Variation in haematological indices and immune function during the annual cycle in the Great Tit Parus major
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ABSTRACT: Exposing vertebrates to pathogenic organisms or inflammatory stimuli, such as bacterial lipopolysaccharide (LPS), activates the immune system and triggers the acute phase response. This response involves fever, alterations in neuroendocrine circuits, such as hypothalamo-pituitary-adrenal (HPA) and -gonadal (HPG) axes, and stereotypical sickness behaviors that include lethargy, anorexia, adipsia, and a disinterest in social activities. We investigated the hormonal, behavioral, and thermoregulatory effects of acute LPS treatment in a seasonally breeding songbird, the white-crowned sparrow (Zonotrichia leucophrys gambelii) using laboratory and field experiments. Captive male and female sparrows were housed on short (8L:16D) or long (20L:4D) day lengths and injected subcutaneously with LPS or saline (control). LPS treatment activated the HPA axis, causing a rapid increase in plasma corticosterone titers over 24 h compared to controls. Suppression of the HPG axis occurred in long-day LPS birds as measured by a decline in luteinizing hormone levels. Instead of a rise in body temperature, LPS-injected birds experienced short-term hypothermia compared to controls. Birds treated with LPS decreased activity and reduced food and water intake, resulting in weight loss. LPS males on long days experienced more weight loss than LPS males on short days, but this seasonal effect was not observed in females. These results paralleled seasonal differences in body condition, suggesting that modulation of the acute phase response is linked to energy reserves. In free-living males, LPS treatment decreased song and several measures of territorial aggression. These studies highlight immune-endocrine-behavior interrelationships that may proximately mediate life-history tradeoffs between reproduction and defense against pathogens.Hormones and Behavior 02/2006; 49(1):15-29. · 3.74 Impact Factor
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ABSTRACT: Hypotheses of hemoparasite-mediated sexual selection and reproductive costs rely on the assumption that avian blood parasite infections are harmful to their hosts. To test the validity of this assumption, we examined the health impact of Haemoproteus blood parasites on their great tit (Parus major) host. We hypothesised that if blood parasites impose any serious health impact on their avian hosts, then infected individuals must differ from uninfected ones in respect to hemato-serological general health and immune parameters. A 3-year study of two great tit populations, breeding in contrasting (urban and rural) habitats in south-east Estonia, revealed that Haemoproteus blood parasites affected the health state of their avian hosts. Infected individuals had elevated lymphocyte hemoconcentration and plasma gamma-globulin levels, indicating that both cell-mediated and humoral immune response mechanisms are involved in host defence. The effect of parasites on cell-mediated immunity was both age- and sex-specific, as infection status affected peripheral blood lymphocyte counts only in males, and among these, the magnitude of response was greater in old individuals than yearlings. Heterophile hemoconcentration and plasma albumin levels were not affected by infection status, suggesting that blood stages of Haemoproteus infection do not cause a severe inflammatory response. Parasitism was not related to hematocrit values, indicating that Haemoproteus infection does not cause anemia. In two years, infected individuals were heavier than uninfected ones in the urban but not in the rural study area. This suggests, that under certain circumstances (possibly related to reproductive tactics), breeding great tits may avoid losing body mass in order to save resources for an anti-parasite immune response.Oecologia 09/1998; 116(4):441-448. · 3.01 Impact Factor
- Origin-related, environmental, sex, and age determi-nants of immunocompetence, susceptibility to ectopara-sites, and disease symptoms in the barn owl..
Studies on birds and mammals indicate that seasonal
variation in haematological variables and immune de-
fence is the rule rather than an exception (Hasselquist
et al. 1999, Nelson et al. 2002, Lozano & Lank 2003,
Møller et al. 2003, Fair et al. 2007, Buehler et al.
2008a). However, results are contradictory (e.g. Nelson
et al. 2002, Møller et al. 2003) for multiple reasons.
First, the activity of the immune system is frequently as-
sessed by measuring only one aspect, or by using only a
restricted number of variables to assess different
branches of the defence system (e.g. Gonzalez et al.
1999, Hasselquist et al. 1999, Christe et al. 2002,
Lozano & Lank 2003, Martin et al. 2004; but see Roulin
et al. 2007 and Buehler et al. 2008a as exceptions).
Immune responses are extremely complex, reflecting
the need to protect the host against a plethora of
pathogens (Nelson et al. 2002). Moreover, trade-offs
between different immune branches can arise (Ardia
2007), and an increase in one measure may evoke a re-
duction in another. Second, the sampling period may
be too short or sampling is too infrequent to describe
seasonal changes in the physiological condition and im-
mune activity effectively (e.g. Hõrak et al. 1998a,
Gonzalez et al. 1999, Hasselquist et al. 1999, Christe et
Variation in haematological indices and immune function
during the annual cycle in the Great Tit Parus major
Pap P.L., Vágási C.I., Tökölyi J., Czirják G.Á. & Barta Z. 2010. Variation in
haematological indices and immune function during the annual cycle in the
Great Tit Parus major. Ardea 98: 105–112.
We investigated seasonal variation in haematological indices and immune
function in the non-migratory Great Tit Parus major over a complete annual
cycle. The haematocrit value showed a marked reduction in spring and sum-
mer, reaching a lowest value during moult, after which it increased to reach a
maximum in winter and spring. The peak in the heterophil to lymphocyte ratio
(H/L) during July indicated that Great Tits were the most stressed during the
first half of the moulting period. The increase in heterophils and H/L ratio, con-
current with a reduced number of lymphocytes during the breeding season,
probably reflected the cost of reproduction in terms of physiological stress and
immune suppression. After breeding the number of heterophils and the H/L
ratio decreased, reaching a lowest value during winter. The concentration of im-
munoglobulins followed the seasonal pattern in the number of heterophils,
though highest values occurred somewhat later, in July–September during the
second part of the moulting period. Our observations indicated large differ-
ences in activity throughout the year of different components of the immune
system. This suggests differences in function among the components and pos-
sibly differences in susceptibility to stress, parasitism and hormones during the
annual cycle. When juveniles became independent of their parents, the im-
munoglobulin concentration increased, whereas other immune measures did
not show a significant change. This indicates a rapid increase of at least one
component of the immune system after the young fledge.
Key words: annual cycle, haematocrit, health state, immunity, immunoglobulins,
Parus major, white blood cells
1Dept Taxonomy and Ecology, Babes ,-Bolyai University, RO–400006 Cluj
Napoca, Clinicilor Street 5–7, Romania; 2Behavioural Ecology Research
Group, Dept Evolutionary Zoology, University of Debrecen, H–4032 Debrecen,
Egyetem tér 1, Hungary; 3Dept Infectious Diseases, Faculty of Veterinary
Medicine, University of Agricultural Sciences and Veterinary Medicine,
RO–400372 Cluj-Napoca, Ma
*corresponding author (email@example.com)
vs ,tur Street 3–5, Romania;
Péter L. Pap1,2, Csongor I. Vágási1,2,*, Jácint Tökölyi2, Gábor Á. Czirják3& Zoltán Barta2
al. 2002, Pap 2002, Owen-Ashley et al. 2006). In con-
trast, Buehler et al. (2008a) followed the change in
concentration and activity of several immune indices of
the Red Knot Calidris canutus, a long-distance migrato-
ry species, during the complete annual cycle. This sets a
yardstick with which to compare birds with contrasting
life histories. For example, sedentary and migratory
species may differ in exposure to environmental stress,
like parasitism, energetic expenditure, food supply and
temperature, which may result in divergent selection
on immune functions during the annual cycle.
Our main objective is to describe seasonal variation
in haematological indices and immune function under
field conditions in the Great Tit Parus major, one of
Europe’s most common non-migratory species. Under-
standing the seasonal variation in the haematological
indices and immune function of temperate zone birds is
important to make a comparison with species with dif-
ferent life histories (see Buehler et al. 2008a). Because
of the sex-specific energetic, physiological and behav-
ioural costs of maintaining an effective immune system
(Sheldon & Verhulst 1996, Lochmiller & Deerenberg
2000), we expect a difference in immune functions be-
tween males and females during the annual cycle
(Hasselquist 2007, Martin et al. 2008). We explore
therefore sex effects in the activity of the immune sys-
tem. In addition, we investigate the way individuals ac-
quire a mature defence system during ontogeny, by
recording the haematological variables and immune
function of the same individuals throughout the
nestling and independence period. We expect that due
to the rapid development of Great Tit nestlings, im-
mune measures promoting defence increase rapidly
during independence (Buehler et al. 2009). We think
our observations provide new insights in the develop-
ment of the immune system in wild birds as most of our
knowledge in this field comes from studies on birds in
captivity and poultry (Ardia & Schat 2008).
Study site, studied species and captures
We studied a local Great Tit population in the sur-
roundings of the village Stana (46°89'N, 23°14'E,
Transylvania, central Romania) between April 2004
and March 2006. The study site is situated in a 40 ha
orchard of several species of old fruit trees. Pastures
and arable fields surround the orchard. Great Tit has an
annual cycle typical for most European non-migratory
species. It starts breeding during the second part of
April, and the nestlings fledge generally until the end of
June. In 2004, Great Tits fledged between 22 May and
6 June, and in 2005 between 18 May and 17 June.
After breeding, adult birds perform their annual com-
plete post-breeding moult, which may last several
months between June and September (Pap et al. 2007).
Juveniles, which fledge between June and July, replace
some of the remiges and all rectrices, and their body
feathers and wing coverts during the moulting period.
The temporal dynamics of the partial post-juvenile
moult is similar to that of the adults. In September,
birds start to form winter flocks, indicating the prepara-
tion for the winter (Cramp & Perrins 1993).
During the study period we regularly captured and
ringed birds by using mist nets (Ecotone, Poland)
which resulted in 455 captures, including 135 recap-
tures. Age and sex (when possible based on plumage
characters) were scored following Svensson’s (1992)
criteria, where ‘juveniles’ are birds before their first
complete post-breeding moult, and ‘adults’ are those
after the moult. In this way, ‘juveniles’ include second-
year birds, which are reproductively active without hav-
ing completed moult yet. Sample sizes of the haemato-
logical and immune indices are variable, depending on
the number of sampled birds. During the winter, we
used sunflower as bait to increase the number of cap-
tured birds. The bait was provided several days before
capturing and we stopped feeding after the capture ses-
sion. In this way, we minimized the confounding effect
of supplemental feeding on the physiology of the birds.
At capture we ringed, aged and sexed the birds, and we
measured tarsus length, wing length, and body mass.
In the winter of 2004, we mounted 180 nestboxes
in the orchard to study the breeding biology of Great
Tits. In 2004 and 2005, we followed 14 and 10 success-
ful broods, respectively. We followed the nests by al-
most daily visits to determine date of clutch initiation,
clutch size, hatching date, brood size, fledging date and
number of fledglings. In order to study the change in
the haematological indices and immune function dur-
ing ontogeny, we measured the nestlings and took
blood samples (as described below) at the age of 15
days, and subsequently after independence we recap-
tured as many fledglings as possible.
We collected blood samples (within 20 min after cap-
ture to avoid stress-induced immunosuppression; see
Buehler et al. 2008b) for analyses in a capillary tube
(70 µl) from the brachial vein. A drop of blood was
smeared on a slide, air-dried, fixed in absolute
methanol, and stained with May–Grünwald and
Giemsa. The haematocrit value was obtained by cen-
ARDEA 98(1), 2010
Pap et al.: IMMUNE FUNCTION OVER THE ANNUAL CYCLE OF GREAT TITS
trifugation of heparinized capillary tubes for 10 min at
10 000 RPM. After the haematocrit was determined,
plasma was separated from blood cells and stored at
–20°C until analysis. Smears were examined at 1000×
magnification and the proportion of different types of
leukocytes was assessed on the basis of examination of
100 leukocytes. The number of white blood cells was
expressed per approximately 10 000 erythrocytes. We
excluded monocytes, eosinophils and basophils from
the analyses because of their low concentration (less
than 10 cells/10 000 erythrocytes). The counts of the
white blood cells were made by the same person, and
these proved to be highly repeatable (see Pap 2002).
Total leukocyte counts (WBC) and the composition of
leukocytes are considered as indicators of the health
status, parasitic infestation and stress (Ots et al. 1998).
Leukocytosis (increase in the number of leukocytes) is
most commonly attributed to infectious diseases
(Fudge 1989). Heterophils are non-specific phagocytic
immune cells, and as parts of the innate immune de-
fence they play an important role during the initial
stages of most infections. Increased level of heterophils
is most common during inflammation, and it is a non-
specific response to foreign invasion or tissue damage.
Lymphocytes are highly specific immune cells, and they
are the main cell types in the adaptive immune re-
sponse (i.e. B-cells and T-cells). Decreasing lymphocyte
levels may indicate immunosuppression, while they
proliferate during infections (Ots et al. 1998). The het-
erophil to lymphocyte ratio (H/L) is widely used as an
indicator of stress (Davis et al. 2008), and the measure
is known to increase under stressful conditions.
Due to an accident, the plasma collected in February
2006 was lost, which left samples of 11 months to ana-
lyze for immunoglobulins. Immunoglobulins, being
part of the humoral immune system, play an important
role in innate and acquired immune response (Roitt et
al. 1996). Increase in immunoglobulin concentration in
the peripheral blood is related to parasite infestations
(de Lope et al. 1998, Ots & Hõrak 1998, Szép & Møller
1999). Total immunoglobulin includes circulating
IgG molecules with a role in first-line defence against
pathogens (Tizard 2004). We quantified the im-
munoglobulin concentration by spectrophotometry
(Khokhlova et al. 2004). Concentrations as low as
24 mg/l of heavy metal salts precipitate the immuno-
globulin, since the electric charge and colloidal stability
of gamma globulins are lower than those of serum al-
bumins at pH 7.4. We mixed 3.3 µl of plasma with
196.7 µl of 0.024% barbital buffer zinc sulphate solu-
tion and allowed immunoglobulins to precipitate for 30
min at room temperature (22–23°C). Immunoglobulin
concentration expressed in optical density units (ODU)
was read by spectrophotometer (λ = 475 nm, d = 0.5
cm) (Pap et al. 2008).
Data were analyzed by fitting linear mixed effect models
with individual birds as random factor (the ‘lme’ func-
tion of the R interactive statistical environment; R
Development Core Team 2005), thus controlling for the
effect of pseudo-replication caused by the recaptures.
Because the sex of juveniles was not determined, the ef-
fect of age, sex and the interaction was not tested simul-
taneously in the same model. Therefore, we first fitted a
model with month and age as explanatory variables. In
a next model, we analyzed the effect of sex of adult
birds. Because of the low sample size of adult females in
some months we pooled data into three seasons (breed-
ing: March–June, moulting: July–October, wintering:
November–February). In this analysis, the denominator
degrees of freedom are different for season and sex be-
cause season is inner to individual, i.e. its value can
change within individual (the random effect), while sex
is outer to individual, i.e. it cannot change within indi-
vidual (Pinheiro & Bates 2000, p. 91). Both month and
age are inner to individual, so they have the same de-
grees of freedom. Data of immunoglobulins, hetero-
phils, H/L ratio were log-transformed to fit the distribu-
tional assumptions of the linear models. The difference
in immune measures between adult males and females
and nestling was tested using one-way ANOVAs with
planned comparison of least square means, and Tukey
post-hoc tests for unequal sample size was used to test
the difference between specific groups. We found no sig-
nificant difference in morphological and physiological
variables of the nestlings born in 2004 and 2005, and
therefore the effect of year was omitted in the analyses
about the immune function of nestlings and fledglings.
Means are presented ±SD.
Seasonal variation in the haematological indices
and immune function
Haematocrit value varied significantly over the annual
cycle (Table 1, Fig. 1A), but was not affected by sex or
age. Haematocrit decreased during the breeding sea-
son, and after reaching a lowest value during the
moulting period in August it increased in autumn,
reaching a highest value in winter and spring. The sig-
nificant interaction between month and age indicates a
difference between adults and juveniles in the pattern
of haematocrit during the annual cycle. WBC, het-
erophils, lymphocytes, H/L ratio and immunoglobulin
concentration were similar between age classes and
sexes (Table 1), also indicated by the absence of signifi-
cance in the month × sex and month × age interactions.
WBC did not change significantly during the year
(Table 1), while lymphocytes, heterophils and the H/L
ratio showed a marked variation through the annual
cycle (Table 1, Fig. 1B,C,D). The number of heterophils
and H/L increased during the breeding and beginning
of the moulting season, from April until July, reaching
the highest value during the first half of the moulting
season in July. During August to November, when Great
Tits perform their annual moult and prepare for the
winter, the number of heterophils and the H/L ratio de-
creased, reaching a lowest value during the winter. The
number of lymphocytes showed an opposite pattern
with lowest values during the end of breeding and be-
ginning of moult in June. The immunoglobulin concen-
tration showed significant seasonal variation (Table 1,
Fig. 1E) with a marked increase throughout breeding
and moulting, and reaching a highest value during the
second part of the moulting period in September.
Subsequently, immunoglobulin decreased during au-
tumn, and reached a lowest value in winter.
Changes during independence of juveniles
The haematocrit level of nestlings was significantly
lower than in parents and the immunoglobulin concen-
tration was significantly higher than in adult females
(Table 2; planned comparison between adults and nest-
lings, haematocrit: F1,64= 41.88, P<0.0001, immuno-
globulins: Tukey post-hoc test for unequal sample size
between nestlings and adult females, P<0.001). WBC,
ARDEA 98(1), 2010
heterophil to lymphocyte ratio
F A MJJASO ND
(optical density units)
FA MJJAS O ND
lymphocytes / 104 red blood cells
heterophils / 104 red blood cells
Figure 1. Haematocrit level (A), lymphocyte number (B), heterophil number (C), H/L ratio (D) and total immunoglobulin concen-
tration (E) in the Great Tit during the annual cycle. Indicated are mean values ±SE. In case of haematocrit, open circles indicate ju-
veniles and closed circles adults.
Pap et al.: IMMUNE FUNCTION OVER THE ANNUAL CYCLE OF GREAT TITS
Adults and juvenilesAdults
Month × Age
Month × Age
Month × Age
Month × Age
Month × Age
Month × Age
Season × Sex
Season × Sex
Season × Sex
Season × Sex
Season × Sex
Season × Sex
Table 1. Haematocrit level, WBC, heterophil and lymphocyte number, H/L ratio and total immunoglobulin concentration in the
Great Tit in relation to month, age and sex of adult birds, by linear mixed effect models (see also Methods).
51.4 ± 2.4 (24)
111.6 ± 21.5 (19)
74.1 ± 20.3 (19)
32.3 ± 8.3 (19)
0.46 ± 0.15 (19)
0.054 ± 0.020 (24)
50.4 ± 2.7 (22)
109.9 ± 29.1 (19)
75.0 ± 19.7 (19)
31.6 ± 18.1 (19)
0.43 ± 0.23 (19)
0.088 ± 0.041 (22)
44.6 ± 5.4 (21)
108.2 ± 4.1 (21)
72.6 ± 3.4 (21)
28.8 ± 1.4 (21)
0.40 ± 0.02 (21)
0.074 ± 0.013 (21)
Table 2. One-way ANOVAs comparing haematological and immunological parameters of adult Great Tits during the breeding period
and their nestlings (15 days old). Given are means ±SD with sample sizes in parentheses.
45.9 ± 4.6
107.5 ± 4.3
72.0 ± 3.8
28.9 ± 1.1
0.40 ± 0.02
0.076 ± 0.014
44.9 ± 3.2
108.1 ± 17.6
71.9 ± 14.4
30.4 ± 6.5
0.43 ± 0.12
0.098 ± 0.029
Table 3. Change in the haematological and immunological parameters between the nestling and fledgling stage of individual Great
Tits (n = 12). Birds were recaptured 62 ± 47.3 days after initial measurements. Paired sample t-test, the values are means ±SD.
heterophils, lymphocytes and the H/L ratio were similar
between parents and nestlings. During the 62 ± 47.3
days between the first measure as nestlings and the sec-
ond measure as fledglings the immunoglobulin concen-
tration increased significantly (Table 3). The haemat-
ocrit, WBC, heterophils, lymphocytes and H/L ratio did
not change during this period. These results about the
haematological indices and immune function during in-
dependence could not been confounded by fledging
date, since none of the measures were related to fledg-
ing date (all P>0.4), which discounts a possibility of
confounding date effects.
We showed that haematological indices and immune
function fluctuate during the annual cycle of the non-
migratory Great Tit with large variation in pattern
among the measures. This variation probably reflects
different functions and susceptibility to stress, para-
sitism, energy supply or hormones. Some of the
changes, as the increased heterophil and immunoglob-
ulins concentration during summer, correspond to what
has been called the ‘breeding season – high exposure’
hypothesis (Hasselquist 2007), i.e. an enhancement of
the immune activity during spring and breeding as a re-
sult of the adaptive response of the immune system to
the seasonally emerging parasites’ attacks. On the other
hand, the opposite pattern of lymphocytes with high
numbers in winter is in favour of the hypothesis of a
hormonal and energetical incompatibility of the im-
mune function with reproduction (Hasselquist 2007,
Martin et al. 2008). Careful experiments about the sus-
ceptibility and function of different branches of the im-
mune system would clarify the mechanism responsible
for the seasonality of the immune indices that we ob-
served. Our results of differential seasonal patterns
among immune functions correspond to the conclusion
by Buehler et al. (2008a) who arrived at the same con-
clusion based on observations in the long-distance mi-
gratory Red Knot. There is a striking similarity in the
pattern of heterophils and lymphocytes between Great
Tit and Red Knot, suggesting that some common fac-
tors are responsible for mediating the variation of these
immune indices in migratory and sedentary birds.
Haematocrit is an indicator of the oxygen carrying
capacity of the blood, and increases as a response to el-
evated metabolic activity. The marked increase during
the autumn and winter might be explained by the
preparation of birds to the cold winter by enhancing
the oxygen carrying capacity of the blood, the increased
locomotor activity of the birds as the moulting season
ends, and dehydration (Fair et al. 2007). The observed
decrease of haematocrit during breeding with a low
during moulting is in accordance with the general pat-
tern in birds (Fair et al. 2007), and can be explained by
the reduced oxygen need of the organism due to in-
creased ambient temperature (Fair et al. 2007).
Our observation of an increase in the H/L ratio dur-
ing the breeding and early moulting period is consistent
with previous studies (Gustafsson et al. 1994, Christe et
al. 2002, Pap 2002; but see Hõrak et al. 1998a). The
shift is the result of an increase in the number of het-
erophils and a concomitant decrease in the number of
lymphocytes (see also Hõrak et al. 1998a) as the breed-
ing season progresses. This increase in the H/L ratio
may stem from stressful parental activity during breed-
ing (Hõrak et al. 1998b, Ilmonen et al. 2003). Likewise,
the increase in the number of heterophils, and H/L
ratio, during breeding can be related to the increase in
the number of micro- and macroparasites (e.g. Fudge
1989, Ots et al. 1998) as the level of infestation gener-
ally increases with a progressing breeding season (e.g.
Christe et al. 2002, Cosgrove et al. 2008).
The drop in number of heterophils and the H/L
ratio during moulting up to a low in autumn and win-
ter might be related to a relaxation of energetic stress, a
suppression or downregulation of the immune system
due to the energetically challenging low temperature
(Demas & Nelson 1996, Råberg et al. 1998, Svensson et
al. 1998), or to the absence of parasites during winter
(Cosgrove et al. 2008). Another interesting pattern in
the seasonality of leukocytes is that during summer the
number of lymphocytes is low while the heterophils
and the concentration of immunoglobulins is raised,
followed by an opposite change in the number and con-
centration of these measures in the subsequent period.
This finding may indicate a trade-off between different
immune branches suggesting that when one part of the
immune system is challenged the other part is down-
regulated. Such a trade-off was found in Tree Swallows
Tachycineta bicolor (Ardia 2007). Individuals that
mounted a strong response against phytohaemagglu-
tinin, which stimulates the cellular and innate compo-
nent of the immune system, had reduced humoral anti-
body response against sheep red blood cells.
The observed increase in immunoglobulin concen-
tration during breeding is in accordance with previous
studies on birds (e.g. Gustafsson et al. 1994, Christe et
al. 2002), but it contradicts the decrease in immuno-
globulin concentration between pre-laying and nesting
in another Great Tit population (Hõrak et al. 1998a).
Contrary to trends in the number of heterophils and
ARDEA 98(1), 2010
Pap et al.: IMMUNE FUNCTION OVER THE ANNUAL CYCLE OF GREAT TITS
H/L ratio, immunoglobulins concentration continued
to increase until the end of the moulting season in
September, after which it dropped to a low during win-
ter. This drop might have a similar basis as the drop in
heterophils and H/L ratio in winter as discussed above.
Finally, we found that within a short period of time
nestlings acquired a haematological profile and immune
function that was close to that of their parents. The
number of different leukocytes was similar in nestlings
and their parents, while immunoglobin concentration
increased following fledging, reaching the concentration
of adults characteristic to this period. Buehler et al.
(2009) observed similar changes with age in natural an-
tibodies in the Red Knot, suggesting the generality of a
rapid ontogeny of the immune system following fledg-
ing in birds.
To summarize, we found that (1) components of the
immune system exhibit different patterns during the
annual cycle, (2) the immune components measured
are similar between the sexes, and (3) juveniles obtain
an immune profile similar to adults, seemingly reflect-
ing a rapid ontogeny of the immune system. Because
the primary function of the immune system is defence,
a next step in immunoecological studies should be to
determine the role of different components of immuni-
ty in protection against specific parasite challenges
(Adamo 2004) in order to understand more profoundly
the annual cycle of a given immune variable. Further,
the cause and consequence of variation of haematologi-
cal condition and immune function remains to be test-
ed experimentally. Our results about the seasonality of
haematological and immunological indices may serve
as a framework for further research studying the mech-
anisms responsible for the variation in physiological
condition in birds.
We are grateful to Miklós Bán, Réka Kiss, István Kovács, Eszter
Ruprecht, Marina Spinu, Zsuzsanna Takács, and Tivadar Vinkler
who assisted in data collection and in the analysis of blood
samples. This work was financially supported by a Marie Curie
European Reintegration Grant (contract no. 005065) to ZB,
OTKA Grants (T046661, NF061143), and by the Hungarian and
Romanian Government, grant TéT (RO–32/05). PLP was sup-
ported by an OTKA grant (NF 61143) to ZB and by a research
grant (CEEX ET 94/2006) of the Romanian Ministry of
Education and Research, JT was aided by an István Apáthy
Association student research grant, CIV was supported by a PhD
scholarship from the Hungarian Ministry of Education and
Culture, and GÁC was sponsored by a research grant (CNCSIS Td
368/2006) of the Romanian Ministry of Education and Research.
Field measurements comply with the current Romanian laws.
Two anonymous referees kindly provided constructive criticism.
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Het onderhoud van het inwendig afweersysteem van vogels kost
energie en bouwstoffen. Vogels bezuinigen hierop zodra dat mo-
gelijk is. Daarom is te verwachten dat de activiteit van het af-
weersysteem, afhankelijk van de ‘afweging’ van kosten en baten,
aan fluctuaties onderhevig is. Gedurende twee jaren werd in
Centraal-Roemenië bij Koolmezen Parus major bloed geprikt om
te onderzoeken hoe sterk deze fluctuaties zijn. De bloedmon-
sters werden onderzocht op de hematocrietwaarde (gehalte aan
rode bloedcellen), de aantallen van twee typen witte bloedli-
chaampjes (heterofielen en lymfocyten), de verhouding tussen
deze twee (een maat voor de mate van stress waaraan de vogel
is blootgesteld) en de concentratie aan afweerstoffen (immuno-
globulines). De hematocrietwaarde nam in het voorjaar en de
zomer sterk af, bereikte in de nazomer tijdens de rui een diepte-
punt en nam daarna weer toe tot een piek in de winter en het
voorjaar werd bereikt. De H/L-verhouding (toename aantal
heterofielen, afname lymfocyten) was het hoogst in juli, tijdens
de eerste helft van de ruiperiode. De toename van de H/L-ver-
houding in de loop van het broedseizoen is waarschijnlijk een
weerspiegeling van de verhoogde stress waaronder de vogels tij-
dens die periode leefden. Bovendien kan hierbij een rol ge-
speeld hebben dat de werking van het afweersysteem wordt
onderdrukt om voldoende energie vrij te maken voor bijvoor-
beeld het voeren van de jongen. Na het broedseizoen keerden
de aantallen heterofielen en lymfocyten, evenals de H/L-ver-
houding weer terug naar het niveau van vóór het broedseizoen.
Het gehalte aan immunoglobulines vertoonde een seizoenpa-
troon dat veel leek op dat aan heterofielen. Uit het onderzoek
blijkt dat Koolmezen door het jaar heen een zeer variabel af-
weersysteem hebben, waarbij grote verschillen in patroon tus-
sen de afzonderlijke onderdelen van het afweersysteem bestaan.
De oorzaak van deze verschillen blijft in dit beschrijvend onder-
zoek duister, maar vermoed wordt dat elke component een
eigen gevoeligheid voor stress, parasieten en hormonen heeft.
Na het uitvliegen van de jongen veranderde opmerkelijk weinig
in de samenstelling van het bloed. Alleen het gehalte van immu-
noglobulines liet een toename zien.(BIT)
Corresponding editor: B. Irene Tieleman
Received: 6 April 2009; accepted 15 February 2010