2004). Not only did the easier to map the breeding distribution.
Borders population not show the long-term Between the two breeding atlases (1968–72 decline, but the considerable variations in (Sharrock 1976) and 1988–91 (Gibbons et al.
populations there from year to year were not 1993)), the breeding range contracted, partic- correlated with those in the Ashop popula- ularly along the fringes of the species' range.
tion (Pearce-Higgins et al. 2009). If anything, An apparent net loss of 14% of its breeding survival rates were slightly higher in the range in Great Britain and a substantial, declining Ashop population than in the though perhaps overestimated, 54% of its Borders population, although the difference Irish range suggests a considerable decline was not significant. (Yalden 1993). It will be fascinating to see Breeding success is hard to evaluate pre- what the third atlas reveals.
cisely; because well-grown chicks are so good at running and hiding from any threat, whether ringer or pred-ator, counts of older young or fledglings are invariably underes- timates. One calculation suggeststhat perhaps 35% of the actual fledglings were not recorded(Yalden & Dougall 2004), another that 30% were missed (Holland & Yalden 1994). However, the fact that their guarding parents are so vocal suggests that at least the Fig. 4. This figure shows the slight negative correlation of
success of breeding attempts can annual adult survival for the Ashop birds with winter North be reliably counted: a territory Atlantic Oscillation (NAO) values (yellow circles denote first- that has ‘alarming' parents over year birds, i.e. new recruits, red circles represent older three or four weeks has surely got adults) (from Pearce-Higgins et al. 2009). A higher NAO valueindicates a warmer, wetter winter in western Europe, but at least one chick through to cooler, drier conditions in NW Africa.
fledging. On that basis, there is no British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
evidence that breeding success has been mate at least once (Holland & Yalden 1994).
poorer in the Ashop study area than in the The converse pleasure is of discovering Borders study area over the decade or more that individual birds which have failed to that both have been studied. What is clear, return to their territories have moved else- however, is that recruitment of ‘new' birds, as where (emigrated) rather than died. Obvi- well as returns of fledglings, is very much ously, this does not happen often. One 1980 higher in the Borders than in the Peak Dis- female that had been presumed dead in the trict. Only one of the 99 chicks and fledglings 1981 spring was found in 1982, about 20 km ringed in the Ashop study area over the 1990s away to the southwest in the Goyt Valley, returned to breed there, but 49 of 421 ringed where she returned in 1983 and 1984. In in the Borders did so. Over the same period, 1990–93, ten birds from the supposedly site- while 68 adults were recruited to the Ashop faithful Ashop population contributed population, there were 172 new adults ringed further to the decline there by moving to in the Borders (Dougall et al. 2005). The LDH. One, having bred successfully along the attempt to identify the source of new recruits Ashop in 1992, as a new recruit, returned to the Ashop population did find four birds there briefly in April 1993, but in June 1993 bearing LDH light blue rings, including what was at Derwent Reservoir, guarding a family, has become the record for longevity. A 13- as he was in 1994, 1995, 1996 and 1997. This day-old chick ringed as NV54164 at Lady- example highlights one of the mysteries of bower Reservoir on 21st June 1992 turned up this species. What are returning birds, as a breeding male 7 km away in one of the whether old hands or new recruits, looking upper territories on the Ashop in May 1993, for when they get back? If they were heading with an unringed female. Both were caught for familiar habitat, we might expect riverine and individually colour-ringed, but their birds to return to rivers and reservoir birds to breeding attempt failed that year, and the return to similar shorelines. Obviously, estab- female was never seen again. The male didn't lished birds return to their familiar territory, return to the Ashop, but in May 1994 was and get back to claim it as quickly as possible.
seen three times with an unringed female at Often, they also meet their old mate there, Ladybower, about 3 km south of where he and experienced birds are more likely to hatched. He was seen back in that territory breed successfully together (Mee 2001).
every year to 2007, being last recorded on Rarely, females get back before their mate, 19th June 2007; moreover, judging by his and may then pair with an already estab- ‘alarming' behaviour in June, he bred suc- lished (but different) male. Are birds that cessfully in 11 of his 14 years at Ladybower, move sites ones whose mate fails to return? and at 15 years old was much the oldest Are they looking to set up territories near Common Sandpiper that we or anyone else other, already established, birds or pairs, on has recorded.
the basis that their presence signifies a suit- This sort of resighting is one of the able site? If the latter is true, it might explain delights of studying this species. The birds the geographical retreat from peripheral are highly site-faithful (and if they were not, parts of the range, in the Peak District cer- the apparent survival rates would be much tainly, but also in northeast Scotland and in poorer). An early calculation was that 89% of Ireland, as revealed by Gibbons et al. (1993).
returning males and 78% of returning It is possible that some of the apparent con- females came back to the same or an adjacent traction in range was actually a consequence territory (Holland & Yalden 2002a). So, in of less thorough surveying of the thinly pop- late April, checking the rivers to see who is ulated periphery of the species' range in safely back, and with whom they are paired, 1988–91, especially in Ireland, although local is a special pleasure. With an average survival accounts confirm losses in many areas.
rate of about 80%, adult life is likely to lastthree years, so the chances of both members of a pair returning are only about 50%. Put Given that chicks wear at least a scheme ring, another way, a bird that holds territory for any that return to our study areas are con- three years is statistically ‘bound' to get a new spicuous, and targeted (albeit not always suc- British Birds 103 • February 2010 • 100–114 Dougall et al.
perhaps a large proportion, ofthem. This is an aspect of ourstudies where sightings fromothers would be especially valu-able.
Migration and wintering
This section deals with our biggest
uncertainties! There are ringing
recoveries of British birds moving
south in Britain, and from France,
Spain, Portugal and Morocco, in
July–October. Similarly, there are
recoveries of returning birds,
through Morocco, Spain and
France in March–April. These include recoveries/resightings of 36. A well-grown Common Sandpiper Actitis hypoleucos chick,
our own birds in southern within about two days of fledging (bill length 19.7 mm, wing England, France, Iberia and length 79 mm, but underweight at 27.5 g), showing remnants Morocco. None of our birds has of chick down on the nape and tail. The red ring above the been seen in November–February, BTO metal ring identifies this as a chick from the Borders and, more surprisingly, there has study site; Leithen Water, June 2005.
been just one recovery from West cessfully) for recapture, identification and Africa of the 19,000+ Common Sandpipers full colour-ringing. This gives us a measure ringed in Britain. This was of a bird ringed at of natal dispersal – the distance between Abberton Reservoir, Essex, in July 1964 and hatching and establishment of a breeding ter- recovered in Guinea-Bissau in September ritory in later years – but this is clearly going (though birds ringed at Abberton are mostly to be an underestimate, since we are more Scandinavian birds on passage, as nine other likely to detect a ringed new recruit within recoveries in Scandinavia testify). The nearest our study areas than farther afield. Of 36 thing to a recover y in West Africa of a Borders chicks that returned later to breed, British-bred bird involves an unfortunate they were between 0 and 39 km from where chick ringed at Grassington, Yorkshire, on they hatched, and at a median distance of 6 2nd June 1963. Its remains were recovered on km. It is probably no coincidence that this is 20th November 1963 from the radiator of an roughly the distance between the two parts, aircraft that landed at Moscow airport after a Heriot Water and Leithen Water, of the study journey from Accra (Ghana) via Conakry site. In the Peak District, the 35 returning (Guinea), Bamako (Mali) and Belgrade. The chicks were between 0.7 and 138 km away, likelihood is that this young bird had been with a median of 3.3 km, which is, similarly, caught up in Guinea or Mali; this is roughly roughly the distance between the Ashop and where we would predict British birds to be in the LDH reservoirs (Dougall et al. 2005).
winter on the basis of the SSW trend shown How biased are these two figures? We have by recoveries of Common Sandpipers ringed had a few exchanges between the Goyt Valley, elsewhere in Europe (Poland, Germany, 20 km to the southwest, and the Upper Russia) and recovered in West Africa Derwent, and there is a weak correlation, (Holland & Yalden 2002b).
with a two-year lag, between population Common Sandpipers move south in changes in the Ashop population and those summer very quickly. Our study sites are in the Goyt. The most distant return, at 138 usually already thinly populated by early July, km, was in north Wales. If our returns are and typically empty before the end of the spread so far, it is obvious that a search con- month. Some have been recovered in Por- centrated within 10 km or so of the sites of tugal and Spain as early as mid July, and we ringing is going to miss a proportion, suspect that failed breeders may leave for British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
Africa very quickly. One Peak District bird at St Abbs Head, Borders (Dougall & Yalden was recovered, already back in Morocco, on 2007). These August falls are presumably of 15th June 1979. On the other hand, we also Scandinavian birds on passage, but the July have recoveries (and sightings of colour- flocks are likely to be from more local ringed birds) into August of sandpipers still breeding areas.
in Britain, and we suspect that juveniles are A small minority of Common Sandpipers in less of a hurry to reach Africa.
remain in Britain overwinter. We know little Over a period of 12 years, PKH succeeded about these, either. On the basis that, in birds in fitting colour rings to 60 full-grown birds generally, those summering farthest north near the mouth of the River Lune. It was winter farthest south, whereas those in the thought that these might be a sample of the middle of the range move relatively little, we 100 pairs or their offspring that breed higher would expect that Scandinavian birds overfly up the Lune catchment. Yet none of these was Britain. Birds wintering in Britain are more ever seen on territory there in later years, nor likely to be part of our summering popula- were any of 38 birds ringed on those tion. The chances of spotting one of our breeding areas ever seen at the mouth.
colour-ringed breeding birds still in Britain However, one was seen later breeding in the in winter seem slight, but would be a worth- Borders (see above) and another in while target for those with telescopes or Northumberland. Evidently, the mouth of digiscoping equipment. If some of the the Lune is a feeding-up site for birds from Common Sandpipers overwintering in the Borders. The mean weight of these birds Britain could be caught and colour-ringed, was 66 g, but the six heaviest weighed 80, 80, they are perhaps more likely to yield a 81, 81, 82 and 84 g. Others have also reported resighting in summer. Birds regularly birds fattening up to over 80 g at sites away hunting along reservoir shores can some- from their breeding grounds (e.g. Brown times be caught in walk-in traps or small spring-traps (Dougall & Yalden 2008). Trap- Relatively large concentrations of ping may also confirm that wintering birds migrating birds sometimes occur in autumn, are site-faithful to their wintering territories, for example 100 at Carron Valley Reservoir, as suggested by one caught on Southampton Upper Forth, on 7th July 1984; 64 at Endrick Water on 6th January 1974 that was caught Mouth, Clyde, on 25th July 1977 and 14th there again on 18th March 1975. The ringing August 1978; and 83 roosting at the River expeditions to Djoudj, Senegal, in the early Dumfries & Gal-loway, on 25th July2003. Occasionallythere are ‘falls' inthe Northern Islesand along the eastcoast of Scotland,most during 18th–22ndAugust 2001, whenthere were 15 onFair Isle; seven onNorth Ronaldsay;50 on the Isle ofMay; 23, 11, nine and eight at foursites in the East Fife; 37. An adult (female?) Common Sandpiper Actitis hypoleucos executing a
seven at Skateraw, ‘double wing-up', showing the striking underwing pattern. This is both a Lothian; and eight threat and a courtship display. Whiteholme Reservoir, Yorkshire, April 2007.
British Birds 103 • February 2010 • 100–114 Dougall et al.
1990s showed that Common Sandpipers (51%) were recorded (Dougall et al. 2005).
ringed there had a higher return rate (9/65 or However, given the median natal dispersal 14% after one year) than any of the other distance of 6 km, and a range up to 39 km, it waders, implying that they were indeed site- is not known if the ‘missing' 49% were in fact faithful (Sauvage et al. 1998). Limited obser- recruited elsewhere, or if mortality rates are vations suggested that they established higher than we assumed. Moreover, we must territories of about 200 m in length along the expect that first-year survival rates vary banks of the Senegal River, and defended widely, as they do for adults, with weather them against neighbours, but there is scope and other conditions, but we know nothing for considerable work on the species' winter of this. Colour-ringing studies of wintering birds, comparing adult and first-year survival We have estimated that around 54% of rates, would be interesting. Although they newly hatched chicks survive to fledging reach adult size by the time they fledge, (Yalden & Dougall 2004), and we have a good juvenile sandpipers have more conspicuous set of estimates for adult survival (more barring on their primary coverts, so they strictly, adult return rates) from resighting would still be recognisable as young birds our colour-ringed birds (see above). Because when they reach Africa.
fledglings rarely return to their natal sites, at Returning birds, as we remarked above, least in the Peak District, we have no clear seem to return quickly to their territories.
estimate of the survival rate of first-year birds However, this is clearly a stressful time. In over their first winter. When the Ashop pop- addition to the suspected, and recorded, ulation was stable, we could create a balanced mortality in 1981, recoveries in other years life table by assuming that 57% of young are quite frequent in late April/early May. A birds survived their first winter. Using that conspicuous example is NV82841, ringed as a assumed survival rate, we might have chick on 8th June 1996 at Garvald Lodge, expected 96 recruits to the Borders popula- Heriot Water. He was not seen again until tion from the 1993–2002 cohorts; and 49 2002, when he was breeding successfully, at David Hutton 38 & 39. Two splendid portraits of Common Sandpiper Actitis hypoleucos ‘Light blue//BTO,
orange/black, photographed on migration at Seaswood Pool, Nuneaton, Warwickshire, on 15th April
2008. It had been ringed as a newly fledged juvenile at Ladybower Reservoir on 10th July 2002.
It was seen in its territory at the northeastern end of Derwent Reservoir in June 2004, June 2005,
May 2007 and June 2008, and was retrapped there on 28th May 2009.
British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
Whitehope, 6 km to the south, and he was rivers. A major problem, of course, is to there again in 2003 and bred successfully translate observed linear densities (per km of with the same mate. On 22nd April 2004, river or shoreline) into sensible figures for though, he was found dead at Devizes, Wilt- areas. Among a variety of estimates, we sug- shire. His mate returned safely, took a new gested that 1.6 pairs per monad (1-km mate, was unsuccessful in breeding and was square) was the most plausible (Dougall et never seen again.
al. 2004), while the BBS suggested that 2% ofthe monads in England and Wales but 15% Estimating the size of the British
of those in Scotland were occupied; there are few data for Ireland, but we assumed that Given our interest in the densities of birds in 5% of monads were occupied. The total our study areas, it was a natural progression occupancy for Britain & Ireland is then to attempt to estimate the size of the total 19,500 monads, with a breeding population breeding population of Britain & Ireland. of 30,622 pairs, twice the number estimated In the New Atlas (Gibbons et al. 1993), it was in Gibbons et al. (1993). Moreover, a recal- suggested that the population of a hectad culation of the appropriate figure for the (10-km square) might be 15 pairs, implying 1968–72 breeding atlas (Sharrock 1976) sug- a population of 15,000 pairs in Great Britain gests a population then of 39,600, and thus a and 2,500 pairs in Ireland. This figure was in decline of 23% between the two breeding part suggested by our earlier estimate of the atlases. A decline of 23% is also suggested by Peak District population (11 pairs per hectad the WBS, albeit between 1989 and 1999 averaged over 18 hectads), tempered by (Dougall et al. 2004). Using the same some acknowledgment of the fact that the methodology, we estimated the nationally species was clearly most abundant in Scot- important Scottish population to be in the land. Since the 1980s, many more surveys range of 17,000–24,000 pairs, most probably have been published, including both local around 19,000 pairs (Dougall & Yalden tetrad atlases and particular surveys of David Hutton British Birds 103 • February 2010 • 100–114 Dougall et al.
Causes of the decline
tering birds) and near our two study sites in Our attempts to explain the decline of the Britain, produced evidence of some effect of national and Ashop populations by studying climatic variation (NAO) on adult survival the population dynamics of the Ashop birds rates, and declining adult survival rates and contrasting these with patterns in the explained the overall population decline; Borders have not been especially fruitful.
however, there was no evidence that any Adult survival rates and breeding success long-term trend in climate was responsible seem comparable between the two areas for the decline of the Ashop population (Dougall et al. 2005). There is clearly a major (Pearce-Higgins et al. 2009). Increased agri- discrepancy in recruitment rates between the cultural use of the wintering grounds or the two areas, but we are not clear what underlies stopover sites on migration might be this. Possibilities include the poorer survival affecting return rates. In Britain, it is evident of first-winter birds in West Africa and that the decline is most marked on smaller poorer survival on migration. If there is streams and rivers. Moreover, this retreat poorer survival of young birds, is this a con- from small streams has been proceeding for a sequence of climatic changes? Alternatively, century or more (Holloway 1996). Are these are new recruits put off by finding poorer sites more affected by agricultural change breeding habitat on the rivers when they get than larger sites? The species is certainly sus- back so that, perhaps, they take territories on ceptible to recreational disturbance, from reservoirs instead? These ideas merit some both anglers and picnickers (Yalden 1992a), and this is regularly cited as a harmful factor.
A recent attempt to correlate changes in The pair described earlier that led their population size from year to year with chicks into their neighbours' territor y, climatic variation, both in Africa (for win- inducing a prolonged fight, did so because an angler was standing in the middleof their own territory. Conversely,the species responds quickly to theprovision of secure sites (islands,fenced areas). However, in the PeakDistrict, reservoir shores suffermore human intrusion than thestreams, so the cause-effect correla-tion is weak.
One interesting possibility is that climate change might beaffecting the populations of somefreshwater prey. Many of thecommon stream larvae prefercolder water (Durance & Ormerod2007). Stream temperatures wouldbe much more sensitive to fluctu-ating weather than reservoirwaters, which are buffered by theirlarge volume. Stream invertebratesare also more exposed to changesin management regimes on neigh-bouring farmland. A regular hazard of mist-netting at dusk usedto be getting dor-beetles Geotrupescaught in the nets; it was quite usual to get three or four in an 40. An adult Common Sandpiper Actitis hypoleucos carrying
just a BTO metal ring – against the grey legs, these are easily
evening whereas now there are not missed; Whiteholme Reservoir, Yorkshire, June 2008.
that many in a season. Are the cow- British Birds 103 • February 2010 • 100–114 Common Sandpipers in Britain
pats now inhospitable to beetle larvae sandpipers do migrate in long hops, it might because of the use of ivermectin vermifuges explain why relatively few are seen in July in on cattle? Many smaller invertebrates also southern England as they migrate south emerge from dung, and are eaten by sand- (although more are seen in August, these are pipers. Reduced sheep numbers mean that probably Scandinavian birds). There are vegetation is now longer along some stretches major uncertainties with this scenario. Some of Heriot Water; chicks are harder to locate, evidence from elsewhere in Europe suggests but they might also be less able to feed freely.
that Common Sandpipers accumulate little In places, the shingle is becoming overgrown, or no weight at stopovers (e.g. Meissner so that too is less suitable feeding habitat.
1997, Arcas 2001). Is this a strategy that An entirely different scenario is suggested varies among populations, or age groups? for the wintering habitat by recent surveywork in West Africa. In some places at least, wintering Common Sandpipers frequent We have learnt much about our favourite mangrove swamps and roost communally, bird in over 30 years of study. What began as though it is not certain whether they also a very local concern (how many Common defend territories while feeding. Trolliet & Sandpipers are there in the Peak District and Fouquet (2004) suggested that 15,000 feed in how is the population balanced?) has mangrove areas and another 8,000 on the expanded to a second study (do Borders mudflats of Guinea; this could be a substan- birds vary the same way?), and to national tial proportion of the British population, if concerns (how many breed, how is the popu- Guinea is where they winter. Mangroves are lation changing?). Now we are faced with highly productive, but also subject to intense problems on a flyway scale. We suspect that it pressure from coastal development, for fish is this wider population that is declining, not farming, timber, and agriculture. Apparently, just the Ashop or British ones (Sanderson et Common Sandpipers exploit the abundance al. (2006) suggested a 49% decline across the of fiddler crabs Uca in this habitat. Therefore, Western Palearctic). Greater understanding this habitat is highly susceptible to human of the species will require a co-ordinated intervention and could be that in which most international effort. We urgently need to of our birds overwinter. However, it is locate the wintering areas and habitats of the unlikely to be affected by winter rainfall or bulk of our birds. If there are routine temperature, as would be expected if the stopover points during migration, these too Sahel region (as at Djoudj) is their main win- need to be established. The attachment of tering area. Thus our failure to detect any satellite or radio tags would be one, albeit obvious relationship between year-on-year expensive, way to do this (cf. the studies of population change and weather variation in White-rumped Sandpiper Calidris fuscicollis; West Africa (Pearce-Higgins et al. 2009) Harrington 1999). An alternative would might fit with such a wintering habitat.
involve routine studies on the wintering Migration remains an area of major areas, similar to ours on the breeding sites.
uncertainty and concern. Fat-free mass seems Given the numbers of ringers and other to be about 40 g (Baccetti et al. 1992). If our ornithologists visiting exotic locations, as birds regularly accumulate 40 g of fat (as well as dedicated expeditions and collabora- implied by birds weighing over 80 g in July), tive studies with local birdwatchers in West and have an average wingspan of 350 mm, we Africa, we hope that someone will take up can calculate that they should have a flight this challenge.
range of 6,000 km in still air (Pennycuick1989). This would easily take them to the Senegal River mouth in one hop, farther if We must thank the estates and farms on whose land they exploit tailwinds. If this is optimistic, we have worked for their permission to do so, and two major refuelling stops in, say, Morocco those who have helped with our fieldwork (as detailed and Senegal would enable an easier migra- in, for example, Dougall et al. 2005). We also thank thephotographers for the accompanying images. Sightings tion; if such sites exist, they need to be identi- of colour-ringed birds away from our study sites can fied so that they can be protected. If be reported to [email protected] British Birds 103 • February 2010 • 100–114 Dougall et al.
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