body temperature and breath rate in response to handling stress
body temperature and breath rate in response to handling stress
body temperature and breath rate in response to handling stress
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Physiology & Behavior 82 (2004) 905–912<br />
Shy <strong>and</strong> bold great tits (Parus major): <strong>body</strong> <strong>temperature</strong><br />
<strong>and</strong> <strong>breath</strong> <strong>rate</strong> <strong>in</strong> <strong>response</strong> <strong>to</strong> h<strong>and</strong>l<strong>in</strong>g <strong>stress</strong><br />
Claudio Carere a, *, Kees van Oers b<br />
a Department of Animal Behaviour, University of Gron<strong>in</strong>gen, The Netherl<strong>and</strong>s<br />
b Department of Population Biology of Animals, Centre for Terrestrial Ecology, Netherl<strong>and</strong>s Institute of Ecology (NIOO-KNAW), Heteren, The Netherl<strong>and</strong>s<br />
Received 2 June 2004; received <strong>in</strong> revised form 23 July 2004; accepted 29 July 2004<br />
Abstract<br />
A st<strong>and</strong>ard h<strong>and</strong>l<strong>in</strong>g pro<strong>to</strong>col was used <strong>to</strong> test the hypothesis that boldness predicts <strong>stress</strong> responsiveness <strong>in</strong> <strong>body</strong> <strong>temperature</strong> <strong>and</strong><br />
<strong>breath</strong> <strong>rate</strong>. Great tit (Parus major) nestl<strong>in</strong>gs were taken from the field, h<strong>and</strong> reared until <strong>in</strong>dependence, <strong>and</strong> their <strong>response</strong> <strong>to</strong> a novel<br />
object was assessed. At the age of 6 months, dur<strong>in</strong>g the active phase (daytime), <strong>body</strong> <strong>temperature</strong> was recorded <strong>and</strong> <strong>breath</strong> <strong>rate</strong> was<br />
counted immediately after capture <strong>and</strong> after 5 m<strong>in</strong> of quiet rest <strong>in</strong> a bag. A second group of birds of two l<strong>in</strong>es bidirectionally selected for<br />
the same trait was tested dur<strong>in</strong>g the <strong>in</strong>active phase (nighttime). Dur<strong>in</strong>g the active phase, <strong>body</strong> <strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong> were higher <strong>in</strong><br />
the first than <strong>in</strong> the second measurement. In the second measurement, shy <strong>in</strong>dividuals showed higher <strong>body</strong> <strong>temperature</strong> than bold<br />
<strong>in</strong>dividuals. In the <strong>in</strong>active phase, values of both parameters were lower than <strong>in</strong> the active phase. Body <strong>temperature</strong> was lower <strong>in</strong> the first<br />
measurement than <strong>in</strong> the second measurement <strong>and</strong> no l<strong>in</strong>e difference emerged. Breath <strong>rate</strong> was higher <strong>in</strong> shy than <strong>in</strong> bold <strong>in</strong>dividuals <strong>and</strong><br />
did not differ between the two measurements. Females had higher <strong>body</strong> <strong>temperature</strong>s than males, probably due <strong>to</strong> their lower weight,<br />
because <strong>body</strong> <strong>temperature</strong> was negatively correlated with <strong>body</strong> mass. The results <strong>in</strong>dicate that <strong>body</strong> <strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong> are<br />
<strong>in</strong>dica<strong>to</strong>rs of acute <strong>stress</strong> <strong>in</strong> songbirds <strong>and</strong> that differences <strong>in</strong> personality traits dur<strong>in</strong>g the juvenile phase are reflected <strong>in</strong> differential <strong>stress</strong><br />
responsiveness later <strong>in</strong> life.<br />
D 2004 Elsevier Inc. All rights reserved.<br />
Keywords: H<strong>and</strong>l<strong>in</strong>g <strong>stress</strong>; Cop<strong>in</strong>g; Boldness; Personality; Breath <strong>rate</strong>; Body <strong>temperature</strong>; Sex differences; Birds<br />
1. Introduction<br />
In birds, st<strong>and</strong>ardised h<strong>and</strong>l<strong>in</strong>g pro<strong>to</strong>cols have been<br />
widely used <strong>to</strong> assess the hypothalamus–pituitary–adrenal<br />
(HPA) axis <strong>response</strong>. In most species, the rise <strong>in</strong> glucocorticoids<br />
occurs with<strong>in</strong> 3 m<strong>in</strong> follow<strong>in</strong>g h<strong>and</strong>l<strong>in</strong>g [1]. Recent<br />
studies have shown that birds respond <strong>to</strong> such pro<strong>to</strong>cols also<br />
with a fast rise <strong>in</strong> <strong>body</strong> <strong>temperature</strong>. This phenomenon can<br />
be considered as a genu<strong>in</strong>e bemotionalQ fever, because it can<br />
be blocked by salicylate <strong>and</strong> is usually associated with<br />
tachycardia [2,3]. A rise <strong>in</strong> <strong>body</strong> <strong>temperature</strong> is recognised<br />
* Correspond<strong>in</strong>g author. Center for Cellular <strong>and</strong> Molecular Neurobiology,<br />
Behavioural Neuroendocr<strong>in</strong>ology Research Group, University of<br />
Liège, 17 place Delcour (Bat. L1), B-4020 Liège, Belgium. Tel.: +32 4<br />
3665973; fax: +32 4 3665971.<br />
E-mail address: C.Carere@ulg.ac.be (C. Carere).<br />
as a typical component of the emotional <strong>stress</strong> <strong>response</strong> also<br />
<strong>in</strong> rats <strong>and</strong> mice [4–8], as well as <strong>in</strong> other mammals, birds<br />
<strong>and</strong> reptiles [3,9–13].<br />
In birds, <strong>body</strong> <strong>temperature</strong> has been ma<strong>in</strong>ly studied <strong>in</strong> the<br />
framework of the energetic of endotherms. Overall, it is<br />
higher than <strong>in</strong> mammals, it decreases with <strong>in</strong>creas<strong>in</strong>g <strong>body</strong><br />
mass, <strong>and</strong> is affected by rest<strong>in</strong>g phase, circannual variations<br />
<strong>and</strong> sex, females exhibit<strong>in</strong>g slightly higher values than<br />
males [14].<br />
Breath <strong>rate</strong>, the frequency of respira<strong>to</strong>ry acts, is a<br />
parameter for which much less <strong>in</strong>formation is available <strong>in</strong><br />
birds. Breath<strong>in</strong>g frequency could respond <strong>to</strong> fearful stimuli<br />
or emotions similarly <strong>to</strong> cardiovascular parameters, such as<br />
heart <strong>rate</strong>, because both are controlled, at least <strong>in</strong> part, by the<br />
au<strong>to</strong>nomic nervous system. Follow<strong>in</strong>g h<strong>and</strong>l<strong>in</strong>g, eider ducks<br />
(Somateria mollissima) displayed a tachycardia for 2–3 m<strong>in</strong><br />
without any visible mo<strong>to</strong>r <strong>response</strong> [3]. Such parameters are<br />
0031-9384/$ - see front matter D 2004 Elsevier Inc. All rights reserved.<br />
doi:10.1016/j.physbeh.2004.07.009
906<br />
C. Carere, K. van Oers / Physiology & Behavior 82 (2004) 905–912<br />
<strong>in</strong>dex of the emotional <strong>and</strong> <strong>stress</strong> <strong>response</strong> [8], but are<br />
difficult <strong>to</strong> obta<strong>in</strong> <strong>in</strong> a small songbird. Recently, <strong>breath</strong> <strong>rate</strong><br />
has been counted <strong>in</strong> great tits about 18 h follow<strong>in</strong>g social<br />
defeat (Parus major), but no effect was detected, probably<br />
because an <strong>in</strong>creased activity of the adrenergic system<br />
occurs only <strong>in</strong> the very short term follow<strong>in</strong>g exposure <strong>to</strong> a<br />
<strong>stress</strong>ful stimulus [12].<br />
Individuals differ nonr<strong>and</strong>omly <strong>in</strong> the way they deal with<br />
<strong>stress</strong>ors <strong>and</strong> novelties <strong>and</strong> appear <strong>to</strong> vary along a<br />
behavioural cont<strong>in</strong>uum from shy <strong>to</strong> bold [15–17]. These<br />
differences covary with other behavioural traits, such as<br />
aggression, exploration, risk tak<strong>in</strong>g, fearfulness <strong>and</strong> reactivity:<br />
for example, bold <strong>and</strong> less fearful <strong>in</strong>dividuals are<br />
more aggressive than shy <strong>and</strong> fearful <strong>in</strong>dividuals [18–24].<br />
Several l<strong>in</strong>es of evidence, <strong>in</strong>clud<strong>in</strong>g selection l<strong>in</strong>es experiments,<br />
suggest that these differences are aspects of a<br />
coherent <strong>and</strong> heritable behavioural organization ma<strong>in</strong>ta<strong>in</strong>ed<br />
by natural selection [21–25]. Such <strong>in</strong>dividual behavioural<br />
organizations are referred <strong>to</strong> as behavioural syndromes,<br />
predispositions, profiles, cop<strong>in</strong>g styles, st<strong>rate</strong>gies, <strong>and</strong> axes<br />
[26,27], comparable <strong>to</strong> human personalities [28]. In rodents,<br />
proactive personalities (bold, bactiveQ <strong>and</strong> aggressive<br />
animals) are associated with high neurosympathetic activity<br />
<strong>and</strong> low HPA reactivity, whereas reactive personalities (shy,<br />
bpassiveQ <strong>and</strong> less aggressive animals) are associated with<br />
high cardiac parasympathetic activity <strong>and</strong> high HPA<br />
reactivity [21,22,29,30].<br />
In the great tit (P. major), a small passer<strong>in</strong>e bird, many<br />
<strong>in</strong>dividuals show extreme phenotypes with<strong>in</strong> a given<br />
population, be<strong>in</strong>g bfastQ (or bold) or bslowQ (or shy) <strong>in</strong><br />
exploration tasks, <strong>in</strong>clud<strong>in</strong>g novelty <strong>response</strong>s [15]. Recent<br />
studies demonst<strong>rate</strong> the presence of considerable amount of<br />
both additive genetic variation <strong>and</strong> dom<strong>in</strong>ance genetic<br />
variation of such personality traits <strong>in</strong> wild great tit<br />
populations [31] <strong>and</strong> selection l<strong>in</strong>es experiments have<br />
shown high heritability for early explora<strong>to</strong>ry behaviour<br />
based on four generations of artificial selection [23]. These<br />
trait characteristics are relatively stable across age [23].<br />
They correlate both phenotypically <strong>and</strong> genetically with<br />
differences <strong>in</strong> aggression [19,24,32], forag<strong>in</strong>g behaviour<br />
[15,33], <strong>response</strong> <strong>to</strong> social <strong>stress</strong> <strong>and</strong> risk-tak<strong>in</strong>g behaviour<br />
[12,34–36]. Therefore, they may <strong>in</strong>deed reflect personalities<br />
[27,36]. The l<strong>in</strong>es show resemblance <strong>to</strong> selection l<strong>in</strong>es<br />
established from wild house mice populations [18,24,27].<br />
This resemblance <strong>in</strong>cludes also physiological parameters<br />
<strong>in</strong>volved <strong>in</strong> the <strong>stress</strong> <strong>response</strong>: the great tit data on <strong>breath</strong><br />
<strong>rate</strong> <strong>in</strong>dicate a trend for higher levels <strong>in</strong> the l<strong>in</strong>e of slow<br />
<strong>in</strong>dividuals [12], while data on the adrenocortical <strong>response</strong><br />
<strong>in</strong>dicate higher HPA reactivity <strong>in</strong> the same l<strong>in</strong>e [35]. The<br />
great tit l<strong>in</strong>es also resemble two l<strong>in</strong>es of leghorns orig<strong>in</strong>ally<br />
selected for productivity traits, the so-called high feather<br />
peck<strong>in</strong>g frequency (HP) <strong>and</strong> low feather peck<strong>in</strong>g frequency<br />
(LP) l<strong>in</strong>es [27]. Hens of the LP l<strong>in</strong>e, that resemble shy great<br />
tits, had higher basal <strong>and</strong> <strong>stress</strong>-<strong>in</strong>duced (manual restra<strong>in</strong>t)<br />
plasma corticosterone levels than hens of the HP l<strong>in</strong>e, that<br />
resemble the bold great tits [37,38]. Hens of the LP l<strong>in</strong>e also<br />
showed higher parasympathetic <strong>response</strong> than birds of the<br />
high feather peck<strong>in</strong>g l<strong>in</strong>e [39].<br />
This study was designed <strong>to</strong> test how great tits different<br />
for shyness <strong>and</strong> boldness respond physiologically (<strong>body</strong><br />
<strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong>) <strong>to</strong> an unpredictable <strong>and</strong> acute<br />
<strong>stress</strong>ful event (capture <strong>and</strong> h<strong>and</strong>l<strong>in</strong>g). We tested two<br />
<strong>in</strong>dependent groups, one dur<strong>in</strong>g daytime (active phase)<br />
<strong>and</strong> one dur<strong>in</strong>g nighttime (<strong>in</strong>active phase). The nighttime<br />
group was tested primarily <strong>in</strong> an attempt <strong>to</strong> record m<strong>in</strong>imum<br />
rest<strong>in</strong>g levels. We hypothesised that shy <strong>in</strong>dividuals show<br />
higher or more prolonged <strong>response</strong>s than bold <strong>in</strong>dividuals <strong>in</strong><br />
both parameters [10,12,21,30,39].<br />
2. Methods<br />
2.1. Subjects <strong>and</strong> hous<strong>in</strong>g<br />
The great tit is a terri<strong>to</strong>rial, nonmigra<strong>to</strong>ry passer<strong>in</strong>e bird<br />
(<strong>body</strong> mass: 16–20 g) <strong>in</strong>habit<strong>in</strong>g woods <strong>and</strong> parks. The<br />
group of birds tested dur<strong>in</strong>g the active phase consisted<br />
orig<strong>in</strong>ally of 90 chicks collected from a wild population at<br />
the age of 10 days <strong>in</strong> May–June <strong>and</strong> h<strong>and</strong> reared under<br />
st<strong>and</strong>ard conditions until <strong>in</strong>dependence [15]. From <strong>in</strong>dependence<br />
onwards (days 25–30 after hatch<strong>in</strong>g), birds were<br />
housed <strong>in</strong>dividually <strong>in</strong> st<strong>and</strong>ard cages of 0.90.40.5 m<br />
with a wooden bot<strong>to</strong>m, <strong>to</strong>p, sides <strong>and</strong> rear walls, a wiremesh<br />
front <strong>and</strong> three perches. They were kept under natural<br />
light conditions (LD 10:14 h dur<strong>in</strong>g the period of the <strong>stress</strong><br />
pro<strong>to</strong>col, December 1998), <strong>and</strong> had audi<strong>to</strong>ry <strong>and</strong> visual<br />
contact with other <strong>in</strong>dividuals housed <strong>in</strong> the same room.<br />
Food (commercial seed mixture, sunflowers <strong>and</strong> a prote<strong>in</strong><br />
rich mixture supplemented daily with mealworms, Tenebrio<br />
moli<strong>to</strong>r) <strong>and</strong> water were provided ad libitum.<br />
The birds tested dur<strong>in</strong>g the <strong>in</strong>active phase were 16 adult<br />
male great tits (2–3 years old) orig<strong>in</strong>at<strong>in</strong>g from a program of<br />
bidirectional artificial selection started <strong>in</strong> 1993 on the basis<br />
of the outcome of exploration tests carried out at the age of<br />
30–40 days [23]. L<strong>in</strong>es did not differ <strong>in</strong> <strong>body</strong> mass or tarsus<br />
length. The birds belonged <strong>to</strong> the third <strong>and</strong> fourth<br />
generation, 6 of the Slow (shy) <strong>and</strong> 10 of the Fast (bold)<br />
l<strong>in</strong>e. They were housed <strong>and</strong> ma<strong>in</strong>ta<strong>in</strong>ed as described above.<br />
Birds were sexed with molecular markers [40]. Body<br />
mass <strong>and</strong> other morphometric measurements were taken<br />
about 2 weeks before the <strong>stress</strong> pro<strong>to</strong>col.<br />
2.2. Novel object tests<br />
Two tests were carried out at the age of 35–40 days after<br />
hatch<strong>in</strong>g, <strong>in</strong>troduc<strong>in</strong>g a novel object on one of the outer<br />
perches. A penlight battery was used on the first day <strong>and</strong> an<br />
8-cm p<strong>in</strong>k rubber <strong>to</strong>y on the second day. Birds were<br />
characterized for shyness <strong>and</strong> boldness assess<strong>in</strong>g their<br />
latency <strong>to</strong> approach the object <strong>and</strong> the shortest distance <strong>to</strong><br />
it with<strong>in</strong> 120 s. The results for each test were converted<br />
l<strong>in</strong>early <strong>to</strong> a 0–5 scale. A score of 5 was given when the bird
C. Carere, K. van Oers / Physiology & Behavior 82 (2004) 905–912 907<br />
pecked the object <strong>and</strong> a score of 0 was given when the bird<br />
did not l<strong>and</strong> on the perch with the object [15,23]. The sum<br />
of the test scores, rang<strong>in</strong>g from 0 <strong>to</strong> 10 is the shyness–<br />
boldness trait. We categorised as bshyQ all <strong>in</strong>dividuals with<br />
scores from 0 <strong>to</strong> 3 (<strong>in</strong>cluded) <strong>and</strong> bboldQ all <strong>in</strong>dividuals with<br />
scores from 6 (<strong>in</strong>cluded) <strong>to</strong> 10. Twenty-n<strong>in</strong>e birds match<strong>in</strong>g<br />
these criteria were selected for the experiment (14 bboldQ,15<br />
bshyQ <strong>in</strong>dividuals; mean scoreFS.E.M.=7.3F0.4 <strong>and</strong><br />
0.9F0.3; Mann–Whitney U-test z= 4.7, pb0.001). The<br />
birds of the selection l<strong>in</strong>es were tested <strong>in</strong> the same way <strong>to</strong><br />
check for the l<strong>in</strong>e difference <strong>in</strong> the juvenile phase (fast l<strong>in</strong>e<br />
mean scoreFS.E.M.=7.3F0.5; slow l<strong>in</strong>e=0.0F0.0, z= 3.3,<br />
pb0.01) <strong>and</strong> <strong>in</strong> adulthood (fast l<strong>in</strong>e mean scoreFS.E.M.=<br />
7.8F0.7; slow l<strong>in</strong>e=3.4F1.3; z= 2.35, p=0.02).<br />
2.3. H<strong>and</strong>l<strong>in</strong>g <strong>stress</strong> pro<strong>to</strong>col <strong>and</strong> physiological<br />
measurements<br />
The adult males of the selection l<strong>in</strong>es were tested dur<strong>in</strong>g<br />
the <strong>in</strong>active phase at the end of the dark period, between 0630<br />
<strong>and</strong> 0730 h. The other group of birds was tested dur<strong>in</strong>g the<br />
active phase between 0900 <strong>and</strong> 1200 h. Each bird was tested<br />
accord<strong>in</strong>g <strong>to</strong> the follow<strong>in</strong>g procedure: first, the subject was<br />
chased <strong>in</strong> its home cage <strong>and</strong> the time was measured from the<br />
moment the cage was entered with the right h<strong>and</strong> until the<br />
bird was caught (catch<strong>in</strong>g time). This time scored zero dur<strong>in</strong>g<br />
the <strong>in</strong>active phase, because birds were caught <strong>in</strong> the darkness<br />
<strong>and</strong> care was taken <strong>to</strong> avoid wak<strong>in</strong>g them up. After capture,<br />
one of two physiological parameters, either <strong>body</strong> <strong>temperature</strong><br />
(T1) or <strong>breath</strong> <strong>rate</strong> (B1), was measured immediately; afterwards,<br />
the bird was put <strong>in</strong> a cot<strong>to</strong>n bag hang<strong>in</strong>g apart <strong>and</strong> a<br />
second measurement of the same parameter was taken after 5<br />
m<strong>in</strong> (T2, B2). After the second measurement, the bird was<br />
released <strong>in</strong> its home cage. Sixty m<strong>in</strong>utes later, the same<br />
procedure was used <strong>to</strong> measure the second physiological<br />
parameter. The assignment of which of the two parameters<br />
was measured first was r<strong>and</strong>om. In the birds tested dur<strong>in</strong>g the<br />
<strong>in</strong>active phase, <strong>breath</strong> <strong>rate</strong> was measured immediately after<br />
(i.e., few seconds) <strong>body</strong> <strong>temperature</strong>.<br />
Body <strong>temperature</strong> was measured with a thermometric<br />
probe (AMR Therm—30+100 NTC TYP C 2244-1,<br />
AHLBORN Mess-und Regelungstechnik D-8150 HOLZ-<br />
KIRCHEN—P.O.B 12 60, Germany) constantly kept <strong>in</strong><br />
warm water (30–35 8C). The probe was <strong>in</strong>serted <strong>in</strong> the<br />
cloaca for 10 mm. It <strong>to</strong>ok approximately 5–10 s, until the<br />
value on the display became stable. Breath <strong>rate</strong> was<br />
obta<strong>in</strong>ed by count<strong>in</strong>g the breast movements dur<strong>in</strong>g 60 s<br />
while firmly keep<strong>in</strong>g the bird <strong>in</strong> the h<strong>and</strong>. Body mass was<br />
measured with an electronic balance <strong>to</strong> the nearest 0.1 g<br />
<strong>and</strong> tarsus with slid<strong>in</strong>g calipers <strong>to</strong> the nearest 0.1 mm 2<br />
weeks before the tests.<br />
2.4. Data analysis<br />
Correlational analysis (Spearman correlation coefficient)<br />
was used <strong>to</strong> explore the association between catch<strong>in</strong>g time,<br />
<strong>body</strong> mass, <strong>body</strong> <strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong>. To test if sex<br />
or type affected catch<strong>in</strong>g time, univariate analysis of<br />
variance with the two variables as fixed fac<strong>to</strong>rs <strong>in</strong>clud<strong>in</strong>g<br />
their <strong>in</strong>teraction was run with <strong>body</strong> <strong>temperature</strong> or <strong>breath</strong><br />
<strong>rate</strong> as dependent variables. A similar analysis was run <strong>to</strong><br />
check the effect of sex <strong>and</strong> type on <strong>body</strong> mass. For the<br />
analysis of the <strong>stress</strong> <strong>response</strong> <strong>in</strong> relation <strong>to</strong> type (shy <strong>and</strong><br />
bold), sex <strong>and</strong> sampl<strong>in</strong>g time (first <strong>and</strong> second measurement),<br />
we used parametric fac<strong>to</strong>rial analysis of variance<br />
consider<strong>in</strong>g type <strong>and</strong> sex as group<strong>in</strong>g fac<strong>to</strong>r <strong>and</strong> sampl<strong>in</strong>g<br />
time as repeated-measure fac<strong>to</strong>r (two levels). Variance was<br />
homogeneous across the four subgroups. Multiple comparisons<br />
for the variable type, sepa<strong>rate</strong>ly for the two sampl<strong>in</strong>g<br />
times, were performed by Tukey–Kramer least significant<br />
difference (LSD) test. The use of this test is recommended<br />
even <strong>in</strong> the absence of significant ma<strong>in</strong> or <strong>in</strong>teraction effects<br />
<strong>in</strong> the analysis of variance [41], because the procedure<br />
protects from the <strong>in</strong>creased probability of type I errors due<br />
<strong>to</strong> the repeated measure. An overall model pool<strong>in</strong>g the two<br />
groups of birds was run <strong>to</strong> test the effect of activity period.<br />
When necessary, data were normalized by log transformation<br />
prior <strong>to</strong> the parametric analyses. All tests were two<br />
tailed. Significance level was a=0.05.<br />
3. Results<br />
3.1. Active phase<br />
Males were significantly heavier than females [means<br />
<strong>and</strong> st<strong>and</strong>ard errors: 19.34F0.23 vs. 18.18F0.17 g, respectively,<br />
F(1,25)=5.7, pb0.004] <strong>and</strong> no effect of type<br />
[ F(1,25)=0.003, p=0.96] or its <strong>in</strong>teraction with sex<br />
[ F(1,25)=1.2, p=0.29] were found. No sex effects were<br />
found <strong>in</strong> the novel object tests [sex, F(1,25)=1.8, p=0.19;<br />
sextype, F(1,25)=1.4, p=0.25].<br />
In the <strong>body</strong> <strong>temperature</strong> session, catch<strong>in</strong>g time ranged<br />
between 4 <strong>and</strong> 55 s (mean: 21.8F14.5 s), but it did not<br />
correlate with any of the two measurements (Table 1), <strong>and</strong><br />
did not differ <strong>in</strong> relation <strong>to</strong> type [ F(1,25)=0.9, p=0.35] or<br />
sex [ F(1,25)=0.41, p=0.53]. Comput<strong>in</strong>g the correlation<br />
Table 1<br />
Association (Spearman correlation coefficient) between the variables<br />
catch<strong>in</strong>g time (CtT: <strong>body</strong> <strong>temperature</strong> session; CtB: <strong>breath</strong> <strong>rate</strong> session),<br />
<strong>body</strong> <strong>temperature</strong> (T1: first measurement; T2: second measurement) <strong>and</strong><br />
<strong>breath</strong> <strong>rate</strong> dur<strong>in</strong>g the active phase (B1: first measurement; B2: second<br />
measurement)<br />
CtT CtB T1 T2 B1<br />
CtB 0.38*<br />
T1 0.16 0.15<br />
T2 0.04 0.20 0.74**<br />
B1 0.32 0.21 0.19 0.24<br />
B2 0.13 0.07 0.11 0.12 0.41*<br />
N=29.<br />
* pb0.05.<br />
** pb0.01.
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sepa<strong>rate</strong>ly for the two l<strong>in</strong>es yielded similar results. In the<br />
<strong>breath</strong> <strong>rate</strong> session, it <strong>to</strong>ok significantly less time <strong>to</strong> catch a<br />
bird than <strong>in</strong> the <strong>body</strong> <strong>temperature</strong> session [ F(1,56)=5.3<br />
pb0.01], values rang<strong>in</strong>g between 4 <strong>and</strong> 40 s (mean:<br />
11.9F9.4 s). Catch<strong>in</strong>g time <strong>in</strong> the <strong>breath</strong> <strong>rate</strong> session did<br />
not differ <strong>in</strong> relation <strong>to</strong> type [ F(1,25)=0.01, p=0.92] or sex<br />
[ F(1,25)=0.05, p=0.82] <strong>and</strong> did not correlate with any of<br />
the two measurements (Table 1). No significant correlation<br />
was found between <strong>body</strong> <strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong> <strong>in</strong> any<br />
of the two measurements, whereas first <strong>and</strong> second<br />
measurements showed a positive correlation <strong>in</strong> both<br />
parameters (Table 1).<br />
Body <strong>temperature</strong> was significantly higher <strong>in</strong> the first<br />
measurement than <strong>in</strong> the second one [sampl<strong>in</strong>g time,<br />
F(1,25)=23.9, pb0.01, Figs. 1a <strong>and</strong> 2a]. No overall effect<br />
of type was evident [ F(1,25)=1.1, p=0.29]. In shy<br />
<strong>in</strong>dividuals, the decrease <strong>in</strong> <strong>body</strong> <strong>temperature</strong> <strong>in</strong> the second<br />
measurement was less marked than <strong>in</strong> bold <strong>in</strong>dividuals<br />
[typesampl<strong>in</strong>g time, F(1,25)=3.7, p=0.06, but pb0.05 <strong>in</strong><br />
Tukey–Kramer LSD test <strong>in</strong> the second measurement, Fig.<br />
1a]. Females had higher <strong>temperature</strong>s than males <strong>in</strong> both<br />
measurements [sex, F(1,25)=7.9, p=0.01, Fig. 2a] by about<br />
Fig. 2. Body <strong>temperature</strong> (a) <strong>and</strong> <strong>breath</strong> <strong>rate</strong> (b) <strong>in</strong> male <strong>and</strong> female great tits<br />
immediately after capture (T1, B1) <strong>and</strong> after 5 m<strong>in</strong> (T2, B2) dur<strong>in</strong>g the<br />
active phase. Values are means+S.E.M. **pb0.01.<br />
Fig. 1. Body <strong>temperature</strong> (a) <strong>and</strong> <strong>breath</strong> <strong>rate</strong> (b) <strong>in</strong> shy <strong>and</strong> bold great tits<br />
immediately after capture (T1, B1) <strong>and</strong> after 5 m<strong>in</strong> (T2, B2) dur<strong>in</strong>g the<br />
<strong>in</strong>active <strong>and</strong> the active phases. Values are means+S.E.M. *pb0.05;<br />
**pb0.01.<br />
0.8 8C. No significant <strong>in</strong>teraction between sex <strong>and</strong> sampl<strong>in</strong>g<br />
time [ F(1,25)=0.01 p=0.97] or between sex <strong>and</strong> type<br />
[ F(1,25)=0.28, p=0.60] emerged.<br />
Breath <strong>rate</strong> was also significantly higher <strong>in</strong> the first<br />
measurement than <strong>in</strong> the second one [ F(1,25)=4.3, pb0.05,<br />
Figs. 1b <strong>and</strong> 2b]. No ma<strong>in</strong> effect or <strong>in</strong>teraction of type with<br />
sampl<strong>in</strong>g time [ F(1,25)=1.1 p=0.31, F(1,25)=0.22, p=0.64,<br />
respectively] was found. Although male birds showed a<br />
more marked decrease <strong>in</strong> the second measurement, neither a<br />
sex difference [ F(1,25)=1.8, p=0.19, pN0.05 <strong>in</strong> Tukey–<br />
Kramer LSD test <strong>in</strong> the second measurement] nor the<br />
<strong>in</strong>teraction between sex <strong>and</strong> sampl<strong>in</strong>g time [ F(1,25)=2.3<br />
p=0.14] was significant (Fig. 2b).<br />
The effect of sex on <strong>body</strong> <strong>temperature</strong> disappeared<br />
[ F(1,24)=1.5, p=0.23] when <strong>body</strong> mass was <strong>in</strong>troduced <strong>in</strong><br />
the model of the analysis of variance as a covariate<br />
[ F(1,24)=2.9, p=0.09], <strong>in</strong>dicat<strong>in</strong>g that <strong>body</strong> mass could<br />
expla<strong>in</strong> the sex difference. In fact, <strong>body</strong> mass showed a<br />
significant negative association with <strong>body</strong> <strong>temperature</strong> <strong>in</strong><br />
both measurements (r s = 0.44, p=0.02; r s = 0.64, pb0.001,<br />
n=29 for first <strong>and</strong> second measurements, not shown), but<br />
not with <strong>breath</strong> <strong>rate</strong> (r s = 0.19, p=0.32; r s =0.15, p=0.43,<br />
n=29 for first <strong>and</strong> second measurements, not shown). When
C. Carere, K. van Oers / Physiology & Behavior 82 (2004) 905–912 909<br />
the association of <strong>body</strong> mass with <strong>body</strong> <strong>temperature</strong> was<br />
tested sepa<strong>rate</strong>ly for the sexes, a significant negative<br />
correlation <strong>in</strong> both measurements was present <strong>in</strong> females<br />
(r s = 0.54, p=0.02; r s = 0.63, p=0.004, n=19 for first <strong>and</strong><br />
second measurements, Fig. 3a), but not <strong>in</strong> males (r s =0.45,<br />
p=0.19; r s = 0.08, p=0.82, n=10, for first <strong>and</strong> second<br />
measurements, Fig. 3b). This latter result was likely due <strong>to</strong><br />
the presence of an outlier show<strong>in</strong>g very low values <strong>in</strong> both<br />
measurements <strong>to</strong>gether with the lower sample size <strong>in</strong> males<br />
(Fig. 3b).<br />
3.2. Inactive phase<br />
Body <strong>temperature</strong> was significantly higher <strong>in</strong> the second<br />
measurement than <strong>in</strong> the first one [sampl<strong>in</strong>g time,<br />
F(1,14)=9.0, pb0.01, Fig. 1a]. No effect of type or its<br />
<strong>in</strong>teraction with sampl<strong>in</strong>g time was evident [ F(1,14)=0.43,<br />
p=0.52; F(1,14)=0.08, p=0.77, respectively]. Breath <strong>rate</strong><br />
did not differ between the two measurements [sampl<strong>in</strong>g<br />
time, F(1,14)=2.4, p=0.14, Fig. 1b]. No ma<strong>in</strong> effect of type<br />
Fig. 3. Body <strong>temperature</strong> as a function of <strong>body</strong> mass <strong>in</strong> females (a) <strong>and</strong><br />
males (b) immediately after capture (T1) <strong>and</strong> after 5 m<strong>in</strong> (T2) dur<strong>in</strong>g the<br />
active phase.<br />
or its <strong>in</strong>teraction with sampl<strong>in</strong>g time was found, but shy<br />
birds tended <strong>to</strong> have higher <strong>breath</strong> <strong>rate</strong> than bold birds [type,<br />
F(1,14)=3.5, p=0.08; typesampl<strong>in</strong>g time, F(1,14)=2.4,<br />
p=0.14, respectively].<br />
Pool<strong>in</strong>g <strong>in</strong> one model the groups tested <strong>in</strong> the two activity<br />
phases revealed a significant effect of activity period <strong>in</strong> both<br />
parameters [ F(1,41)=109.2, pb0.001 for <strong>body</strong> <strong>temperature</strong>;<br />
F(1,41)=10.6, pb0.01 for <strong>breath</strong> <strong>rate</strong>, Fig. 1a <strong>and</strong> b], <strong>and</strong> a<br />
significant <strong>in</strong>teraction with sampl<strong>in</strong>g time for <strong>body</strong> <strong>temperature</strong><br />
only [ F(1,41)=32.9, pb0.001]: overall, values were<br />
higher dur<strong>in</strong>g the active period, <strong>and</strong> for <strong>body</strong> <strong>temperature</strong>,<br />
the patterns were opposite (Fig. 1a). A ma<strong>in</strong> effect of type<br />
was evident for <strong>breath</strong> <strong>rate</strong> [ F(1,41)=4.3, pb0.05, Fig. 1b]:<br />
shy birds displayed higher values than bold birds.<br />
4. Discussion<br />
4.1. Response <strong>to</strong> h<strong>and</strong>l<strong>in</strong>g <strong>stress</strong> <strong>in</strong> the <strong>in</strong>active <strong>and</strong> the<br />
active phase<br />
Dur<strong>in</strong>g the activity phase, catch<strong>in</strong>g <strong>and</strong> h<strong>and</strong>l<strong>in</strong>g has<br />
produced a pattern <strong>in</strong> which both <strong>body</strong> <strong>temperature</strong> <strong>and</strong><br />
<strong>breath</strong> <strong>rate</strong> decreased with time. Values were higher <strong>in</strong> the<br />
first measurement, immediately after capture, than 5 m<strong>in</strong><br />
later, when birds had been kept <strong>in</strong> a bag. Dur<strong>in</strong>g the <strong>in</strong>active<br />
phase, when birds were caught dur<strong>in</strong>g sleep, the pattern was<br />
opposite for <strong>body</strong> <strong>temperature</strong>, with values <strong>in</strong>creas<strong>in</strong>g with<br />
time. No difference between the first <strong>and</strong> second measurements<br />
was found for <strong>breath</strong> <strong>rate</strong>. Both parameters had higher<br />
values dur<strong>in</strong>g the active than dur<strong>in</strong>g the <strong>in</strong>active period. The<br />
comparison between the phases suggests that dur<strong>in</strong>g the<br />
active phase, at least for <strong>body</strong> <strong>temperature</strong>, the first<br />
measurement represents a <strong>stress</strong>-<strong>in</strong>duced rise <strong>and</strong> the<br />
decrease observed after 5 m<strong>in</strong> represents the tendency <strong>to</strong><br />
return <strong>to</strong> normal (activity) levels. It could be that catch<strong>in</strong>g<br />
time dur<strong>in</strong>g the light phase affects more <strong>breath</strong> <strong>rate</strong> than<br />
<strong>body</strong> <strong>temperature</strong>, as suggested by its borderl<strong>in</strong>e significant<br />
correlation with the first measurement. Interest<strong>in</strong>gly, the<br />
association with catch<strong>in</strong>g time was always negative, i.e.,<br />
shorter times correspond<strong>in</strong>g <strong>to</strong> higher <strong>breath</strong> <strong>rate</strong>s, like if a<br />
sudden fearful episode is more effective than the same<br />
<strong>stress</strong>or act<strong>in</strong>g for a more prolonged time (Table 1). The<br />
overall higher <strong>body</strong> <strong>temperature</strong> dur<strong>in</strong>g the active phase is<br />
not surpris<strong>in</strong>g, because the thermostat biological set-po<strong>in</strong>t<br />
oscillates through the nychtemeron [14].<br />
The rise <strong>in</strong> <strong>body</strong> <strong>temperature</strong> <strong>in</strong> the active phase could be<br />
due <strong>to</strong> <strong>stress</strong>-<strong>in</strong>duced hyperthermia, a phenomenon<br />
described <strong>in</strong> other animal species [5–7]. Catch<strong>in</strong>g the bird<br />
<strong>and</strong> measur<strong>in</strong>g cloacal <strong>temperature</strong> acted as a <strong>stress</strong>or <strong>and</strong><br />
elicited a very rapid hyperthermic <strong>response</strong>. In s<strong>in</strong>gly<br />
housed mice, 80% of the maximal hyperthermic <strong>response</strong><br />
can be reached with<strong>in</strong> 5 m<strong>in</strong> from the start of the <strong>stress</strong> [7].<br />
In our case, the mo<strong>to</strong>r load due <strong>to</strong> the <strong>in</strong>creased activity of<br />
the birds attempt<strong>in</strong>g <strong>to</strong> escape from be<strong>in</strong>g captured could<br />
have <strong>in</strong>duced thermogenesis, because the birds first had a
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high <strong>temperature</strong> (hyperthermia) <strong>in</strong> T1 <strong>and</strong> then a lower<br />
value <strong>in</strong> T2, but still had a high <strong>temperature</strong> (emotional<br />
fever). However, no correlation was found between catch<strong>in</strong>g<br />
time <strong>and</strong> <strong>body</strong> <strong>temperature</strong>, but we cannot exclude the fact<br />
that it did enhance it or its rapidity. It must be noted that (i)<br />
it <strong>to</strong>ok less than 15 s <strong>to</strong> catch 14 out of 29 birds, a short time<br />
<strong>to</strong> allow a substantial hyperactivity able <strong>to</strong> produce thermogenesis<br />
<strong>and</strong> (ii) the behaviour of the birds before be<strong>in</strong>g<br />
caught was variable: some birds were try<strong>in</strong>g <strong>to</strong> flee, whereas<br />
others were freez<strong>in</strong>g or rema<strong>in</strong><strong>in</strong>g immobile <strong>in</strong> a corner of<br />
the cage. Unfortunately, we did not record these <strong>in</strong>dividual<br />
<strong>response</strong>s <strong>in</strong> detail, but taken <strong>to</strong>gether, these po<strong>in</strong>ts may<br />
expla<strong>in</strong> the lack of a significant correlation. In eider ducks<br />
h<strong>and</strong>led without chas<strong>in</strong>g, cloacal <strong>temperature</strong> <strong>in</strong>creased<br />
sharply with<strong>in</strong> 4 m<strong>in</strong> [3]. Anticipa<strong>to</strong>ry fear for an aversive<br />
event [7] could also play a role, as it was hypothesised for<br />
farm m<strong>in</strong>ks show<strong>in</strong>g very high values <strong>in</strong> their first<br />
measurements [10].<br />
The <strong>in</strong>crease <strong>in</strong> <strong>body</strong> <strong>temperature</strong> may be also due <strong>to</strong><br />
emotional fever. Emotional fever has been shown <strong>to</strong> occur<br />
<strong>in</strong> birds, as well as <strong>in</strong> reptiles, <strong>in</strong> <strong>response</strong> <strong>to</strong> gentle h<strong>and</strong>l<strong>in</strong>g<br />
<strong>and</strong> manual restra<strong>in</strong>t [4,5]. However, given our design, it is<br />
not possible <strong>to</strong> dist<strong>in</strong>guish between a genu<strong>in</strong>e fever,<br />
bwantedQ by the thermostat <strong>and</strong> characterized by an upward<br />
shift of the set-po<strong>in</strong>t <strong>temperature</strong>, <strong>and</strong> hyperthermia,<br />
characterized by a rise <strong>in</strong> central <strong>temperature</strong> above the<br />
set-po<strong>in</strong>t <strong>temperature</strong> due <strong>to</strong> an <strong>in</strong>crease <strong>in</strong> heat load [4].<br />
The rise <strong>in</strong> <strong>body</strong> <strong>temperature</strong> <strong>in</strong> the <strong>in</strong>active phase could<br />
be due <strong>to</strong> the transition from rest<strong>in</strong>g <strong>to</strong> activity levels rather<br />
than <strong>stress</strong>, because values never reached those of the<br />
second measurement dur<strong>in</strong>g the light phase. The latter are<br />
likely still far from basel<strong>in</strong>e bactivityQ levels. It is expected<br />
that subsequent measurement would lead <strong>to</strong> the same levels.<br />
In birds, the mean day–night difference is 2.48 8C [14].<br />
These data provide the first evidence of a hyperthermic<br />
<strong>and</strong> au<strong>to</strong>nomic <strong>response</strong> <strong>to</strong> h<strong>and</strong>l<strong>in</strong>g <strong>stress</strong> <strong>in</strong> a songbird <strong>and</strong><br />
suggest that <strong>body</strong> <strong>temperature</strong> <strong>and</strong> <strong>breath</strong> <strong>rate</strong> are <strong>in</strong>dica<strong>to</strong>rs<br />
of acute <strong>stress</strong> <strong>in</strong> songbirds. They can be easily measured <strong>in</strong><br />
field <strong>and</strong> labora<strong>to</strong>ry condition <strong>and</strong> should be recorded <strong>in</strong><br />
addition <strong>to</strong> other parameters <strong>in</strong>volv<strong>in</strong>g bleed<strong>in</strong>g, such as<br />
corticosterone plasma levels.<br />
4.2. Sex difference<br />
Females displayed higher values of <strong>body</strong> <strong>temperature</strong><br />
than males <strong>in</strong> both sampl<strong>in</strong>g times <strong>and</strong> a similar trend, but<br />
not significant, was found for <strong>breath</strong> <strong>rate</strong>. This f<strong>in</strong>d<strong>in</strong>g is<br />
unlikely <strong>to</strong> be related <strong>to</strong> the behavioural phenotype, because<br />
no sex differences were found <strong>in</strong> the novel object score<br />
dur<strong>in</strong>g the juvenile phase. It could be either due <strong>to</strong><br />
differential <strong>stress</strong> responsiveness between the sexes, or <strong>to</strong><br />
a sex difference <strong>in</strong> basel<strong>in</strong>e levels.<br />
Sex is thought <strong>to</strong> be a major variable conferr<strong>in</strong>g<br />
differential vulnerability <strong>to</strong> <strong>stress</strong>. Results are, however,<br />
often contrast<strong>in</strong>g <strong>and</strong> likely depend<strong>in</strong>g on the ecology of the<br />
species, as well as on the type of <strong>stress</strong>or used [42–44]. In<br />
birds, males have been shown <strong>to</strong> be more susceptible than<br />
females <strong>in</strong> their HPA responsiveness [1,45]. Sex differences<br />
<strong>in</strong> basal levels of <strong>body</strong> <strong>temperature</strong> <strong>in</strong> the same direction of<br />
ours have been found <strong>in</strong> many species [14]. In great tits,<br />
when daily energy expenditure was measured after <strong>in</strong>jection<br />
of doubly labelled water <strong>in</strong> an experiment test<strong>in</strong>g the costs<br />
of parental effort follow<strong>in</strong>g a clutch size manipulation,<br />
females showed higher values than males regardless of the<br />
treatment [46]. A similar difference <strong>in</strong> energy expenditure<br />
between the sexes was also found <strong>in</strong> other passer<strong>in</strong>e species<br />
[47–49], <strong>and</strong> this may reflect a general pattern.<br />
Overall, the literature survey <strong>in</strong> birds <strong>and</strong> the negative<br />
correlation with <strong>body</strong> mass (Fig. 3), sexually dimorphic <strong>in</strong><br />
great tits, po<strong>in</strong>t <strong>in</strong> the direction that the difference may be<br />
<strong>in</strong>dependent of the <strong>stress</strong> procedure. The sex difference<br />
might simply be a physiological adaptation <strong>to</strong> a sex-specific<br />
difference <strong>in</strong> thermal conductance, which is negatively<br />
correlated with <strong>body</strong> mass <strong>in</strong> homeothermic organisms [50].<br />
However, the magnitude of the sex difference <strong>in</strong> our birds<br />
(0.7 8C <strong>in</strong> T1 <strong>and</strong> 0.8 8C <strong>in</strong> T2) was higher than those<br />
reported <strong>in</strong> the literature (0.3–0.5 8C) [14], suggest<strong>in</strong>g a<br />
<strong>stress</strong>-<strong>in</strong>duced enhancement. Therefore, we hypothesise that<br />
<strong>in</strong> species that are sexually dimorphic <strong>in</strong> <strong>body</strong> mass, the<br />
lighter sex (usually females) might face higher energetic<br />
costs than males follow<strong>in</strong>g <strong>stress</strong>.<br />
4.3. Effect of shyness <strong>and</strong> boldness<br />
It was hypothesised that shy <strong>in</strong>dividuals are more<br />
susceptible <strong>to</strong> h<strong>and</strong>l<strong>in</strong>g <strong>stress</strong> than bold <strong>in</strong>dividuals. In<br />
accordance with this, we found that dur<strong>in</strong>g the active phase<br />
<strong>in</strong> shy <strong>in</strong>dividuals, the decrease <strong>in</strong> <strong>body</strong> <strong>temperature</strong> <strong>in</strong> the<br />
second measurement was significantly less marked than <strong>in</strong><br />
bold <strong>in</strong>dividuals. Different temperament traits predict differential<br />
<strong>stress</strong> responsiveness over time.<br />
In male farm m<strong>in</strong>ks from confident <strong>and</strong> fearful breed<strong>in</strong>g<br />
l<strong>in</strong>es undergo<strong>in</strong>g a repeated capture <strong>stress</strong> pro<strong>to</strong>col, no<br />
significant l<strong>in</strong>e differences <strong>in</strong> the <strong>body</strong> <strong>temperature</strong> <strong>response</strong><br />
were detected after first capture, but dur<strong>in</strong>g immobilisation,<br />
fearful animals <strong>in</strong>creased or ma<strong>in</strong>ta<strong>in</strong>ed their <strong>response</strong><br />
levels, while confident ones decreased them [10]. This<br />
pattern is very similar <strong>to</strong> that observed <strong>in</strong> our great tits<br />
strengthen<strong>in</strong>g the hypothesis that a higher reactivity <strong>to</strong><br />
catch<strong>in</strong>g <strong>and</strong> h<strong>and</strong>l<strong>in</strong>g characterizes shy <strong>and</strong> fearful <strong>in</strong>dividuals.<br />
It is important <strong>to</strong> emphasize that this differential<br />
<strong>response</strong> was found <strong>in</strong> birds taken from a wild population <strong>in</strong><br />
which a consistent variation <strong>in</strong> personality traits has been<br />
recently demonst<strong>rate</strong>d <strong>to</strong>gether with its heritability [51].<br />
From these data, the <strong>body</strong> <strong>temperature</strong> <strong>response</strong> seems <strong>to</strong> be<br />
a sensitive marker of both the short-term <strong>stress</strong> <strong>response</strong> <strong>and</strong><br />
the personality trait.<br />
Assum<strong>in</strong>g a similar <strong>response</strong> as for heart <strong>rate</strong>, shy<br />
<strong>in</strong>dividuals were expected <strong>to</strong> display higher values. We<br />
found that overall shy <strong>in</strong>dividuals exhibited higher <strong>breath</strong><br />
<strong>rate</strong> than bold <strong>in</strong>dividuals, confirm<strong>in</strong>g a previous trend <strong>in</strong><br />
the same species [12]. This expectation came from the fact
C. Carere, K. van Oers / Physiology & Behavior 82 (2004) 905–912 911<br />
that respiration, be<strong>in</strong>g likely under vagal control, can be<br />
considered controlled by the parasympathetic system which<br />
is supposed <strong>to</strong> be the dom<strong>in</strong>at<strong>in</strong>g system <strong>in</strong> shy <strong>and</strong><br />
bpassiveQ animals [21,39].<br />
In rodents, the rise <strong>in</strong> <strong>body</strong> <strong>temperature</strong> is simultaneously<br />
accompanied by <strong>in</strong>creases of plasma corticosterone, while<br />
lipopolysaccaride-<strong>in</strong>duced fever also elevates the amount of<br />
biologically available corticosterone [52,53]. This is <strong>in</strong> l<strong>in</strong>e<br />
with previous f<strong>in</strong>d<strong>in</strong>gs that shy <strong>in</strong>dividuals show higher<br />
<strong>stress</strong>-<strong>in</strong>duced corticosterone levels than bold <strong>in</strong>dividuals<br />
[29,30,35,54]. Further studies, <strong>in</strong>clud<strong>in</strong>g an accu<strong>rate</strong> comparison<br />
between the temporal dynamics of the <strong>body</strong><br />
<strong>temperature</strong> <strong>and</strong> the HPA axis reactivity, are needed <strong>to</strong><br />
explore this possibility <strong>and</strong> <strong>to</strong> further validate <strong>body</strong> <strong>temperature</strong><br />
as a physiological marker of the <strong>stress</strong> <strong>response</strong> <strong>in</strong><br />
birds. On the whole, our data provide evidence for a<br />
physiological difference <strong>in</strong> <strong>in</strong>dividuals show<strong>in</strong>g differences<br />
<strong>in</strong> bpersonalityQ traits <strong>in</strong> birds.<br />
Acknowledgements<br />
CC <strong>and</strong> KvO were supported by NWO grants SLW 805-<br />
33-324p <strong>and</strong> SLW 805-33-323. We thank Ton Groothuis,<br />
Henk Visser, Serge Daan, Irene Tieleman, Simon Verhulst,<br />
Piet Drent, Jaap Koolhaas <strong>and</strong> Arie van Noordwijk for helpful<br />
suggestions <strong>and</strong> discussion. Flavia Chiarotti <strong>and</strong> Luca Salvati<br />
gave statistical advice. We are also g<strong>rate</strong>ful <strong>to</strong> Bart van<br />
Ijmeren for animal caretak<strong>in</strong>g, Christa Mateman for molecular<br />
sex<strong>in</strong>g <strong>and</strong> an anonymous referee for his help <strong>in</strong><br />
improv<strong>in</strong>g the manuscript. The experiments presented here<br />
comply with the bPr<strong>in</strong>ciples of animal careQ, publication No.<br />
86-23, revised 1985 of the National Institute of Health <strong>and</strong><br />
with the current laws of the country <strong>in</strong> which the experiments<br />
were performed. Permission for the physiological measurements<br />
was granted by the legal dDierexperimenten<br />
CommissieT of the KNAW, CTO license no. CTO.98-04/00<br />
<strong>and</strong> CTO.99-02/00 <strong>to</strong> KvO. This is publication number 3394<br />
of the Netherl<strong>and</strong>s Institute of Ecology (NIOO-KNAW),<br />
Heteren, The Netherl<strong>and</strong>s.<br />
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