Survival to first breeding is not sex-specific in the Coal Tit
J. Ornithol. 144, 148-156 (2003)
© Deutsche Ornithologen-GeseUschaft/Blackwell Verlag, Berlin
Survival to first breeding is not sex-specific in the Coal Tit (Parus ater)
Verena C. J. Dietrich 1' 2, Tim Schmoll 2, Wolfgang Winkel 3 and Thomas Lubjuhn 2
1Zoologisches Institut, TU Braunschweig, Fasanenstr. 3, D-38092 Braunschweig, Germany;
Email: [email protected];
2 Institut ftir Evolutionsbiologie und 0kologie, Rheinische Friedrich-Wilhelms-Universitfit Bonn,
An der Immenburg 1, D-53121 Bonn, Germany; (corresponding author; Email: [email protected])
3 AG Populations6kologie, Institut ftir Vogelforschung "Vogelwarte Helgoland', Bauernstr. 14,
D-38162 Cremlingen-Weddel, Germany
Differential survival of males and females affects the structure and dynamics of avian populations, but studying sex-specific survival rates is difficult. This is especially true for offspring if the period between hatching and first breeding is considered. Under certain
conditions, however, the determination of offspring sex ratio, recruitment and dispersal
may help in the investigation of sex-specific survival rates to the age of first breeding. Applying a molecular technique we sexed a large sample of Coal Tit (Parus ater) nestlings
from a nest box population in a coniferous forest near Lingen/Emsland (Lower Saxony,
Germany). The study covered a period of two years and included first and second broods.
We found that the sex ratio did not deviate from unity. Through capturing breeding adults
in the second year, we were able to examine local recruitment rates and natal dispersal distances of male and female offspring. The sexes differed significantly neither in recruitment
probability, which was generally high, nor in dispersal distance, which was generally low.
Our results indicate that there is no difference in the survival rate of male and female Coal
Tits during their first year of life. The relevance of our findings are discussed with regard
to the characteristics of the study population.
Keywords: molecular sex determination, offspring sex ratio, sex-specific recruitment, sex-specific dispersal, sex-specific survival, multiple breeding.
Zum Fehlen geschlechtsspezifischer Unterschiede im Uberleben bis zum ersten Brutjahr
bei der Tannenmeise (Parus ater)
Die Llberlebensrate von Individuen beeinflusst erheblich die Znsammensetzung und Dynamik von Vogelpopulationen. Von besonderem Interesse ist hierbei die Frage, ob sich die
Oberlebenswahrscheinlichkeit von Mfinnchen und Weibchen unterscheidet. Dies zu kl~iren, gestaltet sich besonders schwierig, wenn das Uberleben von Jungv6geln im ersten
Jahr betrachtet werden soll, da die Geburtsortstreue oftmals weniger ausgepr~igt ist als die
Brutortstreue. Unter gewissen Bedingungen k6nnen jedoch Untersuchungen zur geschlechtsspezifischen Rekrutierungsrate und zur Entfemung zwischen Geburts- und Bruth6hle Rtickschltisse auf die ()berlebensraten zulassen. Mittels molekularer Methoden
haben wir das Geschlecht von insgesamt 2243 Jungv6geln der Tannenmeise (Parus ater)
aus einer Nistkastenpopulation bei Lingen/Emsland (Niedersachsen) bestimmt. Die Unter-
U.S. Copyright Clearance Center Code Statement: 0021-8375/2003/14402-148 $ 15.00/0
Dietrich et al. • Survivalto first breedingin the Coal Tit
suchung erstreckte sich tiber zwei Jahre (2000 und 2001) und schloss im ersten Jahr 91
Erstbruten sowie 55 Zweitbruten und im zweiten Jahr 159 Erstbruten ein. Basierend auf
den Wiederfangraten im zweiten Jahr liegen sich Aussagen beztiglich der Geburtsortstreue
der Jungvrgel des Jahres 2000 treffen. Das Geschlechterverh~iltnis der Nestlinge war bei
einem M~innchen-Anteilzwischen 47,0 % und 53,8 % sowohl in beiden Jahren als auch in
Erst- und Zweitbruten ausgeglichen. Zudem unterschieden sich M~innchen und Weibchen
weder beztiglich der Geburtsortstreue, die generell sehr ausgepr~igt war (insgesamt 10,3 %
der untersuchten Jungvrgel konnten im Folgejahr als Brutvogel wiedergefangen werden),
noch im Hinblick anf die Distanz zwischen Geburts- und Bruthrhle, die generell sehr
niedrig war (durchschnittlich 549 + 299 m). Unter Berticksichtigung der Tatsache, dass
das Untersuchungsgebiet ftir die Tannenmeise ein optimales Habitat darstellt, deuten diese
Befunde darauf hin, dass sich die Oberlebensraten m~innlicherund weiblicher Tannenmeisen im ersten Lebensjahr nicht unterscheiden. Es muss jedoch often bleiben, ob sich diese
Schlussfolgerung ohne weiteres anf andere Populationen tibertragen l~isst.
Survival represents a basic component of individual fitness in animal populations. Whether
a bird survives to the subsequent breeding season or not matters not only in terms of reproduction but is also an important factor in population structure and population dynamics. In
this context it is of great interest to check
whether there are sex-specific differences in
survival as this may bias adult sex ratios. However, it remains difficult to examine survival
probabilities of individual birds within a population owing to mechanisms like dispersal. Recaptures or resightings are presumably incomplete so that capture-recapture statistical
models have come into use (for review Lebreton et al. 1992, 1993). The findings regarding
sex-specific survival in birds, however, are still
inconsistent. For example in the Great Tit (Parus major), a higher survival of males (e. g.
Orell & Ojanen 1979, Perrins & McCleery
1985), a higher survival of females (e. g. Hrrak
& Lebreton 1998) and no differences between
the sexes (Clobert et al. 1988) have all been reported.
In a species with high fidelity to the breeding site, like the Coal Tit (Parus ater; e. g.
Winkel 1981), a reliable estimate of the sexspecific survival rates of adult breeders from
one year to another is not very problematical.
The probability of emigration should be negligible and the local recapture rate therefore can
serve as an adequate measure of the survival
rate (Winkel 1984, Winkel & Winkel 1988,
1995). Studying the sex-specific survival of
offspring from hatching to the first breeding
season, however, turns out to be more difficult
as natal philopatry is usually low in the Coal
Tit (Winkel 1981). One way to tackle this
problem lies in the combined analysis of local
recruitment and natal dispersal with regard to
the sex of offspring. In this context it is also
necessary to determine the sex of most of the
nestlings hatched within a breeding season because sex-specific differences in recruitment
and/or dispersal will have contrasting effects
on the population structure, depending on
whether the offspring sex ratio is biased or balanced.
There is recent evidence for biased offspring
sex ratios in an increasing number of bird species (for review e. g. Godfray & Werren 1996,
Hardy 1997) but most of these analyses refer
to the brood level and not to the population
level, while only the latter is of interest in our
study. However, it should be noted that an
adaptive manipulation of the brood sex ratio in
response to environmental factors and/or parental quality could be shown in many species,
e. g. in the Great Tit (Lessels et al. 1996, Krlliker et al. 1999, Radford & Blakey 2000),
Journal ftir Ornithologie 144, 2003
with the mechanism of sex ratio adjustment
still remaining unclear (e. g. Krackow 1995,
The determination of offspring sex ratio is
complicated by the fact that in most bird species it is impossible to distinguish between
male and female nestlings by means of morphological features. Help was provided by the
development of molecular techniques for sexing birds, which make use of sequence differences in the sex chromosomes (males: homogametic [ZZ], females: heterogametic [ZW];
for review Lessels & Mateman 1996, Ellegren
& Sheldon 1997, Quinn 1999). In this study
we used a method developed by King & Griffiths (1994) to determine the sex of a large
sample of Coal Tit nestlings from first broods
of two years and second broods of one year. To
check whether differential mortality of male
and female offspring occurs during the nestling period, we distinguished between the "primary sex ratio" (defined as the sex ratio at egg
laying) and the "secondary sex ratio" (defined
as the sex ratio at blood sampling, nestling age
10-14 days). The determination of the primary
sex ratio is often difficult because of unhatched eggs or nestlings dying before blood
sampling, but in our study a large number of
broods were able to be sexed completely,
which allowed the calculation of the primary
sex ratio for this subsample.
Recaptures of nestlings as breeding adults in
the following year made it possible to examine
whether there are differences between the
sexes concerning local recruitment and natal
dispersal (cf. e. g. Winkel 1981, Orell et al.
1999). From these data conclusions concerning
the survival of male and female Coal Tit offspring in our study area are drawn.
We studied a nest box population of the Coal Tit, a
small hole-breeding passerine bird common in Europe (e. g. Glutz von Blotzheim & Bauer 1993), in a
mixed coniferous forest near Lingen/Emsland
(Lower Saxony, Germany). The 325 ha study area
contains about 560 nest boxes (for details on the
study area see Winkel 1975, Altenkirch & Winkel
1991), in which between 1990-2001 on average 113
Coal Tit pairs bred per year. The proportion of second broods is usually high (in the year 2000 it was
63.5 %), but can vary between 0-100 % in different
years (see Winkel 1975, Winkel & Winkel 1997).
In the years 2000 and 2001 all nestlings were
banded with unique numbered rings of the "Vogelwarte Helgoland" when they were 10-14 days old
and blood samples (approx. 50 gl) were taken from
the wing vein for molecular sex determination. During the breeding season 2001 we tried to capture all
adults while they were feeding the approximately
10-12 days old nestlings. Among these adult
breeders the recruits from the breeding season 2000
could be easily identified by their ring numbers. Natal dispersal distances were measured from the place
of birth to the subsequent breeding place by means
of standardised nest-site maps (accuracy + 10 m).
Molecular sex determination
The blood samples were diluted in 250 gl APS buffer (Arctander 1988) and stored at -20 °C until further analysis. DNA was isolated according to a
modified standard procedure (Lubjuhn & Sauer
For molecular sex determination we used a method developed by King & Griffiths (1994). This
method is based on a primer pair (RG 11 and RG 12,
for sequence information see King & Griffiths
1994) that amplifies a W chromosomal, i. e. femalespecific locus in the Coal Tit via polymerase chain
reaction (PCR). To monitor the amplificability of
each individual DNA sample (positive control) we
added another primer pair (2 KM-5 and 2 KM-3),
that was originally developed for microsatellite
analyses in the Great Tit, but amplifies an anonymous locus in Coal Tits, too (Gerken & Lubjuhn,
unpublished data). After PCR, agarose gel
electrophoresis (gel size 7 x l 0 c m , 2% agarose,
130 V/cm) and staining with ethidium bromide this
procedure results in only one visible fragment for
males and two distinct fragments for females.
PCR conditions were as follows: Approx. 100 ng
of genomic DNA were amplified in the presence of
the primers 2 KM-5 and 2 KM-3 (20 pmol each) as
well as primers RG 11 and RG 12 (5 pmol each).
Each PCR reaction additionally contained 200 p.M
dNTPs, 4 mM MgC1 and 0.25 U Taq polymerase.
Dietrich et al. • Survival to first breeding in the Coal Tit
however, that seem to allow molecular sexing in all
non-ratite bird species (see Ellegren 1996, Griffiths
et al. 1996).
Offspring sex ratios
Offspring brood sex ratio [proportion
Fig. 1. Distribution of offspring brood sex ratios
(proportion males) in (a) first broods of the breeding season 2000 (n = 91), (b) second broods of the
breeding season 2000 (n = 55) and (c) first broods
of the breeding season 2001 (n = 159). Sex ratios
were rounded to the first decimal place before being
Abb. 1. Verteilung der Geschlechterverh~iltnisse
innerhalb der Bmten (als Anteil Mgnnchen) in
(a) Erstbruten der Brutsaison 2000 (n = 91),
(b) Zweitbmten der Bmtsaison 2000 (n = 55) und (c)
Erstbruten der Brutsaison 2001 (n = 159). Die Geschlechterverhaltnisse wurden vor der graphischen
Darstellung auf eine Nachkommastelle gerundet.
Cycling conditions included initial denaturing for
4 min at 94°C, followed by 6 cycles of 30 s at
94 °C, 1 min at 66 (-1)°C and 40 s at 72 °C, and
then 28 cycles of 10 s at 94 °C, 20 s at 60 °C and 15
s at 72 °C. Final extension lasted 10 min at 72 °C.
It should be mentioned that the method described
above is only applicable in different species of the
genus Parus (King & Griffiths 1994, own unpublished data). Other primers have been identified,
In the breeding season 2000 we investigated
146 Coal Tit broods, in which 1177 nestlings
hatched. We determined the sex of 1107 of
these nestlings (94.1%), of which 750 were
from 9l first broods (96.5 % of nestlings hatched) and 357 from 55 second broods (89.3 %
of nestlings hatched). The remaining 70 nestlings died before blood sampling.
With 557 female and 550 male nestlings the
total offspring sex ratio was balanced (binomial test: p = 0.86). Analysing first and second
broods separately, we found that 47.7 % of the
first brood nestlings and 53.8 % of the second
brood nestlings were males (see Table l and
Fig. 1). These sex ratios did not deviate from
unity either (binomial tests; first broods: p =
0.23, second broods: p = 0.17).
The data presented above refer to the
secondary sex ratios as they include completely sexed broods (n = 56 first and 14 second broods) as well as only partially sexed
broods (n = 35 first and 41 second broods).
Disregarding the latter, i. e. calculating the primary sex ratio as defined in the introduction,
we obtained similar results: For all completely
sexed broods the proportion of male nestlings
was 48.6 % (295 out of 607; binomial test: p =
0.52), for completely sexed first broods 47.9 %
(binomial test: p = 0.37; see also Table 1) and
for completely sexed second broods 52.0 %
(binomial test: p = 0.77; see also Table l). In
addition, there was no evidence for sex-specific offspring mortality between blood sampling
and fledging as 11 of 21 sexed nestlings that
died before leaving the nest, were male (binomial test: p = 1.0).
Comparing the sex ratio between first and
second broods, no significant differences could
be found, neither regarding the primary sex
ratio (data see Table 1; likelihood ratio = 0.55,
Journal f'tir Omithologie 144, 2003
Table 1. Summary of the results derived from sexing a large sample of Coal Tit nestlings from first and
second broods of the year 2000 and first broods of the year 2001. Secondary sex ratio = sex ratio of nestlings
at age 10-14 days (time of blood sampling), primary sex ratio = sex ratio at egg laying (only broods with
number of eggs = number of young bled were considered). None of the sex ratios differed significantly from
a 50:50 expectation (exact p-values see text),
Tab. 1. Zusammenfassung zu den Ergebnissen der Geschlechtsbestimmung bei einer grogen Anzahl von
Tannenmeisennestlingen aus den Erst- und Zweitbruten des Jahres 2000 und den Erstbmten des Jahres
2001. Sekundtires Geschlechterverhfiltnis = Geschlechterverh~iltnis im Nestlingsalter von 10-14 Tagen
(Zeitpunkt der Blutentnahme), primfires GeschlechterverNiltnis = Geschlechterverh~iltnis zum Zeitpunkt
der Eiablage (es wurden nur Bruten berticksichtigt, bei denen die Anzahl der Eier = Anzahl der beprobten
Jungtiere war). Keines der Geschlechterverh~ltnisse wich signifikant yon einer 50:50-Erwartung ab (exakte
p-Werte s. Text).
secondary sex ratio
primary sex ratio
nestlings from first broods 2000
nestlings from second broods 2000
nestlings from first broods 2001
p = 0.46) n o r regarding the secondary sex ratio
(data see Table 1; likelihood ratio = 3.54, p =
In the b r e e d i n g season 2001 the sex of 1136
nestlings fi'om 159 first broods (98.0 % of all
hatched nestlings) was able to be determined
(there were only two second broods in that
year, w h i c h were disregarded in the analysis).
The results for the first broods were similar to
those obtained in the previous year with
49.9 % of the offspring being male (binomial
test: p = 0.98; see Table 1 and Fig. 1). 100
broods were sexed completely and therefore
represent the primary sex ratio, w h i c h did not
deviate from the expected 50:50 distribution
either, with 47.0 % of the nestlings b e i n g male
(binomial test: p = 0.10; see also Table 1).
In the breeding season 2001 we captured 114
breeding adults, which were born in the study
area the year before, of w h i c h 63 were females
and 51 males. Thus 10.3 % of young from
w h i c h blood samples were taken in the year
2000 recruited into the study population. Recruitment probabilities from first broods were
12.2 % (48 out of 392) for females and 11.7 %
(42 out of 358) for males, while recruitment
Proportion of male and female recruits
recaptured in the breeding season 2001. Offspring
from first and second broods are considered separately, since significantly more young recruited
from first compared to second broods (see also
Abb. 2. Anteil mfinnlicher und weiblicher Nachkommen, die in der Brutsaison 2001 wiedergefangen wurden. Jungv6gel aus Erst- und Zweithruten
sind getrennt aufgefiihrt, da Erstbruten signifikant
mehr geburtsortstreue Nachkommen erbrachten als
Zweitbmten (s. Text).
probabilities from second broods a m o u n t e d to
9 . 1 % (15 out of 165) for females and 4.7 % (9
out of 192) for males (see also Fig. 2). Since
we already k n e w that the total recruitment rate
Dietrich et al. - Survival to first breeding in the Coal Tit
from second broods in 2000 was significantly
lower than that from first broods (Schmoll et
al. in press), we fitted a logistic regression
model to the data in order to analyse whether
sex-specific differences in the recruitment
probabilities exist. Offspring sex and offspring
origin from first vs. second broods were included in the model as the predictors and local
recruitment as the binary response variable.
Neither offspring sex nor the interaction of offspring sex and origin was significantly related
to the recruitment probability (Z 2 = 2.39, p =
0.12 and Z 2 = 1.82, p = 0.18, respectively),
while the significant influence of offspring
origin (first vs. second brood) was confirmed
(Z 2 = 7.32, p = 0.007).
although second broods tended to contain
more male nestlings as shown by Lessels et al.
(1996) for the Great Tit.
For the 114 recruits the natal dispersal distance
was measured, which ranged from 30 m to
1395 m (mean + SD = 549 _+ 299 m). There
was no significant difference in the dispersal
distance between recruits from first broods
(mean + SD = 572 + 303 m, n = 90) and those
from second broods (mean _+ SD = 467 _+
275 m, n = 24; Mann-Whitney U-test: U =
864.0, p = 0.13). This was also the case if male
and female recruits were analysed separately
(data not shown). Thus we compared sex-specific dispersal distances without distinguishing
between first and second broods. Although females (mean _+ SD = 570 _+ 288 m, n = 63) dispersed slightly farther than males (mean + SD
= 525 _+ 314 m, n = 51), this difference turned
out to be non-significant (Mann-Whitney Utest: U = 1429.5, p -- 0.31).
In the Coal Tit population investigated the offspring sex ratio did not deviate from unity in
two subsequent years. Comparing first and
second broods within one breeding season,
there was no significant difference either,
There is no evidence for sex-specific mortality between egg laying and blood sampling
(age of young 10-14 days) in our study population, since both, the primary sex ratio and the
secondary sex ratio were balanced (compare
e. g. Lessels et al. 1996, Svensson & Nilsson
1996). Additionally, the nearly equal number
of male and female nestlings which died between blood sampling and fledging suggests
that there is no differential mortality before
fledging at all. But in this context it should be
noted that we do not know anything about embryo mortality in the egg. Summing up, however, our data indicate that the production of
male and female offspring within our population was not biased towards one sex from the
If as many male as female young are produced within one breeding season, this does
not inevitably mean that this relation still continues to exist until the next year. As a consequence of differential mortality or a differential probability of leaving their natal area,
more individuals of one sex may be found as
breeding adults in the next year's breeding season. However, in our study the local recruitment did not differ between the sexes, i. e. the
probability of breeding at the birth site was the
same for males and females.
In general, the overall recruitment rate was
extremely high with a tenth of the nestlings
breeding in their natal area in the following
season. Coal Tit nestlings have usually been
found to be not as faithful to their birthplace.
Over seven years Winkel (1981) reported an
average recruitment rate of about 2.9 % (range:
0.17-7.2 %) in the same area. Our value therefore seems to represent the upper end of a
highly variable scale.
Another result from this population not completely in line with previous findings is that
significantly fewer young recruited from second broods than from first broods. In his study
over seven years Winkel (1981) had found the
opposite and explained that in terms of a higher post-fledging mortality of the first brood
young (Winkel & Winkel 1988). Recruitment
rates, however, differ between years depending
on the conditions in the study area (see also
Winkel 1981) and especially post-fledging survival can be highly variable (e. g. Perrins &
McCleery 1985, Naef-Daenzer et al. 2001).
The most plausible explanation for our findings concerning the general recruitment rates
of first and second brood nestlings therefore is
that the conditions for Coal Tit nestlings from
the breeding season 2000 were extraordinary
good in our study area, especially for nestlings
from first broods. This would explain the generally high recruitment rate on one hand and
the higher recruitment rate of first brood nestlings on the other.
Most individuals which cannot be found
again the next year have either died or emigrated from the study area. Although studying
the extent of emigration is difficult, the measurement of disPersal distances within the area
may serve as an indicator for emigration probability. The average dispersal distance we
found was low (549 _+299 m) and only half of
the distance Winkel (1981) measured in his
long term study (1005 m). There was no significant difference in the dispersal distance of
males and females, although the average dispersal distance of the latter was 45 m higher.
Winkel (1981) found a very similar difference
(59 m) that was, however, statistically non-significant too. With respect to their sex-specific
dispersal behaviour, Coal Tits therefore seem
to differ from other species of the genus Parus,
in which statistically significant differences
between the sexes have been reported (e. g.
Great Tits, Winkel 1981; Siberian Tits Parus
cinctus, Orell et al. 1999).
In general, the extent of dispersal should depend on the conditions in the natal area. Our
study area probably represents an optimal habitat for Coal Tits, where they find excellent
breeding conditions (see e.g. Winkel 1975,
Winkel & Winkel 1987). Intra- and interspe-
Journal fur Ornithologie144. 2003
cific competition for nest boxes is not a major
point since there are enough nest boxes all
over the area which are not occupied. Thus this
coniferous forest has capacities ]'or further coal
tit breeding pairs, which was also indicated by
the fact that the population density in the
breeding season 2001 was more than 50%
higher than in the year 2000. All these aspects
(i. e. the high recruitment rates, the low dispersal distances and the increasing population
size from 2000 to 2001) make it improbable
that many individuals left this high quality area
during the period of our study.
Considered in connection, our results indicate that there are no differences in the survival rates between the sexes. But, in view of the
above arguments, this does not necessarily
mean that our results can be applied to other
Coal Tit populations. It is even possible that
we would find differences in other years with
worse conditions. Such differences, however,
would be of great interest because they can
throw some light on the influence of environmental factors on dispersal behaviour of male
and female nestlings.
This research was supportedby the Deutsche Forschungsgemeinschaft (Lu 572/2-3). We would like to thank G.
Rtippell for his support, S. Bleidissel, M. Orlaud and C.
Wallnischfor theirhelp in the laboratory,H. and K. K6rner
for housingand hospitalityduringfield work and J. Brtin,
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Accepted: 10 October2002