Partitioning of evaporative water loss in white-winged doves: plasticity in response to short-term thermal acclimation.

Abstract

We investigated changes in the relative contributions of respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) to total evaporative water loss (TEWL) in response to short-term thermal acclimation in western white-winged doves Zenaida asiatica mearnsii. We measured REWL, CEWL, oxygen consumption and carbon dioxide production in a partitioned chamber using flow-through respirometry. In doves housed for 2-4 weeks in a room heated to ca. 43 degrees C during the day, TEWL increased from 5.5+/-1.3 mg g(-1) h(-1) at an air temperature (T(a)) of 35 degrees C to 19.3+/-2.5 mg g(-1) h(-1) at T(a)=45 degrees C. In doves housed at room temperature for the same period, TEWL increased from 4.6+/-1.1 mg g(-1) h(-1) at T(a)=35 degrees C to 16.1+/-4.6 mg g(-1) h(-1) at T(a)=45 degrees C. The CEWL of heat-acclimated doves increased from 3.6+/-1.2 mg g(-1) h(-1) (64% of TEWL) at 35 degrees C to 15.0+/-2.1 mg g(-1) h(-1) (78% of TEWL) at T(a)=45 degrees C. Cool-acclimated doves exhibited more modest increases in CEWL, from 2.7+/-0.7 mg g(-1) h(-1) at T(a)=35 degrees C to 7.8+/-3.4 mg g(-1) h(-1) at T(a)=45 degrees C, with the contribution of CEWL to TEWL averaging 53% over this T(a) range. Cool-acclimated doves became mildly hyperthermic (body temperature T(b)=42.9+/-0.4 degrees C) and expended 35% more energy relative to heat-acclimated doves (T(b)=41.9+/-0.6 degrees C) at T(a)=45 degrees C, even though TEWL in the two groups was similar. In each of the two groups, metabolic rate did not vary with T(a), and averaged 7.1+/-0.5 mW g(-1) in cool-acclimated doves and 6.3+/-0.8 mW g(-1) in heat-acclimated doves. The differences in TEWL partitioning we observed between the two experimental groups resulted from a consistently lower skin water vapour diffusion resistance (r(v)) in the heat-acclimated doves. At T(a)=45 degrees C, r(v) in the cool-acclimated doves was 120+/-81 s cm(-1), whereas r(v) in the heat-acclimated doves was 38+/-8 s cm(-1). Our data reveal that in Z. a. mearnsii, TEWL partitioning varies in response to short-term thermal acclimation.

Full text

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The rates at which terrestrial animals lose water through
evaporation across the skin and respiratory surfaces
have important consequences for their water balance,
thermoregulation and survival. Because of the desiccating
nature of terrestrial environments, adaptation to a terrestrial
existence has required the minimization of evaporative water
losses. In response to these demands, animals have evolved a
number of structures and mechanisms, such as nasal turbinates
and epidermal water-proofing, to moderate rates of evaporation
(Gordon and Olson, 1995). For birds and other endotherms
living in hot environments, however, evaporative water
loss becomes an essential means of heat transfer when
environmental temperatures exceed body temperature
(Dawson and Whittow, 2000). Under these conditions, a
conflict thus arises between the need to conserve water and
maintain an adequate state of hydration, and the requirement
to maintain body temperature below critical limits through
increased evaporative water losses. In this study we focus on
the relative importance of respiratory (REWL) and cutaneous
(CEWL) evaporative water losses to avian thermoregulation
and how they are modified with changing environmental
conditions through time.
Current data provide limited insight into the variation in
REWL and CEWL associated with phylogenetic position,
environmental temperature and acclimation period. In most
avian species investigated to date, CEWL has been found to
represent at least 50% of total evaporative water loss (TEWL)
at moderate air temperatures (Ta) (Bernstein, 1971; Lasiewski
et al., 1971; Dawson, 1982; Webster and Bernstein, 1987;
Webster and King, 1987; Wolf and Walsberg, 1996; Tieleman
and Williams, 2002). Considerably less attention has been
focused on the relative importance of respiratory and cutaneous
evaporative heat loss in response to high air temperatures (Ta
≥35°C). The limited data available on the relative contributions
of CEWL and REWL to TEWL at high Ta values reveal
considerable variation among taxa (Wolf and Walsberg, 1996).
For instance, in the few members of the Columbiformes
(pigeons and doves) examined, CEWL represented more than
203
The Journal of Experimental Biology 207, 203-210
Published by The Company of Biologists 2004
doi:10.1242/jeb.00757
We investigated changes in the relative contributions of
respiratory evaporative water loss (REWL) and cutaneous
evaporative water loss (CEWL) to total evaporative
water loss (TEWL) in response to short-term thermal
acclimation in western white-winged doves Zenaida
asiatica mearnsii. We measured REWL, CEWL, oxygen
consumption and carbon dioxide production in a
partitioned chamber using flow-through respirometry. In
doves housed for 2–4 weeks in a room heated to ca. 43°C
during the day, TEWL increased from 5.5±1.3·mg·g–1·h–1
at an air temperature (Ta) of 35°C to 19.3±2.5·mg·g–1·h–1
at Ta=45°C. In doves housed at room temperature for the
same period, TEWL increased from 4.6±1.1·mg·g–1·h–1at
Ta=35°C to 16.1±4.6·mg·g–1·h–1at Ta=45°C. The CEWL of
heat-acclimated doves increased from 3.6±1.2·mg·g–1·h–1
(64% of TEWL) at 35°C to 15.0±2.1·mg·g–1·h–1(78% of
TEWL) at Ta=45°C. Cool-acclimated doves exhibited
more modest increases in CEWL, from 2.7±0.7·mg·g–1·h–1
at Ta=35°C to 7.8±3.4·mg·g–1·h–1at Ta=45°C, with the
contribution of CEWL to TEWL averaging 53% over
this Ta range. Cool-acclimated doves became mildly
hyperthermic (body temperature Tb=42.9±0.4°C) and
expended 35% more energy relative to heat-acclimated
doves (Tb=41.9±0.6°C) at Ta=45°C, even though TEWL in
the two groups was similar. In each of the two groups,
metabolic rate did not vary with Ta, and averaged
7.1±0.5·mW·g–1
in cool-acclimated
6.3±0.8·mW·g–1in heat-acclimated doves. The differences
in TEWL partitioning we observed between the two
experimental groups resulted from a consistently lower
skin water vapour diffusion resistance (rv) in the heat-
acclimated doves. At Ta=45°C, rv in the cool-acclimated
doves was 120±81·s·cm–1, whereas rv in the heat-
acclimated doves was 38±8·s·cm–1. Our data reveal that in
Z. a. mearnsii, TEWL partitioning varies in response to
short-term thermal acclimation.
doves and
Key words: acclimation, cutaneous evaporative water loss,
respiratory evaporative water loss, water vapour diffusion resistance,
thermoregulation, Zenaida asiatica mearnsii.
Summary
Introduction
Partitioning of evaporative water loss in white-winged doves: plasticity in
response to short-term thermal acclimation
Andrew E. McKechnie* and Blair O. Wolf
UNM Biology Department, MSC03-2020, 1 University of New Mexico, Albuquerque, NM 87131-0001, USA
*Author for correspondence (e-mail: aemckech@unm.edu)
Accepted 16 October 2003

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40% of TEWL at 35°C ≤ Ta ≤ 45°C (Webster and King, 1987;
Withers and Williams, 1990; Hoffman and Walsberg, 1999).
In contrast, in passerine birds the relative contribution of
cutaneous evaporation decreases with increasing Ta (Dawson,
1982; Wolf and Walsberg, 1996; Tieleman and Williams,
2002). In verdins (Auriparus flaviceps: Passeriformes:
Remizidae), for example, the contribution of CEWL decreased
from ca. 60% of TEWL at Ta=35°C to ca. 15% at Ta=50°C
(Wolf and Walsberg, 1996). Tieleman and Williams (2002)
observed similar decreases in the relative contribution of
CEWL with increasing Ta
(Passeriformes: Alaudidae).
An understanding of factors other than taxonomic affiliation
that influence patterns of TEWL partitioning is critical for
understanding avian thermoregulation and water balance at
high environmental temperatures. Of particular interest are
potentially adaptive changes in CEWL in response to
acclimatization, acclimation and/or short-term changes in
evaporative cooling requirements. Tieleman and Williams
(2002) found little evidence for changes in CEWL/TEWL
of larks following thermal acclimation. However, other
researchers have found large changes in the role of cutaneous
evaporation with acclimation. Adult rock doves acclimated to
high Ta values from hatching exhibited elevated rates of CEWL
compared to non-acclimated doves, and dissipated virtually
their entire heat load cutaneously at Ta=60°C (Marder and
Arieli, 1988; Ophir et al., 2002). Evidence that CEWL can be
adjusted over much shorter time scales is provided by Hoffman
and Walsberg (1999), who found that mourning doves
(Zenaida macroura) responded within minutes to experimental
inhibition of REWL by increasing CEWL by 72% at Ta=35°C.
Nevertheless, the periods over which changes in CEWL
associated with thermal acclimation occur remain relatively
unknown.
We investigated the effect of short-term (days to weeks)
thermal acclimation on the partitioning of TEWL in western
white-winged doves (Zenaida asiatica mearnsii). We also
examined the interactions between modes of evaporative water
loss, body temperature, skin temperature and metabolic rate,
in an attempt to provide an integrative view of how heat-
acclimated and non-heat-acclimated doves respond to high
levels of heat stress. We chose white-winged doves for this
study because they winter in southern Mexico under moderate
environmental conditions, but breed during the summer in the
Sonoran Desert of the southwestern United States and
northwestern Mexico, where they frequently experience
environmental temperatures approaching or exceeding 50°C
(B. O. Wolf and A. E. McKechnie, personal observation).
in four species of larks
Materials and methods
Study animals
Fourteen western white-winged doves Zenaida asiatica
mearnsii L. were trapped using mist nets during July 2002 in
the Sand Tanks Mountains on the US Air Force Barry M.
Goldwater Bombing Range (32°49′N; 112°26′W) in southern
Arizona, USA. After capture, the doves were transported by
road to the Department of Biology, University of New Mexico,
Albuquerque, USA. They were housed in an outdoor aviary
with ad libitum access to wild bird seed, grit and drinking water
from mid-July 2002 until late March 2003. Thereafter, they
were transferred indoors, with seven doves housed in each of
two identical rooms (1.8·m long × 1.1·m wide × 2.4·m high).
Each bird occupied a separate cage (0.39·m long × 0.23·m wide
× 0.28·m high) and was provided with food and water ad
libitum. The photoperiod in the rooms (13·h:11·h L:D)
approximately matched the outdoor photoperiod. Air
temperature in each room was measured using a Stowaway
XTI Temperature Logger (Onset Computer Corporation,
Bourne, MA, USA). Beginning 4 days after the doves were
transferred indoors, the day-time air temperature in one of the
rooms (‘hot room’) was elevated to 42.6±0.1°C (mean ± 95%
confidence interval) using three commercially available fan
heaters. The air temperature in the other room (‘cool room’)
and in the hot room at night, averaged 21.7±0.1°C. Hereafter,
we refer to the doves housed in the cool and hot rooms
as ‘cool-acclimated’ and ‘heat-acclimated’, respectively.
Measurements of evaporative water loss were conducted
during an 11-day period in April 2003. The duration of thermal
acclimation to the conditions in the rooms varied from 17–28
days at the time of experiments. The mean body mass of the
doves at the time of the experiments was 142.2±7.4·g and did
not differ among treatment groups.
Measurements of evaporative water loss, O2consumption and
CO2production
We measured the respiratory and cutaneous components
of evaporative water loss in a 14.6·l metabolic chamber,
constructed from 5·mm-thick glass. During measurements, the
bird perched on a stainless steel wire mesh screen placed at a
height that allowed for normal perching postures. Any faeces
produced fell through the mesh into a 2·cm layer of mineral
oil, preventing evaporation. REWL and CEWL were
partitioned using a chamber that was divided into upper (4.3·l)
and lower (10.3·l) compartments by a 1·mm-thick aluminum
partition. A 80·mm×120·mm rectangle was cut from the
partition, and a piece of 0.25·mm-thick stretchable latex
membrane (Semantodontics Dental Dam, Phoenix, AZ, USA)
secured over the opening using an aluminum frame bolted to
the partition. The bird’s head and neck protruded through a
hole punched through the membrane. The diameter of the hole
was slightly less than the diameter of the bird’s neck, and
provided a snug fit. An illustration of a similar chamber may
be found in Wolf and Walsberg (1996). Tieleman and Williams
(2002) suggested that the flow-through mask system they used
to measure REWL and CEWL in four species of lark was an
improvement over the partitioned chamber system used by
previous investigators and in the present study, on the grounds
that cutaneous losses from the head and neck are included in
the respiratory component measured in the upper compartment.
However, this source of error is small and can be minimized
by making corrections to REWL and CEWL measurements
A. E. McKechnie and B. O. Wolf

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Evaporative water loss in doves
based on the surface area of the head and neck that protrude
into the upper chamber (Wolf and Walsberg, 1996; see below).
The experimental air temperature (Ta) was controlled by
placing the metabolism chamber in an insulated 200·l
environmental chamber. The Ta within the environmental
chamber was regulated using a temperature-controlled
circulator (Model 1187, VWR Scientific Products, West
Chester, PA, USA), which pumped fluid through copper
tubing. Air within the environmental chamber was mixed using
a small electric fan. Ta within the metabolism chamber was
measured using a 21-gauge Cu–Cn thermocouple and a TC-
1000 thermocouple meter (Sable Systems, Las Vegas, NV,
USA).
Dry, CO2-free air (dewpoint = –73°C) produced using a FT-
IR Purge Gas Generator (Whatman, Newton, MA, USA)
flowed through the chamber at flow rates of 6–10·l·min–1,
chosen to maintain dewpoints below 1°C in the chamber during
all measurements. Flow rates into the lower compartment of
the chamber were regulated using a FMA-series mass flow
controller (Omega, Bridgeport, NJ, USA), and flow rates into
the upper chamber by a FMA-series mass flow controller and
model 246B mass flow controller (MKS Instruments, Andover,
MA, USA) plumbed in parallel. The mass flow controllers
were calibrated using a 1·l soap bubble flowmeter (Baker and
Pouchot, 1983). Because the partition between the upper and
lower compartments was not completely airtight, we controlled
flow rates to the upper and lower compartments so as to ensure
that no pressure gradient existed between them. During
all measurements, we maintained CO2 concentrations of
<20·p.p.m. in the lower compartment, indicating that leakage
between the compartments was negligible.
Dry, CO2-free control air and excurrent air from the upper
and lower compartments of the metabolism chamber were
sequentially sampled using a TR-RM8 Respirometer
Multiplexer (Sable Systems). The partial pressure of water
vapour and carbon dioxide concentration in sampled air was
measured using a LI-7000 CO2/H2O analyzer (Li-Cor, Lincoln,
NE, USA), calibrated daily using dry, CO2-free air and a span
gas for water vapour generated using a LI-610 portable dew
point generator (Li-Cor) and a certified span gas containing
1020.0·p.p.m. CO2 (Matheson Tri-Gas, Houston, TX, USA).
Dewpoint temperatures of the air samples were well below
those of the ambient environment, ensuring that no
condensation occurred within the sampling system. After the
sample left the LI-7000 CO2/H2O analyzer, water vapour and
CO2 were scrubbed using a Drierite®and Ascarite®column.
The fractional O2 concentration was then determined using a
FC-1B oxygen analyzer (Sable Systems). Output from the
CO2/H2O and oxygen analyzers, and the thermocouple meter,
was digitized using a Universal Interface II (Sable Systems)
and recorded on a personal computer using Datacan V data
acquisition software (Sable Systems), with a sampling interval
of 1·s.
Measurements of skin and body temperature
Body temperature (Tb) was measured by inserting a 36-
gauge Cu–Cn Teflon-coated thermocouple (Physitemp,
Clifton, NJ, USA) approximately 1.5·cm into the cloaca, at
which depth a slight withdrawal did not result in a decrease in
the Tb reading. The thermocouple wire was secured to the
feathers immediately behind the cloaca by a small piece of
adhesive tape. Skin temperature (Tskin) was measured dorsally,
by attaching a similar thermocouple to the skin between the
scapulars using cyanoacrylic adhesive.
Experimental protocol
REWL, CEWL, oxygen consumption (V.
dioxide production (V.
40.0±0.5 and 45.9±0.4°C (means ± 95% confidence intervals).
For convenience, we refer to these experimental Ta values
as 35, 40 and 45°C, respectively. Measurements at each Ta
were carried out during separate 2–3 day periods. At each
experimental Ta, measurements were made in five cool-
acclimated and five heat-acclimated doves, in random order.
All measurements were made in darkness on fed doves, during
the active-phase of their circadian cycle. Typically, each set of
measurements lasted 2·h, and data recorded during the first
30·min of each run were not included in the analyses. In a few
cases, cool-acclimated doves exhibited rapid, apparently
uncontrolled increases in Tbat Ta>45°C, and in such cases we
removed the bird prior to the end of the 2··h period. For each
bird, the interval between each set of measurements was at
least 3 days.
Because REWL and CEWL were measured sequentially,
there was a time lag of 5·min between the respective
measurements. However, 99% equilibrium times for the two
compartments, calculated using the relevant equation in
Lasiewski et al. (1966), were 7–14·min. Since the equilibrium
times (and hence the periods over which gas measurements
were integrated) were greater than the time lag between the
REWL and CEWL measurements, the data are essentially
equivalent to simultaneous measurements. Moreover, we only
used EWL data that were stable during the entire measurement
period.
O∑) and carbon
CO∑) were measured at Ta=34.8±0.5,
Data analysis
We calculated REWL and CEWL from the water vapour
partial pressure in excurrent air from the upper and lower
compartments respectively. We corrected these measurements
for the surface area of the head and neck in the upper
compartment by subtracting a surface-area specific estimate of
CEWL from the head and neck from the measured REWL,
following Wolf and Walsberg (1996). The surface area of the
head and neck in the upper compartment averaged 2.5% of the
total skin surface area, estimated from the equation provided
by Walsberg and King (1978). We calculated whole-body
water vapour diffusion resistance (rv) as rv=(ρ′v(Tskin)–ρva)/
CEWL, where ρ′v(Tskin) is the saturation water vapour density
at skin temperature (g·cm–3), ρva is the water vapour density
of the air in the metabolism chamber (g·cm–3), and CEWL
is surface area-specific cutaneous evaporative water loss
(g·cm–2·s–1) (Webster et al., 1985). Although the effective

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evaporative surface area could conceivably have varied
slightly through postural adjustments, we assumed that it
remained constant during all measurements. We also assumed
that the dorsal Tskin measurements were representative of the
entire skin surface. During the experiments, the water vapour
partial pressure in the chamber varied from 0.097·kPa to
0.616·kPa, corresponding to dewpoints of –22.9°C and 0.1°C.
It is unlikely that these low levels of ambient humidity affected
any properties of the skin that potentially determine rv, such as
the hydration state of surface skin layers.
V.
(1977) and V.
(1995). Respiratory exchange ratios were calculated as
V.
metabolic rates using thermal equivalence data from table·4-2
in Withers (1992). This approach assumes that only
carbohydrates and lipids are metabolized, and a maximum
error of 6% is associated with protein metabolism (Walsberg
and Wolf, 1995).
We subjectively examined all data, and discarded any traces
of gas exchange and/or EWL that were not stable. For each
bird at each Ta, we used the lowest value recorded over 1·min,
representing a mean of 60 measurements. All values are
presented as means ± 95% confidence intervals. We compared
data using t-tests and repeated-measures analyses of variance
(RM-ANOVA; Zar, 1999). Unless otherwise stated, the sample
size for each experimental group was five doves.
O∑ was calculated using the relevant equation in Withers
CO∑ using equation 3 in Walsberg and Wolf
CO∑/V.
O∑ and gas exchange measurements were converted to
Results
Evaporative water loss
The TEWL of cool-acclimated doves increased from
4.6±1.1·mg·g–1·h–1at Ta=35°C to 16.1±4.6·mg·g–1·h–1at
Ta=45°C, and the TEWL of heat-acclimated doves increased
from 5.5±1.3·mg·g–1·h–1at Ta=35°C to 19.3±2.5·mg·g–1·h–1
at Ta=45°C. The TEWL of heat-acclimated doves was
significantly higher than that of cool-acclimated doves at
Ta=40°C (t=4.592; P<0.001), but not at Ta=35°C or 45°C
(Fig.·1A).
The REWL of heat-acclimated doves increased from
1.9±0.2·mg·g–1·h–1at Ta=35°C to 4.3±0.6·mg·g–1·h–1at
Ta=45°C, whereas REWL in cool-acclimated doves increased
from 1.9±0.5·mg·g–1·h–1at Ta=35°C to 8.3±1.9·mg·g–1·h–1at
Ta=45°C (Fig.·1B). REWL did not differ between the two
groups at Ta=35°C or 40°C, but was significantly higher in
cool-acclimated doves at Ta=45°C (t=3.951; P=0.002).
The CEWL of heat-acclimated doves increased from
3.6±1.2·mg·g–1·h–1
(64% of TEWL) at Ta=35°C to
15.0±2.1·mg·g–1·h–1(78% of TEWL) at Ta=45°C, and the
CEWL of cool-acclimated
2.7±0.7·mg·g–1·h–1at Ta=35°C to 7.8±3.4·mg·g–1·h–1at
Ta=45°C. CEWL in heat-acclimated doves was significantly
higher than that of cool-acclimated doves at Ta=40°C (t=6.337;
P<0.001) and at Ta=45°C (t=3.517; P=0.003), but not at
Ta=35°C (Fig.·1C). At Ta=35°C, 40°C and 45°C, the mean
CEWL in heat-acclimated doves was equivalent to 136%,
doves increased from
187% and 192%, respectively, of the corresponding rates
in cool-acclimated doves (Fig.·1C). Surface area-specific
CEWL increased from 1.4±0.4·mg·cm–2·h–1at Ta=35°C to
4.1±1.7·mg·cm–2·h–1at Ta=45°C in the cool-acclimated
doves, and from 1.9±0.6·mg·cm–2·h–1
7.7±1.0·mg·cm–2·h–1at Ta=45°C in the heat-acclimated doves.
The contribution of CEWL to TEWL did not vary
significantly between the three experimental Ta values in cool-
acclimated doves (RM-ANOVA, F2,4=3.119; P=0.100),
although CEWL/TEWL decreased slightly with increasing Ta
(Fig.·2). In contrast, the contribution of CEWL increased
significantly with increasing Ta in the heat-acclimated doves
(RM-ANOVA, F2,4=13.281; P=0.003) from 64±7% of TEWL
at Ta=35°C to 78±2% of TEWL at Ta=45°C (Fig.·2). The
contribution of CEWL to TEWL did not differ between the
cool- and heat-acclimated groups at Ta=35°C (t=1.614;
at Ta=35°C to
A. E. McKechnie and B. O. Wolf
0
5
10
15
20
25
A
0
5
10
15
20
B
32343638404244 4648
0
5
10
15
20
C
Cool-acclimated
Heat-acclimated
Cool-acclimated
Heat-acclimated
Cool-acclimated
Heat-acclimated
Respiratory evaporation
(mg g–1 h–1)
Total evaporation
(mg g–1 h–1)
Cutaneous evaporation
(mg g–1 h–1)
Air temperature (°C)
*
*
*
*
Fig.·1. Mean total evaporative water loss (A), respiratory evaporative
water loss (B) and cutaneous evaporative water loss (C)
(mg·H2O·g–1·body·mass·h–1) as a function of air temperature in cool-
and heat-acclimated western white-winged doves Zenaida asiatica
mearnsii. The error bars represent 95% confidence intervals.
*Significant difference between values (P<0.05).

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Evaporative water loss in doves
P=0.09), but was significantly greater in heat-acclimated doves
at Ta=40°C (t=7.833; P<0.001) and Ta=45°C (t=5.593;
P<0.001; Fig.·2).
Metabolic rate
Metabolic rates did not show significant variation between
the three experimental Ta values in either the cool- (RM-
ANOVA, F2,4=0.480; P=0.636) or heat-acclimated groups
(RM-ANOVA, F2,4=1.139; P=0.367; Fig.·3). The mean
metabolic rate for cool-acclimated doves was 7.1±0.5·mW·g–1,
and the mean metabolic rate for heat-acclimated doves was
6.3±0.8·mW·g–1. At Ta=45°C, the mean metabolic rate of
the cool-acclimated doves was significantly higher (t=2.726;
P=0.013) than that of the heat-acclimated doves (Fig.·3).
Body temperature and skin temperature
Our sample sizes for Tb were in some cases smaller than
those for EWL and metabolic rate because doves sometimes
initially struggled and dislodged the thermocouples shortly
after being placed in the metabolism chamber. The mean Tb of
cool-acclimated doves was significantly higher than that of the
heat-acclimated doves (Table·1) at both Ta=40°C (t=4.314;
P=0.004) and Ta=45°C (t=2.537; P=0.019). This observation
is consistent with the doves’ behavior upon removal from the
metabolic chamber at the termination of the measurements at
Ta=45°C. Whereas heat-acclimated doves showed no
indication of panting or gular flutter, all five cool-acclimated
doves exhibited pronounced panting behavior.
Whole-body water vapour diffusion resistance
In both the heat- and cool-acclimated doves, rv decreased
significantly with increasing Ta(Fig.·4). In the heat-acclimated
doves, mean rv decreased by 78% from 172±78·s·cm–1(N=3)
at Ta=35°C to 38±8·s·cm–1(N=5) at Ta=45°C.
0
20
40
60
80
100
35
40
45
Cool-acclimated
Heat-acclimated
Air temperature (°C)
*
*
Cutaneous contribution to
total evaporation (%)
Fig.·2. The contribution of cutaneous evaporation to total evaporative
water loss at three experimental air temperatures in cool- and heat-
acclimated western white-winged doves Zenaida asiatica mearnsii.
The error bars represent 95% confidence intervals. *Significant
difference between values (P<0.001).
Fig.·3. Mean metabolic rate as a function of air temperature in cool-
and heat-acclimated western white-winged doves Zenaida asiatica
mearnsii. The error bars represent 95% confidence intervals.
*Significant difference between values (P<0.05).
323436384042 444648
0
2
4
6
8
10
Cool-acclimated
Heat-acclimated
Air temperature (°C)
Metabolic rate (mW g–1)
*
Table·1. Cloacal body temperature and dorsal skin
temperature at three air temperatures (Ta) in cool-acclimated
(Cool) and heat-acclimated (Heat) western white-winged
doves Zenaida asiatica mearnsii
Skin
Body temperature (°C)temperature (°C)
Ta(°C)Cool HeatCool Heat
35
40
45
41.9±0.4 (5) 40.4±0.6 (4)
40.8±0.8 (8)
42.6±1.0 (8)
43.0±0.1 (3)
42.9±0.4 (4)
42.3±0.3 (4)
41.9±0.6 (5)
Where no significant differences occurred between cool- and heat-
acclimated doves, pooled values are given.
Values are means ± 95% confidence intervals; N is given in
parentheses.
Fig.·4. Whole-body water vapour diffusion resistance rvas a function
of air temperature in cool- and heat-acclimated western white-
winged doves Zenaida asiatica mearnsii. The solid lines are linear
regressions fitted to the data. The regression for the heat-acclimated
doves (lower line) is rv=536.59–11.01Ta (r2=0.634) and that for the
cool-acclimated doves (upper line) is rv=529.06–9.22Ta (r2=0.395).
The slopes of these regressions did not differ significantly.
32343638
Air temperature (°C)
4042 44464850
0
50
100
150
200
250
300
Cool-acclimated
Heat-acclimated
Whole-body vapour diffusion
resistance (s cm–1)