Journal of Applied Ecology 2008, 45, 1067–1075
doi: 10.1111/j.1365-2664.2008.01506.x
The effect of ‘mosaic management’ on the demography
of black-tailed godwit Limosa limosa on farmland
Blackwell Publishing Ltd
Hans Schekkerman1*, Wolf Teunissen2 and Ernst Oosterveld3
1
Dutch Centre for Avian Migration and Demography, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 40, 6666 ZG
Heteren, The Netherlands; Alterra, Wageningen University and Research Centre, Wageningen, The Netherlands; Animal
Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14,9750 AA Haren, The
Netherlands; 2SOVON Dutch Centre for Field Ornitology, Rijksstraatweg 178, 6573 DG Beek-Ubbergen, The Netherlands;
and 3Altenburg & Wymenga Ecological Consultants, PO Box 32, 9269 ZR Veenwouden, The Netherlands
Summary
1. Like many farmland birds, the largest European population of the black-tailed godwit Limosa
limosa, in The Netherlands, has been declining for decades despite conservation measures including
agri-environment schemes (AES). In a new experimental AES aiming to reverse this decline,
collectives of farmers implemented spatially coordinated site-level habitat management (‘mosaic
management’) including delayed and staggered mowing of fields, refuge strips and active nest
protection.
2. We evaluated the effectiveness of mosaic management by measuring godwit breeding success in
six experimental sites and paired controls. Productivity was higher in mosaics than in controls due
to fewer agricultural nest losses. Chick fledging success was poor in both treatments. Productivity
compensated for adult mortality in only one AES site.
3. Although creating chick habitat was a major management goal, the availability of tall grass
during the fledging period did not differ between treatments, mainly because rainfall delayed
mowing in all sites and study years. However, chick survival increased with the availability of tall
grass among sites. Higher chick survival will thus enhance the positive effect of mosaic management
in drier years, but sensitivity to weather represents a weakness of the AES design.
4. Available estimates of productivity in Dutch godwits suggest a strong reduction over the past 20
years and implicate chick survival as the main driver of their decline. Earlier mowing of grassland
is the main causal mechanism, but changes in vegetation structure and composition, and increased
predation may also have contributed.
5. Synthesis and applications. Demographic rates like breeding success are useful parameters for
evaluating effects of management. Mosaic management increases the productivity of black-tailed
godwits, but does not ensure long-term population viability for this flagship species of wet grassland
bird communities. More stringent management prescriptions need to improve both the area and the
quality (vegetation structure) of grassland mown late. Management efforts should be concentrated
in areas with favourable pre-conditions in order to improve overall effectiveness.
Key-words: agri-environment scheme, grassland birds, chick survival, breeding productivity,
conservation, mowing date
Introduction
Throughout Europe, biodiversity is declining in agricultural
landscapes (Donald, Green & Heath 2001; Benton et al. 2002;
Flade et al. 2006) including lowland wet grasslands which
form the habitat of a formerly rich and diverse breeding bird
*Correspondence author. E-mail: h.schekkerman@nioo.knaw.nl
community (Beintema, Dunn & Stroud 1997; Wilson, Ausden
& Milsom 2004). Negative effects of agricultural intensification
on the birds’ reproductive output are generally considered to
be the main cause of these declines (Vickery et al. 2001;
Newton 2004).
The Netherlands encompasses a large expanse of wet
grassland devoted to intensive dairy farming and holds internationally important populations of grassland shorebirds.
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
1068
H. Schekkerman, W. Teunissen & E. Oosterveld
This includes 47% of the European population of black-tailed
godwit Limosa limosa Linnaeus, a species listed as globally
near-threatened (IUCN 2007). The Dutch population declined
from > 125 000 breeding pairs around 1960 to c. 62 000 in
2004, of which 60–75% breed in agricultural grasslands
(SOVON 2002; Teunissen & Soldaat 2006). Reduced breeding
productivity has been implicated as the main cause of this
decline (Kruk, Noordervliet & ter Keurs 1997; Schekkerman
& Müskens 2000).
Conservation measures for ‘meadowbirds’ in The Netherlands have included (i) reserves where biodiversity takes
priority over agricultural production (currently c. 18 000 ha),
(ii) Agri-Environment Schemes (AES) reimbursing farmers
for less intensive field use (27 000 ha) and for protecting
shorebird clutches during farming operations (123 000 ha),
and (iii) similar nest protection by volunteers and unpaid
farmers (c. 200 000 ha; Musters et al. 2001; van Paassen 2006).
In 2005, AES received 87% of the $31 million national budget
for meadow bird conservation.
Management prescriptions of existing AES focus on postponement of cutting and grazing of individual fields, usually
until 1–15 June. This reduces destruction of eggs and chicks
(Beintema & Müskens 1987; Kruk, Noordervliet & ter Keurs
1997) and increases the availability of chick foraging habitat
(Schekkerman & Beintema 2007). As godwit broods migrate
towards unmown fields, this may also enhance the productivity
of pairs breeding in the surrounding area. However, most
existing studies have failed to show positive effects of AES on
shorebird breeding densities (Kleijn et al. 2001; Kleijn & van
Zuijlen 2004; Verhulst, Kleijn & Berendse 2007). Because the
effects on breeding productivity were not investigated in these
studies, the possibility remains that AES lead to more fledged
chicks but these settle outside the managed sites. However, it
is clear that existing AES have not halted the countrywide
decline of black-tailed godwit and other grassland birds
(Teunissen & Soldaat 2006).
Acknowledging the importance of farmland for godwits
and the need for spatially coherent management (Whittingham
2007), Dutch conservation organizations designed a new
AES to optimize breeding conditions for black-tailed godwits
within the constraints of modern dairy farming. In this
scheme, collectives of farmers coordinate field use at the site
level to provide sufficient foraging habitat for chicks and
create spatial heterogeneity providing resources for all age
classes of godwits (and other meadowbird species) within
reachable distance throughout the breeding season (Benton,
Vickery & Wilson 2003). ‘Mosaic management’ was put into
practice for 3 years in six experimental sites to investigate its
feasibility and conservation performance.
This study evaluated the effect of mosaic management
on breeding output of black-tailed godwits. We focused on
productivity for three reasons. First, it is the demographic
variable that the AES aims to increase. Secondly, breeding
output may respond to management immediately, while
observing an increase in density within a few years is less
likely in a long-lived species like black-tailed godwit. Thirdly,
productivity provides a direct measure of the contribution of
management to the wider population while density effects
may be confounded by dispersal in addition to local breeding
success.
We tested two criteria of AES effectiveness: (i) productivity
should be increased in areas subject to the management
prescriptions, and (ii) productivity should at least balance adult
mortality in AES sites so that the population is sustainable.
Productivity should be approximately 0·6 fledged young per
breeding pair (Schekkerman & Müskens 2000). Based on our
study and previous productivity estimates, we discuss the
outlook for conservation of black-tailed godwits in modern
farmland.
Methods
EXPERIMENTAL AGRI-ENVIRONMENT SCHEME
Mosaic management was established at six lowland wet grassland
sites in The Netherlands during 2003–2005. Sites were selected on
the basis of willingness to cooperate among farmers and the presence of reasonable numbers of breeding godwits. At each site, 6–10
farmers participated in an area of 215–334 (mean 281 ± SD 53) ha.
Within most sites, some land was owned by non-participants
(9 ± 9%). One site included part of a meadowbird reserve (4%) and
two bordered on reserves. Table 1 lists the practical components of
the AES, their rationale, and area contracted. Mosaics were designed
to offer ≥ 1 ha of preferred grassland (sward height ≥ 15–20 cm,
Schekkerman & Beintema 2007) per godwit brood throughout the
chick-rearing period, based on previously observed maximum
brood densities (Schekkerman, Teunissen & Müskens 1998). Field
use was spatially coordinated to allow all broods to reach suitable
grasslands within a few 100 m distance.
STUDY DESIGN
Each of the six experimental AES sites was paired with a control site
(223 ± SD 118 ha). Selection criteria for control sites were proximity
to the AES site (0–5 km, mean 2·2 ± 2·4 km), similarity in landscape,
field size and shape, and water level, and the presence of > 20 godwit
pairs. Some control sites included a few fields under other AES
contracts. Nest protection was employed on nearly all fields in five
AES sites and on about 50% in the sixth; it was nearly complete in
three, partial in two, and absent in one of the control sites. Average
godwit territory densities were 27·5 ± SE 4·5 km−2 in experimental
sites and 19·0 ± 3·7 km−2 in controls.
Breeding productivity was measured in 1 year in each AEScontrol pair, and two site pairs were studied per year. One site pair
was studied both in 2004 and 2005; results were averaged where
appropriate. In one control site, we failed to estimate productivity
as volunteers stopped marking clutches in response to the presence
of a red fox Vulpes vulpes Frisch. As this was probably unrelated to
management, excluding this site will not have biased the results.
Measuring breeding productivity (B, fledged young per breeding
pair) is difficult in nidifugous birds like godwits, as broods move
around and often remain hidden in vegetation. We combined data
on hatching success of the majority of nests in the study area with
chick survival in a sample of radio-tagged broods to estimate productivity as: B = U × [1 + (V × (1 − U)] × L × K, where U = probability
that a clutch survives to hatching, V = probability that a failed
clutch is replaced (0·5, based on Schekkerman & Müskens 2000),
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Improving breeding success of black-tailed godwits 1069
Table 1. Components of the mosaic management AES with rationale and average proportion of area contracted in the six experimental sites
Management component
Rationale
%
First cut postponed until 1 or 8 June
First cut postponed until 15 or 22 June
Grazing followed by rest until 15 June
Sequentially mowing out strips to feed to cattle in stable
Leaving uncut strips at early-cut fields
Chick-feeding habitat and shelter
Chick-feeding habitat and shelter
Chick-feeding habitat in late spring
Diverse sward height within field, suitable for foraging adults and chicks
Escape havens during mowing; feeding habitat and shelter during brood
movements
Allow broods to find unmown grass nearby when field of residence is cut
11
7
4
4
2
No specific conservation rationale
Early-season resting and feeding habitat for adults
Avoid agricultural egg losses due to mowing or trampling
13
1
86
More chicks able to escape machines
86
First cut in May staggered in three tranches separated by
≥ 1 week
Grazing
Flooding grassland, 15 February to 15 April or 15 May
‘Nest protection’; marking and mowing around clutches
or placing nest protectors over nests
Reduced driving speed during mowing
L = number of eggs hatched per successful clutch, and K = probability
that a chick survives to fledging.
FIELD METHODS
Volunteers, farmers and researchers located the majority of godwit
nests in the study sites (usually > 80%, judged from territory counts),
and marked them with sticks at 1–3 m distance. Hatching dates were
predicted by floating eggs in water. Nest survival was monitored
through repeated visits at intervals from several days to 2 weeks.
Some volunteers recorded only whether nests were successful (≥ 1 eggs
hatched; eggshell fragments present), but in 63% of 364 successful
nests, the number of remaining eggs was recorded, and hence, by
subtraction from clutch size, the number of chicks hatched was
obtained.
Chick survival was estimated by radio-tagging one parent or the
chicks themselves in 5–20 (11·5 ± 5·2) broods per site. Adult godwits
were trapped on the nest during late incubation or on newly hatched
young, individually colour-ringed and fitted with small radio transmitters as described in Warnock & Warnock (1993). Transmitters
(BD-2, Holohil, Canada/Microtes, The Netherlands) weighed 3 g
(0·9–1·3% of body mass) and signals ranged from 0·5 to 1 km on the
ground and up to 2 km in flight. Chicks were tagged at hatching
(71% of N = 226, usually two chicks per brood of four) or at a later age,
using smaller transmitters (LB-2, Holohil/Microtes, 1·0 g, 0·5–3·5%
of body mass) with a range of 50–300 m depending on the chicks’
position and behaviour.
When godwits are approached by observers, diagnostic alarm
calls and behaviour show reliably whether living chicks are present,
but it was often impossible to count chicks in the tall grass. However,
around the fledging age (c. 25 days), chicks more often leave cover
and they are guarded by a parent until 30–33 days old, allowing the
number of fledged young to be established. For the single successful
tagged parent of which we did not know how many chicks fledged
(one out of 14), we used a mean for known broods (1·5, Schekkerman
& Müskens 2000).
Tagging parents does not yield insight into the causes of chick
deaths, which is important for interpreting variation in breeding
success. Therefore, in 2004 and 2005, we tagged the chicks themselves, so that dead chicks could be recovered. In 2004, only chicks
were tagged. Although most chicks whose radio signal disappeared
before the fledging age were recovered dead, 22% were not, leaving
doubt about their fate (dead, tag failure, or moved beyond the
search range). In 2005, both a parent and two chicks were tagged in
58
the focal broods. This greatly facilitated determining their fate, as
adults could be located from greater distances and their behaviour
observed after their chicks’ signal was lost. This confirmed that all
49 ‘missing’ chicks had died; their parents stopped alarming before
the fledging age, except in one case where a tag-less sibling survived.
In addition, from the number of tagged and tag-less chicks fledged
within each brood, we confirmed that chick survival was not reduced
by tagging (Schekkerman, Teunissen & Oosterveld in press).
Broods were relocated every 1–4 days. The presence of living
chicks was deduced from their parents’ behaviour or from fluctuations
in the strength of chick radio signals, indicating movement. Chicks
were recaptured every 4–7 days to check transmitter attachment and
weigh the birds. Missing signals were searched throughout the study
area as well as in woodland potentially containing predators’ haunts
up to c. 5 km away. We also used a metal detector to search under
known nests of grey heron Ardea cinerea Linnaeus and raptors up to
10 km from the study site. Causes of death were deduced from the
state and location of chick remains.
The agricultural use of all fields in the study areas was recorded at
least weekly. The availability of suitable chick habitat was calculated
from these data as: %(chick grass) = %(uncut grassland) + 0·7 ×
%(regrowth) + 0·5 × %(refuge strips + strip mowing). All these
swards were ≥ 15–20 cm high; ‘regrowth’ refers to fields cut or
grazed earlier in the spring. Weighting factors reflect the proportion
of fields covered by tall grass and its suitability as chick habitat
(Schekkerman, Teunissen & Müskens 1998). Uncut grassland made
up the majority of ‘chick grass’ (64 ± 39%).
STATISTICAL ANALYSES
Hatching success was calculated from daily clutch survival probabilities (Aebischer 1999), assuming a total exposure of 25 days. For
broods with a tagged parent, chick survival was calculated as the
number of chicks fledged (day 25) divided by the number of eggs
hatched. Survival of tagged chicks without a tagged parent (2004)
was estimated with the Kaplan–Meier estimator (Kaplan & Meier
1958), as several chicks were tagged when ≥ 1 day old and others lost
their tag. Maximum and minimum estimates were made by treating
chicks that remained ‘missing’ as either dead or censored from the
day their radio signal was lost. In 2005, we ascertained that all ‘missing’
chicks died before fledging, but as broods without a tagged parent
may be more easily missed during searches and predation seemed
more severe in 2005; this result may not be directly applicable to
2004. However, as most missing chicks probably died, minimum
© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Applied Ecology, 45, 1067–1075
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H. Schekkerman, W. Teunissen & E. Oosterveld
estimates were given five times greater weight than maximum estimates.
Standard errors for productivity were obtained by bootstrapping,
resampling from the probability distributions for the number of
chicks hatched per successful clutch (normal distribution), clutch
survival (beta distribution), and chick survival (beta distribution).
The effect of AES management was evaluated by pairwise tests,
comparing the availability of brood habitat, clutch survival, chick
survival and productivity between experimental and nearby control
sites with analysis of variance, using ‘site pair’ as a blocking factor.
To take into account differences between sites in the precision of
productivity estimates, these were weighted by the reciprocal of
their coefficient of variation.
The relationships between breeding parameters and the availability
of chick habitat were tested by linear regression of the site estimates
on the average proportional area of unmown grassland or ‘chick
grass’ during the main chick period. The latter was defined for each
site as running from the date when 25% of all local clutches had
hatched to 25 days after the date when 75% had hatched. Median
hatching dates differed between sites by up to 4 weeks.
We calculated an index of chick condition at each capture (2004
and 2005 only) by dividing body mass by the mass predicted at the
chick’s age from the growth curve reported by Beintema & Visser
(1989b). No indices were calculated for chicks < 3 days old as the
curve underestimates mass at these ages. Condition was compared
between AES and control sites in a linear mixed model including chick
and site pair as random variables, and chick age and management
as fixed variables. In a second model with chick and site as random
variables, we tested for associations between condition and the area
of late-mown grassland.
Results
Fig. 1. Availability (% of area) of ‘chick grass’ (see Methods) in the
experimental AES sites (closed dots, bold line) and in control sites
(open squares, thin line). Symbols denote actual values, lines
treatment averages.
land, versus 5% in the control. Secondly, field use in two control
sites was relatively low-intensity, although still within the
range of modern farmland. Most important, in all three study
years, rainfall forced farmers to postpone mowing to mid- or
late May in both experimental and control sites.
GODWIT REPRODUCTION
AGRICULTURAL FIELD USE
The area of uncut grass and ‘chick grass’ declined with date in
both experimental and control sites (Fig. 1). The availability
of these field types during the main fledging period did not
differ between AES sites and controls (uncut 29 ± SE 4%
vs. 25 ± 5%, F1,5 = 1·01, P = 0·36; ‘chick grass’ 37 ± 4% vs.
33 ± 4%, F1,5 = 0·74, P = 0·43), and neither did the date on
which it fell below 50% (19 vs. 18 May, F1,5 = 0·11, P = 0·75).
The lack of a treatment effect on habitat availability was not
caused by farmers ignoring AES prescriptions. Mosaic
management was somewhat ‘diluted’ by fields owned by
non-participants and by one AES site including 18% arable
Clutch survival (≥ 1 egg hatched) ranged between 14% and
87% and was higher in experimental sites than in controls
(Table 2). The difference was caused primarily by larger
agricultural losses (to mowing and trampling) in control sites.
Predation probability did not differ between treatments. The
variation in clutch survival among sites was unrelated to the
proportion of grassland not yet cut or grazed in the chick
period (linear regression, F1,10 = 0·05, P = 0·82), possibly due
to more intensive nest protection by volunteers and farmers in
the AES sites.
The mean number of chicks hatched per successful nest
varied from 2·8 to 3·9, but did not differ between AES sites
and controls (Table 2). The mean number of chicks hatched
Table 2. Reproductive parameters of godwits in AES sites and controls. Differences were tested by analysis of variance on site values weighted
by (1 cv −1), but unweighted means are presented here
Mosaic AES
Controls
Difference
Productivity component
Mean
SE1
Mean
SE1
F2
d.f.3
P4
Clutch survival (U)
Clutch failure, agricultural causes
Clutch failure, predation
Chicks hatched/successful clutch (L)
Chicks hatched/breeding pair
Chick survival to fledging (K)
Chicks fledged/breeding pair (B)
0·50
0·06
0·32
3·39
2·09
0·11
0·28
0·03
0·03
0·08
0·10
0·15
0·02
0·05
0·33
0·29
0·37
3·22
1·37
0·11
0·16
0·03
0·11
0·11
0·10
0·15
0·02
0·05
32·7
6·45
0·58
1·6
13·4
0·07
6·82
1,5
1,5
1,5
1,5
1,5
1,4
1,4
0·002
0·052
0·48
0·26
0·015
0·81
0·059
1
standard error; 2F-statistic, ; 3degrees of freedom; 4two-tailed probability.
© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Applied Ecology, 45, 1067–1075
Improving breeding success of black-tailed godwits 1071
Fig. 2. Survival (±SE) of black-tailed godwit
chicks to fledging in relation to the availability of uncut grassland and ‘chick grass’
during the main chick period (black: experimental sites, grey: controls; we failed to estimate
productivity in one control). Lines fitted by
logistic regression. (a) uncut grassland (logit
S = 0·05 × −3·93, F1,9 = 4·58, P = 0·061); (b)
‘chick grass’ (logit S = 0·07 × −5·05, F1,9 =
6·91, P = 0·027).
Fig. 3. Productivity (young fledged /breeding
pair ± SE) of black-tailed godwits in 11 study
sites (black, experimental; grey, controls) in
relation to the availability of uncut grassland
(F1,9 = 1·48, P = 0·26) and ‘chick grass’ (F1,9 =
2·02, P = 0·19) during the main chick period.
The grey bar indicates productivity required
for a stable population. In one site pair we
estimated productivity in 2 years but grassland
use was not quantified in the first year; the
first year estimates (not shown) were 0·20 ±
0·16 for the mosaic and 0·06 ± 0·05 for the
control site.
per breeding pair, integrating clutch survival, probability of
replacing a lost clutch and the number of chicks hatched, was
higher in AES sites than in controls (Table 2). The survival of
chicks to fledging averaged 11% (range 0–23%) and did not
differ between AES and control sites (Table 2). However,
chick survival was positively correlated with the availability of
uncut fields and ‘chick-grass’ during the main fledging period
(Fig. 2).
The number of young fledged per breeding pair was almost
twice as high under mosaic management as in the control sites
(0·28 vs. 0·16; Table 2). In contrast to chick survival, breeding
productivity was not significantly correlated with the
availability of tall grassland in the fledging period (Fig. 3),
mainly because hatching success varied independently.
Breeding output exceeded 0·6 young per pair, required to
balance mortality, in only one out of seven estimates in AES
sites. It was < 0·4 young per pair in all control sites (Fig. 3).
Of 205 chicks of which the radio signal was lost before
fledging, 22% were never recovered, 11% were found dead by
unknown causes, 52% were eaten by predators, 7% were killed
during grass harvesting, and 8% died in other ways. The pro2
portions did not differ among treatments (χ2 test, χ 4 = 6⋅50,
P = 0·16). Given that most ‘missing’ chicks must have died
(indicated by their tagged parents’ behaviour) and may have
been transported out of the search range by predators, ‘predation’ accounted for more than half and up to 80% of chick
losses. However, we could not usually distinguish whether
chicks had been taken alive or found dead by a predator. Birds
(seven species) were identified as chick predators more often
than mammals (four species); common buzzard Buteo buteo
Linnaeus (≥ 9%) and stoat Mustela erminea Linnaeus (≥ 8%)
were identified most frequently.
The average condition index of chicks in 2004 and 2005 was
0·85 (SE = 0·01, N = 175 measurements on 110 chicks); hence,
growth rates were lower than reported by Beintema & Visser
(1989b). Effects of age and management treatment were not
significant (Wald tests: age W1 = 2·50, P = 0·11; management
3·43, P = 0·06), and chick condition was unrelated to the
availability of uncut fields during the fledging period (W1 =
0·00, P = 0·94).
Discussion
Our study adds significantly to the scant data on black-tailed
godwit productivity in The Netherlands. The available
estimates were obtained with different methods and in
different sites with varying management and therefore do not
constitute a true monitoring series, but taken together, they
indicate that breeding success has declined in the past 20 years
(Fig. 4). Although predation has led to very low hatching
success in several sites in recent years, clutch survival seems to
have declined less generally than chick survival. Due to clutch
replacement, it also has a smaller effect on breeding output.
There is little indication that adult survival has declined
structurally (Fig. 4), suggesting that reduced chick survival
has been the main driver of the population decline.
EFFECTIVENESS OF MOSAIC MANAGEMENT
Godwit breeding productivity was 75% higher in AES sites than
in the paired controls. This difference was barely significant
in a two-tailed test but from a knowledge of farming practice
and godwit biology, a higher breeding output was expected
in AES sites and use of a one-sided test can therefore be
© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Applied Ecology, 45, 1067–1075
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H. Schekkerman, W. Teunissen & E. Oosterveld
Fig. 4. Changes in population parameters of black-tailed godwits in The Netherlands. (a) Population indices derived from the SOVON/CBS
meadow bird monitoring scheme (dots connected by line), and available estimates of adult survival (䉫 ring-recoveries, (Beintema & Drost 1986);
䉬 mark-resighting, (Groen & Hemerik 2002; Roodbergen, Klok & Schekkerman in press). (b–d) total breeding productivity (b), and chick (c) and
clutch survival (d) for the studies in (b). Symbols denote different studies: 䊏 (Groen & Hemerik 2002), colour-marked adults; 䊐 (Kruk,
Noordervliet & ter Keurs 1997), colour-marked adults; 䉬 (Schekkerman & Müskens 2000), radio-tagged adults; 䊉 this study; 䊊 (Teunissen,
Schekkerman & Willems 2005), radio-tagged chicks 䉭 Teunissen unpublished, radio-tagged adults. The linear trend over time is negative for
population index (F1,20 = 113·7, P < 0·001), total breeding success (F1,35 = 23·7, P < 0·001) and chick survival (F1,35 = 29·0, P < 0·001), but not for
survival of clutches (F1,35 = 1·43, P = 0·24) and adults (F1,4 = 1·69, P = 0·26).
defended. A weakness in this study was that sites were not
selected randomly but used criteria including a positive
attitude of farmers towards conservation. This may have
led to bias towards a positive ‘meadowbird history’. As a
consequence, higher godwit densities may have accumulated
in AES sites through local production or immigration.
However, reproductive success is sensitive to actual conditions
during the breeding period, and much less likely than breeding
density to reflect historical instead of current management.
We therefore consider our results indicative of a positive effect
of mosaic management on godwit productivity.
The higher breeding success in AES sites arose almost
entirely through a higher survival of clutches, due to lower
agricultural nest losses. The greater intensity of nest protection
in the AES sites than in controls probably contributed to this.
Nest protection is carried out on c. 30% of the agricultural
grassland area in The Netherlands (van Paassen 2006), but its
nearly complete coverage in the AES sites was part of the
management prescriptions. Previous studies from The Netherlands have shown that differences in meadowbird breeding
density between fields managed under AES and controls can
be accounted for by differences in groundwater levels rather
than any effect of management itself (Kleijn & van Zuijlen
2004; Verhulst, Kleijn & Berendse 2007). However, the higher
nest survival found here is unlikely to be related to environmental factors that happen to correlate with fields selected for
AES management.
Although mosaic management explicitly aims to increase
chick survival, this did not differ between AES sites and
controls. A primary objective – making available more ‘chick
grass’ than in conventionally farmed sites – was not achieved.
Rainfall forced farmers to postpone mowing in both AES and
control sites, and led to a very similar timing of the first cut. It
also led to a less spatially diverse grassland use than intended,
as cutting was no longer staggered with weekly intervals
but proceeded rapidly on fields scheduled for mowing in
May when weather improved. Nevertheless, chick survival was
positively correlated with the availability of tall grass among
sites, irrespective of their treatment status, indicating that
mowing later is beneficial to chicks. It suggests that in years
with drier May weather, resulting in earlier mowing on conventional farms, better chick survival will add to the higher
productivity in AES sites. However, our results do show that
AES management overlaps with between-year variation in
conventional farmland use, and will therefore not deliver
value for money in all years, unless prescriptions ensure
that mowing is still spread in time and space after an initial
postponement.
© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Applied Ecology, 45, 1067–1075
Improving breeding success of black-tailed godwits 1073
Average productivity of black-tailed godwits in AES sites
(0·28 fledged young pair−1) was clearly below the c. 0·6
required for reproduction to balance mortality. This criterion
is based on estimates of 60% first-year post-fledging survival,
85% adult annual survival, and first breeding at 2 years
(Beintema & Drost 1986; Groen & Hemerik 2002). Its
magnitude depends particularly on adult survival, which
should be as high as 92% for the observed productivity to be
sufficient. Annual survival of colour-marked adult godwits in
two of our study sites in 2003–2005 was 81% (95% CI, 73–
87%; Roodbergen, Klok & Schekkerman in press). It is therefore improbable that mean adult survival in AES sites reached
92% and we conclude that the observed breeding productivity
was insufficient to sustain the population.
Our productivity estimates assume that black-tailed
godwits re-lay only once after clutch loss (which is generally
the case), and that replacements yield as many fledglings as first
clutches. While we did not find a decrease in chick survival
with date (own unpublished data), clutch survival may decline
later in the season (Beintema & Müskens 1987). As more
clutches were lost in the control sites, productivity would be
reduced further here and the differences between treatments
would be more pronounced, but it would not affect our conclusion that productivity in AES sites was insufficient. Hence,
godwit populations under mosaic management still depend
on immigration for their long-term persistence. As our results
show that even fewer young fledge in conventional farmland,
the necessary recruits should come from meadowbird reserves,
but there are too few data to evaluate whether breeding
success is sufficient there.
MECHANISMS REDUCING CHICK SURVIVAL IN
FARMLAND
Several factors probably contribute to the observed decline in
chick survival. The correlation between fledging success and
availability of uncut grassland points to the importance of the
mowing regime. Earlier and faster mowing means that an
increasing proportion of chicks will encounter machinery
and will be faced with large expanses of homogeneous short
swards offering little food and cover.
Deaths by cutting and harvesting made up at least 7% of
chick losses in our study, but may have been underestimated.
Some chicks may have been scavenged from recently cut
fields, and some transmitters may have been destroyed by
machinery or buried in silage stacks. Some broods escape
mowing (Kruk, Noordervliet & ter Keurs 1997) by moving to
nearby uncut fields but these are equally dangerous when
fields are cut in rapid succession. Cutting grassland later and
spread in time and space will thus reduce mortality.
A detailed analysis of chick mortality in the current study
sites and three other sites found that predation was twice as
high when broods stayed in recently cut or grazed fields compared to uncut fields (Schekkerman, Teunissen & Oosterveld
in press). Short swards evidently render chicks vulnerable to
(avian) predators. Hence, a scarcity of uncut grassland that
forces broods to use cut fields will increase predation losses.
Invertebrates are less abundant in cut than in uncut
grassland, leading to a reduction in foraging success of chicks
to a degree large enough to compromise their growth
(Schekkerman & Beintema 2007). Although chicks grew more
slowly in our study than those observed by Beintema & Visser
(1989b) in 1976–1985, we did not find a correlation between
chick condition and the availability of tall grass, and only 2%
of the recovered chicks evidently starved to death (uninjured,
condition index c. 0·5). However, chicks with a deteriorating
condition may be quickly eliminated by predators (Swennen
1989; Schekkerman, Teunissen & Oosterveld in press).
Earlier mowing dates may not explain the observed decline
in chick survival completely. In agreement with our study,
Schekkerman & Müskens (2000) found that chick survival
increased with the area of grassland mown late in nine
farmland sites in 1997–2000, yet average survival was notably
higher than in the current study (mean 26%, Fig. 4) despite a
smaller proportion of fields being mown late (11 ± 2% cut
after 31 May vs. 21 ± 6% in the current study). This suggests
that additional factors are involved.
Between 1990 and 2005, an average 8% of all grasslands in the
north and west Netherlands were reseeded annually (Statistics
Netherlands), leading to a strong increase in productive grass
monocultures at the expense of herb-rich fields. This is likely
to have reduced arthropod abundance and diversity (Vickery
et al. 2001; Atkinson et al. 2006; Schekkerman & Beintema
2007), and impaired the chicks’ ability to move and capture
prey in the resulting dense vegetation (Butler & Gillings
2004; Wilson, Whittingham & Bradbury 2005). The quality
of grassland as chick foraging habitat may thus have declined
independent of cutting dates.
Poor condition and survival may also result from unfavourable weather (Beintema & Visser 1989a; Schekkerman &
Visser 2001). Linear trends over 1976–2005 (data from the
Royal Netherlands Meteorological Institute) suggest a slight
increase in mean daily maximum temperature (from 16·1 to
17·3 °C), no change in wind speed and an increase in rainfall
duration (from 4 to 6% of time), but these changes were not
significant due to interannual variability (linear regression,
P = 0·15– 0·34). As warmer weather and increasing rainfall
will have opposite effects on chicks, it is unclear how climate
variation has affected conditions for growth.
Our finding that 50–80% of non-surviving chicks were
taken by predators, frequently common buzzard, suggests
that predation pressure may have increased. Since the late
1970s, buzzards have (re)colonized the entire Dutch ‘meadowbird landscape’ (SOVON 2002), and other raptors have
followed. Simultaneously, intensive farming practices have
rendered godwit chicks vulnerable to predators by reducing
the availability of cover and the density of nesting birds that
can cooperate to evict predators (Green, Hirons & Kirby 1990).
The observed frequency of ‘predation’ could overestimate
its importance if it included much scavenging or concerned
mainly chicks with reduced survival prospects due to other
factors. The telemetry data suggest that scavenging was not
very common, but we did observe that chicks in poor condition
were more prone to disappear. However, the high predation
© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Applied Ecology, 45, 1067–1075
1074
H. Schekkerman, W. Teunissen & E. Oosterveld
losses are only partly explained by such interaction effects
(Schekkerman, Teunissen & Oosterveld in press).
MANAGEMENT RECOMMENDATIONS
Godwit chick survival has been reduced in recent decades by
progressively earlier mowing dates, which has increased
mowing mortality, reduced food availability, and increased
the vulnerability of chicks to predators. At the same time, the
quality of uncut grasslands as foraging habitat has deteriorated
and important predators have increased. These changes mean
that more stringent conservation measures are necessary now
than a few decades ago to raise breeding productivity to a
level that can sustain the population. Breeding output was
higher under mosaic management than in control sites, but
chick survival needs to be more than doubled to achieve longterm sustainability. Many other grassland birds face similar
problems (Donald, Green & Heath 2001, Teunissen & Soldaat
2006).
Their low productivity indicates that prospects are bleak
for maintaining black-tailed godwit populations in farmland
if no effective conservation measures are put in place. Our
results indicate that both the proportion of grassland mown
late and its quality as chick habitat must be improved substantially. AES prescriptions do not include specifications on
fertilizer input or floral composition of fields contracted for
late mowing. Including such entry criteria would promote an
open vegetation structure with abundant insects. However,
these criteria would decrease the flexibility in field use that
currently makes the AES attractive to farmers. On balance,
fewer sites with more specific prescriptions will yield greater
conservation benefit to black-tailed godwit than widespread
efforts that are not effective in the long-term. Concentrating
conservation efforts in godwit strongholds will be more
feasible and will facilitate optimization – by choice of location
or by management – of environmental conditions including
landscape structure, water levels, disturbance and predation
pressure.
Acknowledgements
The mosaic management AES was initiated by Birdlife Netherlands, Landschapsbeheer Nederland and Natuurlijk Platteland Nederland, and supported
by the Postcode Loterij. These NGOs and the Dutch Ministry of Agriculture,
Nature Management and Food Quality commissioned the research described
here. Many people, particularly farmers and volunteers in the study areas,
assisted by providing access to land, finding and monitoring nests and other
means. Much fieldwork was done by students and field staff. L. Beskers,
K. Bouwman, I. Geelen, P. Heemskerk, Y. van der Heide, B. Henstra, H. de Jong,
A. van Kleunen, M. Kuiper, F. Majoor, G. Müskens, W. Nell, K-P. Plas,
T. Meijer, E. Vromans, F. Weijdema and F. Willems. F. Berendse, G. Gerritsen,
H. Krüse, T. Piersma and G. de Snoo suggested improvements to this study.
R.H. Drent and T. Piersma commented on drafts of this paper.
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Received 27 July 2007; accepted 13 May 2008
Handling Editor: Mark Whittingham
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