First published online February 15, 2006
Journal of Experimental Biology 209, 845-859 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02064
The effects of depth, temperature and food ingestion on the foraging energetics of a diving endotherm, the double-crested cormorant (Phalacrocorax auritus)
Manfred R. Enstipp1,*,
David Grémillet1 and
David R. Jones2
1 Centre d'Ecologie et Physiologie Energétiques, CNRS, 23 Rue
Becquerel, F-67087 Strasbourg Cedex 2, France
2 Department of Zoology, University of British Columbia, 6270 University
Boulevard, Vancouver, British Columbia, Canada V6T 1Z4
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Fig. 1. Side view and dimensions of the shallow (A) and deep (B) dive tanks and the
respirometry set-up in the laboratory hut. `F' indicates the feeding spot,
where birds picked up chopped herring pieces. The approximate underwater
routes taken by the birds are indicated by arrows, with arrowheads indicating
the direction of locomotion.
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Fig. 2. Oxygen consumption rates (ml O2 min–1
kg–1) of double-crested cormorants during various activities
at different temperatures (`warm' and `cold') and feeding status
(`post-absorptive' and `absorptive'). Mean temperatures when resting in air
were 22.1 and 8.6°C for `warm' and `cold' trials, respectively. For
temperature values during all other trials, see
Table 1. Oxygen consumption
during resting in air (`warm') was taken as basal metabolic rate. Values are
grand means ± 1 s.d., which were established from individual bird
means. Values above the columns indicate the number of birds used.
*Significantly different from resting (air) values.
 Significantly different from respective `warm' temperature
values.
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Fig. 3. Energy expenditures (W kg–1) of double-crested cormorants
during various activities in relation to temperature (post-absorptive trials
only). Temperature refers to air temperature in the case of `resting in air'
and to water temperature in all other cases. See
Table 2 for details about the
regression equations and the number of trials and birds used for each
category.
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Fig. 4. (A) Stroke frequencies (strokes s–1) during deep and
shallow diving in double-crested cormorants. Values are grand means
established from individual bird means ± 1 s.d. (the number of birds
used is indicated above each column) and are based on 10 observations per bird
and category. Birds ascended passively during deep diving. *Significantly
different from shallow diving. (B) Modelled changes in mechanical work against
buoyancy per s during descent for a 2.1 kg double-crested cormorant (assuming
a vertical descent speed of 1 m s–1). The horizontal line
indicates the point of neutral buoyancy. Note that change is greatest within
the first 10 m.
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Fig. 5. Stomach temperatures (°C) of double-crested cormorants during rest at
night and during the day, during resting in `warm' and `cold' water
(triangles) and during shallow diving in `cold' water (open circles; values
are grand means ± 1 s.d.; N=9 birds). `Day (avg)' is the mean
stomach temperature during the hours of daylight (from sunrise to sunset),
which includes periods of food ingestion. Air temperatures ranged from 10 to
26°C during the day and 0–11°C during the night. All temperature
values were significantly different from the `day rest' value. *Significantly
different from `resting in water' values.
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Fig. 6. Thermal conductance (W m–2 °C–1) of
double-crested cormorants at various air and water temperatures during deep
and shallow diving, when resting in water and when resting in air
(post-absorptive trials only). Temperature refers to air temperature in the
case of `resting in air' and to water temperature in all other cases. See
Table 2 for details about the
number of trials and birds used for each category. Deep diving:
r2=0.56, P<0.001; shallow diving:
r2=0.68, P<0.001; resting in water:
r2=0.61, P<0.06; resting in air:
r2=0.54, P<0.001.
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Fig. 7. Energy expenditure (W) of foot-propelled (open symbols) and wing-propelled
(filled symbols) aquatic birds during diving. The relationship is best
described by the following power function (two variables): energy
expenditure=20.36Mb0.64, where energy
expenditure is in W and Mb is body mass in kg;
r2=0.87. Note that values are plotted along a
log10 scale. The dotted lines indicate the 95% confidence interval.
Values are based on table 1 (from Enstipp
et al., 2005 ) and include only respirometry studies. With the
exception of two values for A. fuligula
(De Leeuw, 1996) and the
values for U. lomvia and U. aalge
(Croll and McLaren, 1993), all
values are based on studies of birds diving in shallow tanks (for references,
see Enstipp et al., 2005).
Values for the three cormorant species were recalculated for a water
temperature of 12.6°C [the water temperature for P. carbo
sinensis (Pcs) in Schmid et
al., 1995] by using established regression equations [P.
aristotelis (Par) (Enstipp
et al., 2005); P. auritus (Pau) (present study);
P. carbo carbo (Pcc) (data from
Grémillet et al.,
2001)].
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© The Company of Biologists Ltd 2006
