Changes in closed avian population sizes are deter-
mined by survival and reproduction rates (Nichols
1991). Measures of both are often desired by wildlife
conservationists, particularly when changes in stock
size are difficult to observe directly (Caughley 1977,
Eichholz & Sedinger 2007). They may also be used as
baseline figures in environmental impact studies that
aim at predicting losses in wildlife populations through
anthropogenic causes (Morrison et al. 1998, Dierschke
et al. 2003, Sperduto et al. 2003). In birds, survival can
be measured either from live recaptures of marked indi-
viduals or from ring recoveries of birds recorded as
dead (Clobert & Lebreton 1991). A powerful methodol-
ogy has been developed for the analysis of such data
obtained under various conditions (White & Burnham
1999). Grebes Podicipedidae, however, are difficult to
catch, which makes live recapture programs impractica-
ble, and grebe ring returns are very scarce. Attempts to
estimate survival have been made for the Great Crested
Grebe Podiceps cristatus (Fuchs 1982, van der Poel
1984), but these were based on small sample sizes.
Aiming to estimate survival rates for Great Crested
Podiceps cristatus, Black-necked P. nigricollis, and Little
Grebe Tachybaptus ruficollis, we collected ring recovery
records from many parts of Europe compiled over a
period of 57 years.
Survival rates of adult European grebes (Podicipedidae)
Abt K. & Konter A. 2009. Survival rates of adult European grebes (Podicipe-
didae). Ardea 97(3): 313–321.
Ring recoveries of dead individuals from all over Europe and covering a period
of 57 years were collected to study survival of Great Crested Podiceps cristatus
(n = 433), Black-necked P. nigricollis (n = 95) and Little Grebes Tachybaptus
ruficollis (n = 295). Survival rates of adult birds were estimated by fitting simple
mark–recapture models via maximum-likelihood. Realizing that the samples
were extremely heterogeneous and possibly biased, it was further investigated
how the survival data conformed to information from literature on fledging suc-
cess, age at first breeding, and long-term population trends. In the Great
Crested Grebe, ring recoveries were biased towards young birds, as indicated
by a marked, untypical increase in apparent survival after the age of 3 years.
Also, the whole-sample estimate of 0.66 was too low to match the other demo-
graphic parameters. The survival rate of 0.75 (95% CI 0.69–0.80) estimated for
birds of 4 years and older conformed well with the breeding performance estab-
lished for Great Crested Grebes and is thus considered as a realistic estimate
for adult birds. The survival rate estimate of 0.63 (95% CI 0.55–0.70) for the
Black-necked Grebe seemed a slight underestimate given estimates for the
other demographic parameters. Apart from a possible, albeit undetected, sam-
ple bias towards younger birds, some influence of ring loss cannot be excluded,
because in contrast to the other two species, the Black-necked Grebe sample
contained a high proportion of aluminium rings. The survival rate of Little Grebe
was estimated at 0.60 (95% CI: 0.55–0.64), which corresponded well with other
Key words: population dynamics, survival, ring recoveries, mark–recapture,
Podiceps cristatus, Podiceps nigricollis, Tachybaptus ruficollis
1Wildlife Consulting, Samwerstr. 32, 24118 Kiel, Germany;
245, rue des Romains L-6478 Echternach; collaborator of the Museum of
Natural History, Luxembourg, L-2345 Luxembourg;
*corresponding author (email@example.com)
Kai Abt1& André Konter2,*
The heterogeneous nature of the ring recoveries,
and potential bias therein, may complicate their inter-
pretation (e.g. Botkin & Miller 1974, Fuchs 1982). To
check the accuracy of the survival estimates, we con-
structed a simple population model that included inde-
pendent information on fledging success, age at first
breeding, and long-term population trends as derived
Inference from ring recoveries
Upon request, we received records on ringing and
recoveries for all five European grebe species from 25
ringing centres throughout Europe (see Acknowledge-
ments). Samples of Red-necked P. grisegena, and
Horned Grebes P. auritus were too small for analysis. To
estimate survival rates we only used dead recoveries,
which formed the majority of the records. Live-recap-
ture data from local ringing programs were screened for
birds of old age. Among dead recoveries, 45% of Great
Crested Grebes and 39% of Little Grebes appeared to be
victims of an anthropogenic source, mainly by drown-
ing in fishing nets and hunting (Table 1). However, in
about half of the cases no cause of death had been
reported, and it is likely that many of these had died by
anthropogenic causes as rings of birds starved or killed
by predators must have a low chance of recovery. A pri-
ori, this needs not be a problem, provided that birds of
every age and sub-population are equally affected by
anthropogenic mortality agents. In reality, however, it is
necessary to consider that samples obtained in this way
may be significantly biased.
We analysed ring recovery data of birds that had
survived at least their first winter, i.e. birds found dead
from 1 May of their second calendar year on and that
had been reported to be dead for no longer than a few
weeks. In a few instances, no remains of the bird were
found together with the ring. The corresponding data
were not included in the analysis because of a possibly
long time lag between death of the bird and ring recov-
ery. We defined year of death k from 1 May of calendar
year k to 30 April of calendar year k + 1. Age at death
was then given by year of death minus presumed year
of hatching. The latter in turn was inferred from age at
ringing, as known from EURING age codes (Speek et al.
2001) indicated by the ringers (Table 2). Because infor-
mation from codes 0, 2, 4, and 6 is not precise, we
made the following assumptions: birds with code 0 and
2 were regarded to be in their second calendar year
when ringed before the month of peak occurrence of
pulli, i.e. July in Great Crested and June in Little Grebe.
When ringed in or after that month, however, they
were regarded as fledglings of the year. Birds with code
4 were treated as if they had been ringed in their sec-
ond calendar year. To simplify modelling, this was also
done with the very few birds with code 6, that theoreti-
cally could be classified as being at least in their third
calendar year. As the year of hatching was not defi-
nitely known in 58% of the birds, we suspect that ‘age’
referred to in the following is an underestimation of the
From the obtained frequencies of deaths at different
‘ages’, the survival rates from the second calendar year
ARDEA 97(3), 2009
Great Crested Black-necked Little Grebe
(n = 433)(n = 95)
(n = 295)
Dead, unknown cause
Drowned in fishing net
Table 1. Reported causes of death of dead recovered grebes (as
% of total numbers).
Great Crested Black-necked
(n = 433)
(n = 295)
(n = 95)
0 Age unknown
or not indicated
1 Pullus, unable to fly
2 Fully grown bird,
able to fly
3 Fully grown bird,
hatched in this
4 Fully grown bird,
hatched before this
5 Fully grown bird in the 2.5
second calendar year
6 Fully grown bird in the 3.0
third calendar year
Table 2. EURING age code and distribution of dead recovered
grebes (as % of total numbers).
Abt & Konter: SURVIVAL OF GREBES
on was estimated using methodology outlined by White
& Burnham (1999). We employed a simple, holistic
ring recovery model that omits the (unknown) cohort
sizes of birds ringed and assumes adult survival to be
constant with age, year, and location. The probability
that a bird is found dead in a particular year can be
Pxy= S x – 1(1 – S) (1 – S y) –1,
where S is survival rate, x = 1, 2, 3, … is ‘age’ at death,
and y = 1, 2, 3, … is the number of years at risk, i.e.
the last year of the sampling period (2000 in Great
Crested, 2002 in Black-necked, 1998 in Little Grebe)
minus assumed year of hatching. The term S ydenotes
the probability that a bird hatched in year y–1 (and
thus one year old in year y) is still alive after the last
year of the sampling period. It approximates zero as y
becomes larger. The parameter S was determined by
maximum-likelihood estimation, i.e. by fitting S such as
to maximize the log-likelihood term
Log L = ∑ NxyLog Pxy,
where Nxyis the number of grebes ringed in year y and
found in year x. Confidence limits of S were found by
the curvature method, as described in Schrago (2006),
based on angular-transformed values.
In addition to the above model, which assumes con-
stant survival throughout all age-classes, we employed
a design allowing for a change in survival rate at a
given age, i.e. models with two age groups. This was
done in order to detect possible heterogeneity in the
data that might lead to biased results from the model
without age groups. The age groups distinguished var-
ied from 2 until the highest figure for which at least 20
birds were left in the older group. Model selection was
based on Akaikes’s information criterion (AIC), a func-
tion of the likelihood and the number of model param-
eters. Based on the parsimony principle, a lower AIC
value indicates better model fit at limited complexity
(Burnham & Anderson 1998). AIC differences of >2
were considered noteworthy.
Inference from fledging rates
Establishing survival from fledging rates requires
knowledge of approximate population trends. Euro-
pean Great Crested Grebes mainly increased during the
second half of the 20th century, with data from The
Netherlands, UK, France, Belgium, Estonia, Norway
and Fennoscandia suggesting an average growth rate of
4–5% per year over at least 3–4 decades (Bauer &
Berthold 1996, O’Donnell & Fjeldså 1997, Snow &
Perrins 1998, BirdLife International 2000, 2004, Bauer
et al. 2005). There was a moderate decline in Western
Europe during the 1990s (BirdLife International 2004,
Bauer et al. 2005), which is, however, of minor impor-
tance because less than 7% of the ring recoveries for
this species were from that decade. Population data for
the Black-necked Grebe are less conclusive, although
they similarly indicate an increase between 1960 and
1990 in Western and Central Europe, and, after 1990,
local declines in some Eastern European countries
(Bauer & Berthold 1996, O’Donnell & Fjeldså 1997,
BirdLife International 2000, 2004). Little Grebe num-
bers remained stable, although undergoing consider-
able short-term fluctuations which relate to occasional
high winter mortality (O’Donnell & Fjeldså 1997,
BirdLife International 2004, Bauer et al. 2005). In our
models, we assumed a stable population of the Little
Grebe over the study period, which means that the
finite rate of increase (λ) equals 1.00. For the other two
species we considered both a stable stock and one that
increases at 5% per year (λ = 1.05).
Information on the annual number of fledglings per
breeding pair (F) was also obtained from literature.
In the Great Crested Grebe, the broad average appears
to be within 1.0–1.5 fledglings per breeding pair
(Prinzinger 1979, Vlug 1983, Ulfvens 1988, Ulenaers &
Dhondt 1991, Arratíbel et al. 1999, Konter 2004).
Figures of 1.0–2.0 are considered for the Black-necked
Grebe (Bandorf, Fiala, Knötzsch in Prinzinger 1979,
Leibl & Zach 1992). Little Grebes have as many as
2.0–2.5 fledglings per breeding pair due to frequent
second broods (Bandorf 1970, Hughes 1992,
Dittberner 1996). Note that all mature birds are
assumed to be part of the breeding population to which
In order to establish adult survival rate (S), which
we assumed to be constant from age 1 onwards, we
need to know the survival rate of fledglings (S1), since
S + S10.5 F = λ.
Lacking knowledge of both survival rates, S1may be
expressed as a function of S. We assumed that first-year
mortality (1 – S1) is elevated by some factor k in rela-
tion to adult mortality (1 – S), i.e.
(1 – S1) = k (1 – S),
with k supposedly being in the range of 1–2 (see
Discussion). Finally, we took account of delayed breed-
ing, thus the younger age classes may not be part of the
breeding population which literature values of F refer
to. Assuming that birds start breeding at some specific
age f, the annual recruitment is proportional to S f – 1,
rather than to S. Hence, we arrive at
S + S f – 1[1 – k (1 – S)] 0.5 F = λ.
If f assumes low naturals (1, 2) and λ equals 1, this can
be solved for S by linear algebra. Otherwise, S must be
found using Newton iterations.
According to Bandorf (1970) and Fjeldså (2004),
Little Grebes generally breed from their second calen-
dar-year onwards (i.e. f = 1). Great Crested Grebes may
sometimes breed at the age of one year, but usually first
breed at the age of two years (f = 2) (Simmons 1989,
Vlug 1983, 1985, 2007). Black-necked Grebes are sexu-
ally mature in their second calendar-year (Prinzinger
1979), but common occurrence of non-breeders, pre-
sumably second-year birds, near colonies (Konter,
unpubl.) suggest that f = 1.5 may be more adequate for
the European nominate.
As indications of minimum longevity, recorded maxi-
mum ages of grebes are given in Table 3. Obviously, the
Great Crested Grebe can exceed 20 years of age. No
Black-necked Grebe older than 13 years was found,
which must be seen in relation to the small overall
number (37) of recovered birds ringed before 1989. As
the oldest bird was shot, it could have grown older. A
ARDEA 97(3), 2009
Species Ringing schemeAge codeRinging dateRecovery dateAge (years) Circumstances
Great Crested GrebeSpain
Dead for more than 1 week
Black-necked GrebeCzech4 08.06.65 03.08.7713 Freshly shot
Ring found only
Table 3. Recorded maximum ages of grebes from dead and live recaptures; individual numbers of live recaptures were 77 in Great
Crested, 7 in Black-necked, and 131 in Little Grebe. See Table 2 for age codes.
N in older
Survival rate of
younger age group
Great Crested Grebe1+
Black-necked Grebe 1+
Table 4. Results of mark–recapture analysis of grebe dead recoveries; each row contains the results of a different model; the first,
basic model (older age group = 1+) returns a single average survival rate for the entire sample, while the others assume a change of
survival at a given age with survival rates for the two age groups; ∆AIC indicates how well a model explains the data as compared to
the basic model, with negative values denoting better performance.
Abt & Konter: SURVIVAL OF GREBES
Little Grebe was released alive when at least 17 years
old. The oldest record referred to a 23-year old bird, but
as no remains were found this record is questionable.
The basic mark–recapture model yielded average
adult survival rates of 0.66 (95%-CI 0.62–0.69), 0.63
(0.55–0.70), and 0.60 (0.55–0.64) in Great Crested,
Black-necked, and Little Grebe, respectively (Table 4).
In the Great Crested Grebe, however, models allowing
for a change of survival rate with age provided a better
description of the data. Model selection indicated a
strong support for the model with a shift in survival at
age 4. The survival estimate for the older group
increased with the age of splitting until a maximum
value was attained at age 4. Survival of Great Crested
Grebes of at least 4 years of age was estimated at 0.75
(95%-CI: 0.69–0.80). In the other two species, there is
no statistical support for a shift in survival with age.
Adult survival rates inferred from the simple popu-
lation model are given in Table 5. The observed popula-
tion increase of 5% per year (λ = 1.05) in Great
Crested and Black-necked Grebe requires that survival
rates are 0.02–0.03 higher than for a stable population.
Changes in k make little difference when f = 2 and
F ≤ 1.5 as in the case of the Great Crested Grebe. In the
Little Grebe, in contrast, where f = 1 and F = 2.5, k has
a considerable influence on the resulting survival rate.
In the Great Crested Grebe, the survival estimate of
0.66 from the basic mark–recapture model implies
equally high survival during the first year (k = 1.0) and
more than 1.5 fledglings per pair (Table 5). With mod-
erately elevated first-year mortality (1.0 < k < 1.5)
and less than 1.5 fledglings, however, adult survival
must be substantially higher, i.e. at least of the magni-
tude found in birds of 4 years and older (0.75), to
maintain a stable or increasing population. In the
Black-necked Grebe, similarly, the mark–recapture esti-
mate of 0.63 requires either equally high first-year sur-
vival and about 1.5 fledglings per pair, or as many as 2
fledglings with moderately lower first-year survival
(1.0 < k < 1.5). The situation in the Little Grebe is
exceptional in that F is relatively well-known, and S is
particularly sensitive to changes in k. The survival rate
estimate of 0.60 conforms to a moderately elevated
first-year mortality (k ~ 1.5), while F may be 2.0–2.5
fledglings per pair.
The goal of this investigation was to establish average
survival rates of European grebes in the second half of
the 20th century. Compared to other mark–recapture
studies, we pooled records collected over a very long
sampling period and from a large area. This was neces-
sary to obtain reasonable sample sizes, given the lim-
ited number of ring recoveries in each grebe species.
Also, the samples are clearly biased towards certain
countries (particularly The Netherlands and Switzer-
land), but as long-term population trends in grebes
seem to have been similar over large parts of the
Species Age at first
per pair (F)
of increase (λ)
Adult survival rate at ratio (k)
of first-year vs. annual adult mortality
k = 1.0k = 1.5k = 2.0
Great Crested Grebe2 1.01.05
Black-necked Grebe1.5 1.01.05
Table 5. Annual survival rates of adult grebes calculated from age at first breeding (f), fledging rates (F), population rates of increase
(λ), and ratio between first-year and annual adult mortality (k).
species’ range (O’Donnell & Fjeldså 1997, BirdLife
International 2004, Bauer et al. 2005), the results may
be applicable to much of the European range.
Because our ring recoveries originate mainly from
anthropogenic mortality, certain bias in the samples
was to be expected. In particular, younger birds may be
overrepresented relative to older, more experienced
individuals. Apparent consequences thereof are dis-
cussed farther below. Another possible source of bias is
ring loss (Botkin & Miller 1974, Nelson et al. 1980). For
North American Eared Grebes P. nigricollis californicus
staging at the highly saline Mono Lake, California, alu-
minium ring loss begins within 3–4 years and becomes
a serious problem within 5–6 years from ringing (Jehl
1990). This is of particular relevance in the Black-
necked Grebe, because in this species most rings recov-
ered were from Eastern European schemes, which used
aluminium rings until recently. In contrast, the UK, The
Netherlands and Switzerland introduced stainless steel
rings in the 1960s, followed by Finland and Germany
between 1968 and the early 1980s (J. Clark, M. Kesten-
holz, J. Haapala, W. Foken, W. Fiedler, R. Wassenaar,
S. Kharitonov, J. Cepák, pers. comm.). Therefore, about
half of our Great Crested and Little Grebe samples con-
sist of steel rings, giving little reason for concern about
substantial influence of ring loss in our results.
Moreover, significant ring loss typically leads to an
apparent decrease of survival with age (Nelson et al.
1980), a pattern not observed in our analysis of ring
As to the indirect assessment of survival rates, infer-
ence from fledging success may give rise to biased
results as well. For instance, Vlug’s (1983) average fam-
ily size of 1.1 for Great Crested Grebes, based on 19
561 breeding pairs from various European populations,
includes chicks of various age classes. This may have
overestimated fledging success. On the other hand, the
figure does not account for second and third broods. As
a consequence, it may even represent a conservative
estimate of fledging success. Furthermore, published
fledging rates may not be representative for the entire
period from which ring recoveries were obtained.
However, recalling that populations remained broadly
stable (Little Grebe) or increased for most of the sam-
pling period (Great Crested Grebe), significant change
of population parameters may not be inferred. As we
considered a range of F-values, possible changes of pro-
ductivity are unlikely to be an important source of error
in the calculations. Among the parameters considered,
the least-known was first-year mortality, which we
introduced in the form of the artificial parameter k.
Assuming some specific ratio of first-year vs. adult
annual mortality has no theoretical justification, but it
makes some sense from an empirical point of view. For
the Great Crested Grebe, Fuchs (1982) estimated 41%
first-year and 30% adult mortality in a decreasing pop-
ulation in Switzerland, yielding a k-value of 1.37. In
divers Gavia spp., which ecologically are to some extent
comparable to grebes, but have fewer offspring (F ~
0.55) and presumably higher adult survival (S ~ 0.88;
Sperduto et al. 2003), k equals about 2. Higher values
of k seem unlikely for grebes because they imply either
very high adult survival rates, like in loons and many
seabirds, or higher offspring numbers than those
observed. Some small- to medium-sized raptors, i.e.
Sparrowhawk Accipiter nisus, Goshawk Accipiter gentilis,
and Peregrine Falco peregrinus, have k-values between
1.5 and 2.0, while, roughly comparable to grebes, adult
survival rates are in the range of 0.65–0.80, and fledg-
ing rates (including unsuccessful pairs) within 1.5–3.0
(Newton & Rothery 1998, Snow & Perrins 1998, Nielsen
& Drachmann 2003, Robinson 2005).
In the Great Crested Grebe, ring recoveries indi-
cated a substantially lower survival rate of 1–3-year-old
individuals (0.62), as compared to birds of 4 years and
older (0.75). For three reasons, this is almost certainly
an artefact, resulting from overrepresentation of young
birds in the samples. First, low juvenile survival (0.62
vs. 0.75 in ‘adults’) is very unlikely to extend until age 3
in a species that starts to breed at age 2. In general, a
major change of survival after the first year of life is
untypical in birds (Caughley 1977). Second, the aver-
age figure of 0.66 obtained from the entire sample is
too low to allow for a most likely elevated mortality
during the first year (Melde 1973, Fuchs 1982, van der
Poel 1984). Finally, it implies an average fledging rate
of more than 1.5, which compares poorly to Vlug’s
(1983) mean family size of 1.1. Even if the latter was a
slight underestimate, because it disregards multiple
broods, the survival rate estimate obtained from the
birds older than 4 years seems more realistic. Therefore,
we consider a survival rate of 0.75 as a plausible value
for adult Great Crested Grebes.
In the Black-necked Grebe, in contrast, there is no
indication of a significant change of survival at an
unusual age. However, this does not necessarily imply a
representative sample, but it could be due to the rela-
tively small number of records. At least, our estimate of
0.63 is in line with the literature, as Sperduto et al.
(2003), summarizing a number of references, quote a
similar value of 0.62 for adult North American Horned
and Red-necked Grebes. However, these authors also
assume high productivity (f = 1, F = 1.82) and a high
fledgling survival (0.60). For the European Black-
ARDEA 97(3), 2009
Abt & Konter: SURVIVAL OF GREBES
necked Grebe, data on fledging success are relatively
scarce, but there is little support for an average as high
as 1.5–2.0 (Prinzinger 1979, Leibl & Zach 1992).
Moreover, a lack of higher mortality during the first
year seems counterintuitive, considering the evidence
in both the Great Crested and the Little Grebe (see
below), and many other European bird species (Snow
& Perrins 1998, Robinson 2005). Therefore, the sur-
vival rate of adult Black-necked Grebes in stable or
increasing populations may rather be close to 0.70, or
even higher. Ring loss and bias towards young birds,
both undetected due to the limited statistical power of
the sample, are possible reasons why our estimate is
lower. In any case, uncertainty about population
parameters remains high in this species, which could
partly be a consequence of high variability in time, as
suggested from fluctuations in population size
(O’Donnell & Fjeldså 1997). For North American Eared
Grebes, Jehl et al. (2002), referring to Cullen et al.
(1999), suggest a survival rate as high as 0.95 in both
adults and fledglings between 1998 and 2000.
However, this figure refers to a two-year period in
which the grebe population doubled, recovering from a
catastrophic decline related to an El Niño event. The
long-term average survival rate, including periods of
decline, will be lower. Assuming that population num-
bers fluctuate around some stable mean, and accepting
values of further vital parameters as suggested by the
authors (f = 1, F = 0.8, k = 1), the average survival
rate of the North American sub-species would in fact be
down to 0.71.
In the Little Grebe, there is also no indication of bias
in the mark–recapture sample. Given the high produc-
tivity of the species, our survival rate estimate of 0.60,
corresponding to a k-value of about 1.5, is realistic. As
in the Black-necked Grebe, the result summarizes both
population crashes and recovery periods, and should
thus represent the long-term mean survival rate.
Referring to the large short-term fluctuations, Vlug
(2005, 2007) postulated low survival of Little Grebes
and suggested a key role of suitable winter habitat.
From the fact that both juveniles and adults face at
least occasional high winter mortality, one may expect
that the survival rates of both age groups do not differ
too much, and, thus, k tends to be lower than in other
grebes. From our results, however, figures lower than
1.5 seem unlikely even for the Little Grebe. As there
also is little support for k ranging much higher in any of
the species, values around 1.5 may be generally ade-
quate for European grebes.
Looking at adult survival rates of other non-pelagic
water birds, we find that many estimates are in the
range of 0.60–0.75 suggested here for European grebes,
e.g. 0.61–0.75 for Gadwall Anas strepera (Giudice
2003, Szymczak & Rexstad 1991), 0.66 for Hooded
Merganser Lophodytes cucullatus, 0.63 for Wood Duck
Aix sponsa (Dugger et al. 1999), 0.65 for Common
Pochard Aythya ferina, and 0.71 for Tufted Duck Aythya
fuligula (Blums et al. 1996). Of course, anatids have
more offspring than grebes, implying that fledgling sur-
vival will be lower.
Obviously, animal survival rate estimates are easily
under-estimated for a number of reasons. As we have
shown, however, severely biased results can be identi-
fied if information on reproduction and population
trends of the species is utilized. We believe that wildlife
population research could benefit from a more common
use of this approach, in a way that obtained estimates
be discussed more critically to avoid unrealistic values.
For instance, Sperduto et al. (2003) list first-year and
adult survival rate, fledging rate, and age of first breed-
ing from various references for seven taxa of marine
birds, and use these figures to estimate population
losses from the ‘North Cape’ oil spill off Rhode Island in
1996. Employing the population model above reveals
that the parameters assumed by the authors for Red-
breasted Merganser Mergus serrator, Common Golden-
eye Bucephala clangula and Common Eider Somateria
mollissima would lead to quasi-extinction (i.e. a 90%
population loss) within 9–11 years. As no such dra-
matic declines have been reported, either fledging or,
more likely, survival rates must be too low. We believe it
may be useful in studies of animal survival to perform
some test of plausibility, based on information on stock
trends and reproduction. Moreover, as the latter param-
eters are often easier to establish, indirect estimation of
survival rates by means of simple population models
may be the best solution, particularly if direct estimates
from marked animals are missing or appear unreliable.
We are indebted to the following ringing schemes that have con-
tributed with their data to this study: Belarus Ringing Centre,
Minsk; Beringungszentrale Hiddensee, Stralsund; Bird Ringing
Centre, Moscow; Bird Ringing Centre, Prague; Bird Ringing
Centre Swedish Museum of Natural History, Stockholm; British
Trust for Ornithology, Thetford; BSPSM, Skopje; Centre for
Animal Marking, Belgrade; Copenhagen Bird Ringing Centre,
Copenhagen; CRBPO Muséum National d’Histoire Naturelle,
Paris; EURING, Heteren; Hellenic Bird Ringing Centre, Athens;
Hrvatska Akademia Zmanosti Umjetnosti, Zagreb; Icelandic Bird
Ringing Scheme, Reykjavik; Lithuanian Bird Ringing Centre,
Kaunas; Matsalu Bird Ringing Centre, Läänemaa (Estonia);
Oficina de Especies Migratorias, Madrid; Ornithological Station
ARDEA 97(3), 2009
of the Institute of Ecology, Gdansk; Ringing Centre Finnish
Museum of Natural History, Helsinki; Royal Belgian Institute of
Natural Sciences, Brussels; Schweizerische Vogelwarte,
Sempach; Ukrainian Ringing Centre, Kiev; Vogeltrekstation
Arnhem, Heteren; Vogelwarte Helgoland, Wilhelmshaven;
Vogelwarte Radolfzell, Radolfzell. Many thanks also to the
LNVL, Luxembourg, and to the Museum of Natural History,
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Om de overleving van futen (Podicipedidae) te schatten werden
de ringvondsten uit een groot aantal Europese landen verza-
meld. Voor de Fuut Podiceps cristatus (433 terugmeldingen),
Geoorde Fuut P. nigricollis (95) en de Dodaars Tachybaptus rufi-
collis (295) was het aantal terugmeldingen (verzameld over een
tijdsbestek van 57 jaren) voldoende voor een dergelijke schat-
ting. Om te kijken of de overlevingsschattingen realistisch
waren, werd de overleving ook geschat aan de hand van een
simpel populatiemodel met literatuurgegevens over populatie-
groei, jongenproductie en de leeftijd waarop de vogels met
broeden beginnen. Bij de Fuut bleek de geschatte jaarlijkse over-
leving na het derde levensjaar toe te nemen. Een dergelijke
trend lijkt onwaarschijnlijk en is waarschijnlijk een gevolg van
het feit dat ringvondsten van jonge vogels (om welke reden
ook) oververtegenwoordigd waren. Bovendien leverden de
terugmeldingen een schatting op van een overleving van 0,66.
Dit bleek te laag om de waargenomen groei van de Europese
populatie te verklaren. Een schatting van de overleving op
grond van terugmeldingen van Futen van 4 jaar en ouder (0,75)
bleek goed in overeenstemming te brengen met het populatie-
model. De ringgegevens van de Geoorde Fuut wezen op een
overlevingskans van 0,63. Dit was een lichte onderschatting in
vergelijking met het populatiemodel. Een onderschatting van de
overleving kan veroorzaakt zijn door het feit dat veel van de
Geoorde Futen waren geringd met aluminiumringen, die een
beperktere levensduur hebben dan stalen ringen. De overle-
vingskans van de Dodaars werd geschat op 0,60. Dit kwam goed
overeen met de uitkomsten van het populatiemodel. (DH)
Corresponding editor: Dik Heg
Received 12 July 2008; accepted 30 March 2009