Contrasting trends in two Black-tailed Godwit populations: a review of causes and recommendations

Abstract

In recent decades, the West European population of Black-tailed Godwits, Limosa limosa limosa, has declined in size at a quite alarming rate, while the Icelandic population, L. l. islandica, has undergone a rapid increase in population size. These two populations have been the subject of a great deal of research, much of which has been focused on understanding the causes and consequences of the contrasting population trends. In 2007, a workshop was held during the annual conference of the International Wader Study Group at La Rochelle, France, with the aims of identifying the likely causes of the population changes and providing recommendations for future actions to improve the conservation of both populations. The available evidence strongly suggests that changes in productivity as a consequence of agricultural intensification are the most likely driver of the decline in L. l. limosa, although the concentration of much of the population in just a few sites in winter and spring is likely to exacerbate their vulnerability to future habitat changes. Agricultural and climatic changes are implicated in the expansion of L. l. islandica, and the availability of both intertidal mudflats and wet grasslands as foraging habitats appears to be very important across much of the winter range of this population. A series of recommendations for actions to conserve both populations are provided, including improving agricultural land management and protecting key passage and winter sites and habitats.

Full text

Bulletin 114 December 2007
43
Gill et al.: Contrasting population trends of Black-tailed Godwit subspecies limosa and islandica
43
The last three decades have seen widespread declines in
the population size of many species of shorebird (Interna-
tional Wader Study Group 2003). While research has strongly
implicated the loss and degradation of breeding habitats in
these declines, largely through drainage of wetlands and
conversion to intensive agriculture (Thorup 2006), efforts to
reverse declining population trends have met with little suc-
cess. The West European population of Black-tailed Godwits,
Contrasting trends in two Black-tailed Godwit populations:
a review of causes and recommendations
JENNIFER A. GILL1, ROWENA H.W. LANGSTON2, JOSÉ A. ALVES1, PHILIP W. ATKINSON3,
PIERRICK BOCHER4, NUNO CIDRAES VIEIRA5, NICOLA J. CROCKFORD2, GUILLAUME GÉLINAUD6,
NIKO GROEN7, TÓMAS G. GUNNARSSON1,8, BECCA HAYHOW1, JOS HOOIJMEIJER7,
ROSEMARIE KENTIE7, DAVID KLEIJN9, PEDRO M. LOURENÇO7, JOSÉ A. MASERO10,
FRANCIS MEUNIER11, PETER M. POTTS12, MAJA ROODBERGEN7,9, HANS SCHEKKERMAN13,
JULIA SCHRÖDER7, EDDY WYMENGA14 & THEUNIS PIERSMA7
1 School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK j.gill@uea.ac.uk
2 Royal Society for the Protection of Birds, The Lodge, Sandy, Beds, SG19 2DL, UK
3 British Trust for Ornithology, The Nunnery, Thetford, IP24 2PU, UK
4 Laboratoire Littoral Environnement et Sociétés, Pôle Sciences et Technologies,
University of La Rochelle, 17042 La Rochelle, France
5 Sociedade Portuguesa para o Estudo das Aves, Av. Liberdade 105, 2º Esq., 1250-140 Lisboa, Portugal
6 Bretagne Vivante – SEPNB, Réserve Naturelle Des Marais De Séné. Brouel Kerbihan- 56860 Séné, France
7 Animal Ecology Group, Centre for Ecological and Evolutionary Studies,
University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands
8 Snæfellsnes Research Centre, University of Iceland, Hafnargata 3, IS-340 Stykkishólmur, Iceland
9 Alterra, Centre for Ecosystem Studies, PO Box 47, 6700 AA, Wageningen, The Netherlands
10 Grupo de Investigación en Biología de la Conservación, Área de Zoología,
Universidad de Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain
11 Ligue pour la Protection des Oiseaux, Corderie Royale, BP90263, 17300 Rochefort, France
12 Farlington Ringing Group, Solent Court Cottage, Chilling Lane,
Warsash, Southampton, Hampshire, SO31 9HF, UK
13 Dutch Centre for Avian Migration and Demography, PO Box 40, 6666ZG Heteren, The Netherlands
14 Altenburg & Wymenga Ecological Consultants, PO Box 32, 9269 ZR Veenwouden, The Netherlands
Gill, J.A., Langston, R.H.W., Alves, J.A., Atkinson, P.W., Bocher, P., Cidraes Vieira, N., Crockford, N.J.,
Gélinaud, G., Groen, N., Gunnarsson, T.G., Hayhow, B., Hooijmeijer, J., Kentie, R., Kleijn, D., Lourenço,
P.M., Masero, J.A., Meunier, F., Potts, P.M., Roodbergen, M., Schekkerman, H., Schröder, J., Wymenga, E.
& Piersma, T. 2007. Contrasting trends in two Black-tailed Godwit populations: a review of causes and
recommendations. Wader Study Group Bull. 114: 43–50.
Keywords: Black-tailed Godwit, Limosa limosa, subspecies limosa, subspecies islandica, population size,
population trend, habitat, conservation
In recent decades, the West European population of Black-tailed Godwits, Limosa limosa limosa, has declined
in size at a quite alarming rate, while the Icelandic population, L. l. islandica, has undergone a rapid increase in
population size. These two populations have been the subject of a great deal of research, much of which has been
focused on understanding the causes and consequences of the contrasting population trends. In 2007, a workshop
was held during the annual conference of the International Wader Study Group at La Rochelle, France, with
the aims of identifying the likely causes of the population changes and providing recommendations for future
actions to improve the conservation of both populations. The available evidence strongly suggests that changes in
productivityasaconsequenceofagriculturalintensicationarethemostlikelydriverofthedeclineinL. l. limosa,
although the concentration of much of the population in just a few sites in winter and spring is likely to exacerbate
their vulnerability to future habitat changes. Agricultural and climatic changes are implicated in the expansion of
L. l. islandica,andtheavailabilityofbothintertidalmudatsandwetgrasslandsasforaginghabitatsappearsto
be very important across much of the winter range of this population. A series of recommendations for actions to
conserve both populations are provided, including improving agricultural land management and protecting key
passage and winter sites and habitats.

Bulletin 114 December 2007
44 Wader Study Group Bulletin
Limosa limosa limosa, provides one of the clearest examples
of this problem. The great majority of this population breed
intheNetherlandswhere,afterincreasinginthersthalfof
the 20th century (Bijlsma et al. 2001), it was a widespread
and common meadow bird in the 1960s, numbering up to
250,000 individuals (Mulder 1972, Piersma 1986). How-
ever, since then this population has declined severely, and
now numbers only around 50,000 breeding pairs (BirdLife
International 2004).
Attempts to reverse this population decline (and similar
declines in many other meadow-breeding bird species) have
focused on implementing agri-environment schemes (AES)
on farmland in breeding areas to improve breeding success
(Beintema et al. 1997, Kleijn et al. 2001, van Brederode &
Laporte 2006, Verhulst et al. 2007). Despite the area covered
by AES aimed at conserving meadow birds increasing from
c.20,000 ha to c.150,000 ha of farmland in the Netherlands
by 2006, and schemes costing in excess of 30 million Euro
per year, no discernible improvement in the population so far
has been apparent (Kleijn et al. 2001). In fact, the national
population trends of meadow birds in the period 2000–2004
have declined even more rapidly (by approximately 3.5%)
than trends in the period 1990–2000 (Teunissen & Soldaat
2006). In addition to agri-environment initiatives, the cre-
ation and management of nature reserves for meadow birds
has also occurred but on relatively small areas (c.18,000 ha,
Schekkerman et al. subm. b). Although population declines
are less steep in reserves than in the wider countryside, there
is much variability between reserves (Teunissen & Soldaat
2006).
By contrast, the population of Black-tailed Godwits that
breeds in Iceland, Limosa limosa islandica, has undergone a
rapid increase over the same time period, from an estimated
2,000–3,000 individuals around 1900 to c.50,000–75,000 at
present. This population has expanded from breeding loca-
tions in south-west Iceland and now occurs virtually through-
out lowland Iceland (Gunnarsson et al. 2005a).
Both the limosa and islandica subspecies of Black-tailed
Godwits have been the subject of extensive research studies in
recent years, mostly focused on the causes and consequences
of population changes (e.g. Beintema 2007, Both et al. 2006,
Gill et al. 2001a, Groen & Hemerik 2002, Gunnarsson et al.
2005b, Roodbergen et al. subm., Schekkerman et al. 2005,
subm. a,b, Schekkerman & Verhulst et al. 2007). In order to
bring together the available information on both populations,
a workshop was held at the International Wader Study Group
conference at La Rochelle, France in 2007. This workshop
aimed to:
ncompare current knowledge of the Icelandic and West
European L. limosa populations
ninform potential explanations for the divergent popula-
tion trajectories
n highlight research gaps and potential future collabora-
tions
nrecommend conservation measures.
Herewereportonthendingsofthisworkshop,particu-
larly focusing on identifying the likely drivers of changes in
demography and distribution of both populations, highlight-
ingthekeyissuesinuencingeachpopulationandproviding
a series of recommendations for future conservation and
research efforts. The workshop attracted c.100 participants
with a wide range of expertise and knowledge of these birds
and their habitats. This meeting was therefore a unique and
exciting opportunity to compare two subspecies with widely
diverging population trajectories, and to discuss causes of
changes and prioritise future actions.
The workshop comprised a series of comparative talks
which detailed current knowledge of the key processes
inuencingbreedingandnon-breedingseasondistribution
and demography, and patterns of connectivity between sea-
sons and sites, for the two populations. During the workshop,
information from each talk was used to complete a summary
table of current status, drivers of change and potential impact
for a series of demographic, distribution and habitat issues
(Tables 1 & 2). The key issues arising from this summary are
discussed below.
CURRENT DISTRIBUTION AND HABITAT USE OF
L. L. LIMOSA
The West European breeding population of Black-tailed
Godwits breeds throughout the Netherlands, with smaller
numbers in Germany, Belgium, Denmark, France and the
UK, and migrates via France and Iberia to winter grounds
in Senegal, Guinea-Bissau and Guinea in sub-Saharan West
Africa (Beintema & Drost 1986, Kuijper et al. 2006).
Key breeding season issues
This population depends on grasslands with high ground-
water levels as breeding sites, and on wetlands as passage
and winter foraging sites (Wymenga et al. 2006). Over the
last 50 years, both of these habitats have undergone extensive
modication.Thecoreoftherecentbreedingrangeofthis
population is on clay-on-peat and peat soils, but the historical
distribution also included blanket bogs and wet moorland,
which were abandoned as the population expanded into agri-
culturalhabitatsinthersthalfofthe20thcentury(Bijlsmaet
al. 2001). Since then, drainage, urbanisation and conversion
of grasslands to arable crops have created drier and highly
fragmented breeding habitats (SOVON 2002). The remaining
grasslands are generally farmed very intensively, with mow-
ing dates having advanced by one month over the last century,
most grasslands now being mown more than twice per year,
and livestock number per unit grassland area being the highest
of all European countries (Statistics Netherlands, Statline).
In addition, there is evidence that changes in predator control
and environmental contamination, and landscape changes
such as road-building and tree-planting, have altered preda-
tor abundance and distribution, and consequently increased
nest and chick predation rates (Schekkerman et al. subm. a,
Teunissen et al. 2006, Teunissen & Willems 2004).
When the population size was higher, godwits bred on
grasslands in areas of peat, clay and sandy soils. The popu-
lation decline has been characterised by a contraction into
largely peat areas, although levels of degradation now appear
similar across all soil types. AES initiatives to reverse the
population decline have focused on delaying mowing dates
and improving nest protection. However, there is no strong
evidence that these schemes have improved breeding densi-
ties (Kleijn et al. 2001, Kleijn & van Zuijlen 2004, Verhulst
et al. 2007, Willems et al. 2004), despite evidence that
delayed mowing saves nests and improves chick survival
(Schekkerman & Müskens 2000, Schekkerman et al. 2005,
subm b). Godwits preferentially choose areas with high
groundwater levels as breeding sites (Kleijn & van Zuijlen

Bulletin 114 December 2007
45
Gill et al.: Contrasting population trends of Black-tailed Godwit subspecies limosa and islandica
2004, Verhulst et al. 2007); although clay soils with relatively
low ground water levels can also be used. Current AES do not,
however, include management of groundwater levels, as this
is a contentious issue for farmers. Successful management
isalsolikelytorequireeldswithtall,openandstructurally
diverse swards within the matrix of more intensively farmed
eldsthroughoutthebreedingseason.Thisprovideschicks
hatched throughout an area with access to high quality forag-
ing sites as well as shelter from predators (Schekkerman et
al. subm. b).
Key non-breeding season issues
On passage and at wintering sites in Iberia and West Africa,
wetlands have been extensively drained and dammed since
the 1960s, to facilitate energy production, water storage and
agriculture (Kuijper et al. 2006). Rice production is now
widespread,andriceeldsprovideanalternativehabitat
which,whenooded,iswetenough toallowbirdssuchas
godwits to forage. Godwits have been reported foraging on
riceeldsinwintersinceatleastthe1970s(Altenburget
al. 1985, Tréca 1984, van der Kamp et al. 2007), and recent
studies of godwits in Iberia and Africa have shown that
the birds primarily consume rice seeds (along with smaller
amounts of invertebrate food) during the months in which
riceeldsareused(Tréca1994).Godwitstypicallyforage
on molluscs, worms and other invertebrates, and the conse-
quences of this largely plant-based diet through much of the
winter and spring are currently unknown.
Godwits begin to arrive in West Africa in July, and they use
riceeldsextensively,particularlyduringplanting(Jul–Aug)
and harvest (Nov–Dec) (Kuijper et al. 2006, van der Kamp
et al.2007).WhentheAfricanriceeldsaredriedoutand
harvested during December, the birds begin to migrate north
tousericeeldsinSpainandPortugal(Sanchez-Guzman
et al. 2007, Zwarts et al. in press). At this time they can be
highlyconcentrated,withupto50,000birdsintheDoňana
National and Natural Park, SW Spain, in December, up to
25,000 in Extremadura, W Spain, by early February and up
to 45,000 around the Tagus and Sado estuaries, W Portugal,
by late February. Passage sites in Morocco were formerly
used in autumn and spring but few birds use these sites
now.DrainageofMoroccanwetlandsmayhaveinuenced
this shift in passage site use, as may recent increases in rice
production in Spain. Similarly, use of French sites on spring
migration may have declined in recent years, although overlap
Table 1. Summary of the current status of the demography, distribution and habitat use of the West European Black-tailed Godwit
population, Limosa limosa limosa, together with likely drivers of changes and estimates of the proportion of the population experiencing these
conditions.
Status of limosa population Drivers of changes Potential population
impact
Population size c.60,000 breeding pairs
Population trend Severe decline at c.5%p.a. Primarily due to declining productivity Population-wide
Nest survival Intermediate to low and variable. Earlier mowing and increased predation Population-wide
Chick survival Low. Declines since 1980s Earlier mowing, reduced habitat heterogeneity and
increased predation
Population-wide
Productivity trend Decline since 1980s from c.0.7 to 0.2
edgedyoung/pair
Lossofgrasslandswithhighwatertables,intensication
of remaining grasslands
Population-wide
Juvenile survival Estimates from 40% to 68% Huntingofjuvenilesonmigrationcouldbesignicant Higher estimate from one
site only (Workumerwaard)
Adult survival Annual estimates = 81–96% Unknown Probably population-wide
Breeding habitat Grasslands with high ground water levels
in open landscapes
26% loss to urbanisation and arable conversion since
1960s. Severe decline in quality through drainage and
intensication
Population-wide
Breeding locations Grassland in Netherlands, Germany,
Belgium and Denmark
Unknown as degradation of all soil types appears similar Population wide
Breeding trend Declining and contracting in range Declining habitat quality, fragmentation Population-wide
Autumn habitat Wetlands,mudats,saltpans,riceelds Unknown Unknown
Autumn locations France (Jun–Nov), Iberia (Jun–Nov) and
W Africa (Jul–Nov)
ReducedwetlandareainMoroccoandSEuropeand/or
changes in site quality
Mostadultsydirectto
Africa. Juveniles may use
European sites
Autumn trend Earlier departure and reduced use of
Morocco
Early departure correlated with poor breeding success
and deferral of breeding
Unknown
Winter habitat Riceeldsandwetlands Increased use of rice following widespread conversion
of wetlands
Population-wide
Winter locations Senegal and Guinea Bissau (Nov–Dec),
Iberia (Dec–Feb)
Large-scale damming, drainage, water storage and
agriculture in Senegal delta
Population-wide
Winter trend Possible earlier departure from Africa for
Iberia
Departurefollowsdryingofriceelds–
changing rainfall patterns may be involved
Population-wide
Spring habitat Riceelds,saltpansandwetlands Conversionofwetlandstoriceelds Population-wide
Spring locations Iberia (Dec–Feb), France (Feb–Mar) and
Netherlands (Mar–Apr), reduced use of
Morocco and France
ReducedwetlandareainMoroccoandFranceand/or
changes in site quality
Switch to rice-seed diet
Population-wide
Spring trend Possible earlier departure from Iberia but
arrival in Netherlands unchanged
Unknown Unknown

Bulletin 114 December 2007
46 Wader Study Group Bulletin
between the two subspecies at this time of year makes this
difculttoassess.
POSSIBLE CAUSES OF THE POPULATION
DECLINE IN L. L. LIMOSA
These extensive habitat changes throughout the range of
L. l. limosa allow several plausible causes of the severe
populationdeclinetobeidentied:
n declining habitat quality and availability in the breeding
season may have resulted in reductions in productivity;
nchanges in winter and spring diet may have altered the
body condition or survival probability of fully-grown
birds;
nhabitat and climatic changes in the Sahel region may have
altered habitat availability, and consequently body condi-
tion or survival of fully-grown birds.
The demographic evidence presented at this workshop strong-
ly suggests that reductions in productivity are the most likely
driver of the population decline. Changes in productivity
through the period of breeding habitat change have been
severe, declining from c.0.7 chicks per pair (range: 0.5–1) in
the 1980s to c.0.2 chicks per pair (range: 0.1–0.7) at present
(Schekkerman et al. 2005, subm b). Changes in the timing
and frequency of mowing, affecting both direct nest and chick
losses and the foraging conditions for chicks (Schekkerman
& Beintema 2007), are strongly implicated in driving these
declines. In addition, the abundance of nest and chick preda-
tors and their impact on an increasingly fragmented and
exposed (through loss of cover by early mowing) population
appears to be growing. In recent years, there has also been
evidence from one site for deferral of breeding by up to half
of the adults returning to the breeding grounds.
The widespread use of rice as food in winter and spring may
affect adult body condition but there is currently no evidence
for any declines in adult survival rates, in fact adult survival
appears to have increased in recent decades (Zwarts et al. in
press). Recent colour-ring studies suggest high adult annual
survival rates of c.81–96% (Both et al. 2006, Roodbergen et
al. subm., J. Schröder in prep.), though national estimates
from ring-recoveries suggest annual survival rates of c.80%
(van Noordwijk & Thomson subm.). Recent reductions in
the length of the hunting season in France are likely to have
reduced hunting pressure, and numbers of hunting recoveries
of ringed birds have declined in recent years (Zwarts et al.
in press). Mortality of juveniles on autumn migration may
Table 2. Summary of the current status of the demography, distribution and habitat use of the Icelandic Black-tailed Godwit population, Limosa
limosa islandica, together with likely drivers of changes and estimates of the proportion of the population experiencing these conditions.
Status of islandica population Drivers of changes Potential population impact
Population size c.50,000–75,000 individuals
Population trend Rapid increase, from c.2600 around 1900 Warmer temperatures and agricultural
expansion in Iceland
Population-wide
Nest survival 50–75% of nests hatch Unknown Unknown
Chick survival 20–80%pairsedgeatleastonechick.
Productivity likely to be c.0.5–0.8chicks/pair
Population expansion may have reduced
average productivity
Unknown
Productivity trend Unknown Unknown Population-wide
Juvenile survival c.60%fromringingtoedgingandc.50%
post-edgingtorstautumn
Unknown Population-wide
Adult survival Annual estimates = 87–99%, highest in winter
and lowest during spring migration
Survival increased in late 1990s.
Some evidence of recent declines
Probable regional variation in
survival trends
Breeding habitat Lowland marshes and dwarf-birch bogs Suitability of dwarf-birch bogs as breeding
sites may have increased
Population-wide
Breeding locations Expansion from SW to NE Iceland Expansion into colder parts of Iceland with
more dwarf-birch bog
Population-wide
Breeding trend Increasing and expanding distribution Average productivity likely declined but
number of pairs increased
Population-wide
Autumn habitat Estuarinemudats,occasionaluseofriver
valleys and gravel pits
None Most use of freshwater habitats by
juveniles
Autumn locations Most in UK, Ireland and France (Jul–Sep). None Population-wide
Autumn trend Expansion into E and NW England moulting
sites
Population size increase c.30% of population in new sites
Winter habitat Estuarinemudatsandgrasslands.
Saltpans in Iberia
Grassland use more extensive in recently
occupied sites
c.80%onmudatsandc.20% on
grasslands
Winter locations UK, Ireland, France and Iberia (Oct–Feb) Population size increase Population-wide
Winter trend Recent expansion into E and NW England Population size increase c.10% of population in new sites
Spring habitat Estuarinemudatsandgrasslands.Someuse
ofsaltpans(France&Iberia)andriceelds
(Iberia)
Grassland use more extensive in recently
occupied sites
c.30%onmudatsandc.70% on
grasslands
Spring locations Netherlands (Iberian and French birds),
Ireland (Irish birds), UK (UK and Irish birds)
(Mar–Apr)
Increase in use of Netherlands and E England
grasslands
c.50–60% of the population uses
Netherlands and E England sites
Spring trend Increasing use of grasslands on spring passage.
Earlier arrival in Iceland
Changingrainfall.Populationincreaseand/or
warmer springs
Earlier arrival trend may be more
apparent in the earliest birds

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Gill et al.: Contrasting population trends of Black-tailed Godwit subspecies limosa and islandica
be higher as they appear to use European passage sites more
than adults, and may thus be exposed to hunting pressures in
France. The available national ringing recovery data, together
with a recent colour-ringing study from one site, suggest that
juvenile survival is not particularly low, but these estimates
may not be representative of the whole population.
Habitat structure and composition in Iberia and West Africa
have clearly changed dramatically since the 1950–1960s,
especially in the Senegal delta, but again there is little evi-
dence for negative impacts on survival rates, at least in recent
years. Mortality rates do appear to be a little higher in years
with low rainfall in the Sahel, possibly as a consequence of
birds occurring at high densities in the remaining wet areas,
especially during the post-breeding arrival period when con-
ictwithricefarmerscanmakethegodwitsvulnerableto
hunting pressure (Zwarts et al. in press). However, although
there is no strong evidence for climatic or habitat changes
in the non-breeding season driving the population declines,
there is clear concern that these processes could exacerbate
the declines, as such a high proportion of the population is
dependentuponrelativelysmallareasofriceeldsatkey
times of year.
CURRENT DISTRIBUTION AND HABITAT USE OF
L. L. ISLANDICA
The Icelandic population of Black-tailed Godwits breeds pri-
marily in Iceland, with small numbers in the Faeroes, Lofoten
and Shetland Islands. In Iceland they breed in lowland areas,
primarily on coastal marshes and dwarf-birch bogs (Gunnars-
son et al. 2006a).
Key breeding season issues
In both marshes and dwarf-birch bogs, Icelandic Black-tailed
Godwits are strongly associated with shallow pools, often
surrounded by sedges, which support foraging adults. Chicks
feed mostly on invertebrates gleaned from vegetation, and
seek out tracts of grassland which are rarer in the dwarf-birch
bog habitats. The expansion from SW Iceland (around 1900)
to the major basins in the north and west (1920s–1940s) and
then the east and north-east of Iceland (1970s–1980s) was
characterised by an increase in the proportion of dwarf-birch
bog sites occupied (Gunnarsson et al. 2005a). The most
recently occupied sites are also colder than the traditionally
occupied southerly sites (Gunnarsson et al. 2006b). The
lowland areas of Iceland have seen widespread drainage of
wetlandsandincreasesinnumbersofhayeldssincethe
1960s, and godwits are now frequently recorded feeding on
hayeldsduringthebreedingseason.
Key non-breeding season issues
After the breeding season, Icelandic godwits migrate south
to the UK, Ireland and France. Small numbers of birds also
appear to migrate directly to Portugal from Iceland. The
moulting sites in the north-west and east of England have
seen particularly large increases in use in recent decades,
especially the Wash, Humber and Dee estuaries. The vast
majorityofIcelandicgodwitsuseestuarinemudatsduring
the autumn months. By winter many birds have moved
south to estuaries in France and Portugal and, in Ireland and
England, they start to forage on grasslands. The number of
Icelandic godwits wintering in the UK, Ireland and France is
wellreported,butthenumberwinteringinIberiaisdifcult
to assess because the subspecies overlap there, particularly
during January and February when both wintering and migra-
tory continental godwits are present.
In spring, most godwits from Portugal and France migrate
to the Netherlands or eastern England, where they forage
primarily on grasslands. At the same time, many birds from
coastalsitesaroundtheUKmoveinlandtoforageonooded
grasslands.Studiesofenergeticintakeratesonmudatsand
grasslands suggest that godwits move to grasslands when
estuarinefood suppliesarenolongersufcienttosupport
them,andthattheyfrequentlyusebothmudatsandgrass-
lands throughout winter and spring. This seems to be par-
ticularly common in the northern part of their range, where
estuarine prey are often subject to strong seasonal depletion
(e.g. Gill et al. 2001b) and where grassland foraging appears
to be a necessary addition to compensate for insufficient
estuarine food supplies.
POSSIBLE CAUSES OF THE POPULATION
INCREASE IN L. L. ISLANDICA
The drivers of the population increase in Icelandic god-
witsarenotfullyidentied,butthereareseveralplausible
candidates:
nclimatic amelioration in Iceland may have improved
breeding conditions and increased the area available for
breeding godwits;
nchanges in habitat structure in Iceland may have improved
breeding conditions;
nclimatic and habitat changes in the non-breeding range
may have improved survival and condition for breed-
ing;
nchanges in hunting pressures may have improved survival
rates.
The initial increase in godwit numbers around the 1920s co-
incided with a period of rapid warming in Iceland, suggesting
that climatic amelioration may have been involved, at least in
the early stages of population growth. From the 1930s to the
1980s, the rate of colonisation of Iceland is correlated with
the number of drainage ditches installed, indicating that large-
scalehabitatchangesmayhavepositivelyinuencedgodwit
breeding distribution. The common observation of godwits
foraginginhayelds,especiallythoseclosetodwarf-birch
bogs, suggests that the presence of hayfields as foraging
habitats may have improved the quality of dwarf-birch bogs
as breeding sites.
In recent decades, the primary habitat change in lowland
Iceland has been the development of afforestation schemes,
many of which are focused on marsh habitats, in addition to
house-building in lowland areas. Since the 1980s, there has
been a strong positive correlation between Iceland spring
temperatures and the index of Icelandic godwits wintering
in the UK (as recorded by the Wetland Bird Survey, Banks
et al. 2006). Colour-ring information has shown that the
majority of the UK population increase has involved birds
from the recently occupied east and north-east of Iceland
(Gunnarsson et al. 2005b); strongly suggesting that recent
climatic amelioration has allowed these coldest parts of the
country to be occupied.
In the non-breeding range, there are few indications of
improvements to habitat quality, but changing rainfall pat-

Bulletin 114 December 2007
48 Wader Study Group Bulletin
terns may be altering the timing of availability of grassland
foraging sites. This may be particularly true of sites in eastern
England and the Netherlands, use of which has increased
substantially in recent years (Gerritsen & Tijsen 2003, Gill
et al. 2001). The reduced frequency of cold winters in NW
Europealsomaybeinuencingsurvivalrates.
The role of hunting pressure in driving population changes
inIcelandicgodwitsisdifculttoassess.Historically,there
are records of godwits being considered a delicacy, having
been described as “highly esteemed for the table” and “both
shot and taken by snares” (Morris 1897). It is possible that
reductions in hunting pressure, and the associated disturbance
levels, may have influenced the population changes, but
there are currently no data with which to explore this issue.
At present, the only country in which Icelandic godwits are
shot is France, and the lack of accurate bag statistics precludes
calculation of the impact of this hunting pressure. Although
the Icelandic population is increasing, it is still small and
restricted in range, and the impact of hunting is therefore
difculttopredictshouldconditionschange.
CONTRASTING LIMOSA AND ISLANDICA
POPULATIONS
Despite the current contrast in the fortunes of these two popu-
lations, comparison of their demography and distribution has
revealed intriguing similarities, which we hope will help to
focus current and future conservation and research efforts. In
both Iceland and the Netherlands, it seems evident that agri-
culturalintensicationhasplayedaroleindrivingpopulation
expansions and contractions over the last century. Wetlands
and heathlands have been converted into agricultural habitats
in which productivity has increased through fertilisation and
reductionofoodingintensity,whilefrequentcuttingand
mowing maintains an open sward structure. This seems to
havebenetedseverallarge,ground-nestingshorebirdspe-
cies, probably through higher abundances of soil macrofauna
and improved access to these resources (Beintema 1986,
Beintema et al. 1987). Throughout Europe this process began
inthersthalfofthetwentiethcentury,butsofarthearea
convertedandthelevelofintensicationhavebeenmuch
greater in the more populated countries of NW Europe than in
Iceland. In both Iceland and the Netherlands, there is evidence
that populations of Black-tailed Godwit, along with other
similar species, may have been able initially to increase and
expand their distribution in response to this habitat conversion
and increase in productivity.
In the Netherlands, the agricultural landscape is now so in-
tensively managed that the area suitable for breeding godwits
has declined dramatically, such that the population is now
probably lower than it was prior to the 1950s. By contrast,
theIcelandicpopulationappearstobestillbenetingfrom
changes in agricultural practice that have created a landscape
in which grass production and moderate levels of horse graz-
ing have given rise to the complex sward structure necessary
for breeding, alongside areas suitable for foraging. The extent
to which these habitat changes have driven the population
increase in Iceland is not currently clear, and there may yet
be scope for further population expansion in Iceland. How-
ever, the Netherlands experience would strongly suggest that
furtherintensication,suchasincreasinggrazingintensities,
are likely to be very detrimental to godwits and other ground-
nesting birds. In addition, land-use changes in Iceland, such as
the current widespread afforestation programmes, are a major
threat to the internationally important shorebird populations
of lowland habitats.
While habitat changes may be the primary driver of popu-
lation changes over the last century, climatic changes have the
potential to be an equally important issue in the near future.
Temperature increases and changing precipitation patterns are
both implicated in the islandica population increase, and there
is some recent evidence for deferral of breeding in limosa
in particularly dry years, although warm conditions are also
likely to improve chick growth and survival. The timing of
spring rainfall and the magnitude of temperature changes in
the future are therefore likely to be very important in deter-
mining the impact of climate change on breeding success. The
dependence of most of the limosa population on relatively
smallareasofoodedriceeldsinAfricaandIberiaisalso
likely to make them highly vulnerable to changing rainfall
patterns. The recent drought in the Sahel region (Dai et al.
2004) is of particular concern for the maintenance of suitable
foraging areas for these birds. Rice production is also depen-
dent upon global markets and, in Iberia, on European Union
agricultural support mechanisms, further increasing concern
over the persistence of these key habitats.
A more immediate threat to the godwits that depend on rice
eldsandmudatsinPortugalistheproposeddevelopment
of a new airport near Lisbon. One potential location for this
airport is in the vicinity of the Tagus Estuary Nature Reserve,
withapproachroutesthatarelikelytocrossthemainriceeld
areas in the Tagus and Sado estuaries, which are used by tens
of thousands of godwits during January and February, and
thecorridorlinkingtheTagusandSadomudatswhichare
used by godwits throughout the non-breeding season. Such a
development could seriously impact on a very large propor-
tion of the godwit population at a critical time of year, and
would therefore be very likely to exacerbate already severe
population declines.
The historical context of the population changes, and
concern about future conditions for godwits and other similar
bird species, led the workshop participants to identify the
key recommendations that we believe it will be necessary
to implement in order to conserve Black-tailed Godwits
effectively in Iceland and W Europe.
CONSERVATION RECOMMENDATIONS
FOR L. L. LIMOSA
1. Improve prescriptions and targeting of AES in the breed-
ing range, focusing efforts in areas with high groundwater
levels and open landscapes to attract godwits and avoid
high predator densities, in order to have the potential to
improve overall productivity. Include raising groundwater
levels in the Netherlands AES prescriptions (as is the case
in the UK, Denmark and Germany)
2. Incorporate the creation of small-scale habitat mosaics
into management prescriptions, to provide both foraging
and predator avoidance options throughout the season.
3. Improve conservation of key wetland habitats in Iberia
and Africa, either through maintenance of support for rice
production or restoration of wetlands, as well as designa-
tion of more sites under relevant national legislation and
international treaties (EU Birds and Habitats Directives,
Ramsar Convention etc.).
4. In view of the severe continuing declines of this population,
take a precautionary approach and ban hunting of godwits,
at least temporarily, where there is any risk that birds from

Bulletin 114 December 2007
49
Gill et al.: Contrasting population trends of Black-tailed Godwit subspecies limosa and islandica
this population could be involved (especially late migrat-
ing juveniles in autumn), until productivity is increased
to a level that can sustain a certain amount of additional
mortality of adults and immatures.
CONSERVATION RECOMMENDATIONS FOR
L.L. ISLANDICA
1. Improve conservation of winter habitat mosaics, particu-
larly in areas, such as Ireland, England and France, where
grasslands, coastal lagoons and salinas may be necessary
to maintain populations when estuarine food supplies are
depleted.
2. Reduce impact of afforestation and building developments
in Iceland on godwits and other shorebird species, by
conserving key breeding areas.
3. Improve protection of coastal habitats in areas where
development and associated disturbance levels are high
(especially in Ireland).
KEY RESEARCH GAPS FOR L. L. LIMOSA
1. Improve estimates of juvenile survival, causes of mortality
and distribution prior to recruitment.
2. Improve survey information on the distribution and
abundance of Black-tailed Godwits in the West African
wintering grounds.
3. ImproveunderstandingoftheimportanceoftheDoňana
National and Natural Park area for protecting L. l. limosa
during spring migration.
4. Explore the potential impact of hunting on the limosa
population, and work with hunting organizations to
develop better methods of recording accurate bag statistics
in France.
5. Explore the impact of the increasing time-lag between
godwit arrival in the Netherlands and the commencement
of breeding, and the frequency of deferral of breeding
attempts.
6. Improve understanding of the location, timing and dura-
tion of use of passage sites in Europe and Africa, and
habitat use and diet within these sites.
KEY RESEARCH GAPS FOR L. L. ISLANDICA
1. Improve understanding of the role of agricultural intensi-
cationinIceland.
2. Identify the key drivers of productivity in different habi-
tats in Iceland.
3. Improve survey data for Iberia and France during the
passage period of January to March, when there is the
greatest overlap between the subspecies.
4. Explorethefactorsinuencingthequalityandavailability
of grassland habitats.
5. Explore the consequences of seasonal matching (indi-
vidual use of similar quality habitat in both breeding and
winteringareas)forpopulationprocessesandidentica-
tion of key areas for conservation.
6. Explore the potential impact of hunting on the islandica
population.
FINAL COMMENT
The workshop provided an exciting and hopefully very valu-
able means of exploring the causes of population change in
two closely related subspecies. The large group of experts
provided an ideal forum for both highlighting key issues
and using expert opinion to identify and prioritise the con-
servation recommendations. This process would undoubt-
edly have been helped were information available on the
eastern population of L. l. limosa and the eastern subspecies,
L. l. melanuroides.Ournalrecommendationisthereforeto
encourage the collation and presentation of information on
these two populations.
ACKNOWLEDGEMENTS
Many thanks to all the workshop participants who contributed
so willingly and helpfully to the whole day, Bill Sutherland
for historical godwit recipes, Richard Chandler for helpful
comments and to the organising committee of the IWSG
conference for providing such excellent conditions for eating,
drinking, colour-ring reading and discussion.
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