First published online October 7, 2004
Journal of Experimental Biology 207, 3959-3968 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01233
Comparison of the cost of short flights in a nectarivorous and a non-nectarivorous bird
C. Hambly1,*,
B. Pinshow2,
P. Wiersma3,
S. Verhulst3,
S. B. Piertney4,
E. J. Harper5 and
J. R. Speakman1,6
1 Aberdeen Centre for Energy Regulation and Obesity, School of Biological
Sciences, University of Aberdeen, Aberdeen, AB24 2TZ, Scotland, UK
2 Mitrani Department of Desert Ecology, Jacob Blaustein Institute for Desert
Research, Ben Gurion University of the Negev, Sede Boqer Campus, 84990
Midreshet Ben-Gurion, Israel
3 Zoological Laboratory, University of Groningen, PO Box 14, 9750AA Haren,
The Netherlands
4 NERC Molecular Genetics in Ecology Initiative, School of Biological
Sciences, University of Aberdeen, Aberdeen, AB24 2TZ, Scotland, UK
5 The Waltham Centre for Pet Nutrition, Waltham-on-the-Wolds,
Leicestershire, LE14 4RT, England, UK
6 Aberdeen Centre for Energy Regulation and Obesity, Division of Energy
Balance and Obesity, Rowett Research Institute, Bucksburn, Aberdeen, AB21 9BS,
Scotland, UK
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Fig. 1. Typical 13C isotope elimination curve from (A) Palestine sunbird
Nectarinia osea and (B) starling Sturnus vulgarus. There was
rapid incorporation of the isotope into the body bicarbonate pools and
equilibrum was reached in all cases within 5 min in the sunbirds and 10 min in
the starlings. The isotope was then gradually eliminated over the following 50
min until it approached the pre-measured background level of
13C.
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Fig. 2. Results of the calibration experiment, which examined the relationship
between the isotope elimination rate kc and
 O2 (diamonds,
solid lines) or
CO2 (squares,
broken lines). (A) Sunbirds
O2
(y=5.33x+0.19, r2=0.76) and
CO2
(y=4.38x+0.29, r2=0.80) over a
10–20 min period after injection. In starlings (B)
kc had to be corrected for body bicarbonate pool size
(Nc), before regression against
O2
(y=0.35x+1.11, r2=0.84), and
CO2
(y=0.27x+0.54, r2=0.85), for the time
period 15–30 min after injection.
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Fig. 3. Relationship between the equilibrium enrichment of 0.2 ml of 0.29 mol
l-1 labelled bicarbonate with varying amounts of CO2.
The volumes of CO2 added in moles were log-converted and plotted
against the log-converted enrichment values. The relationship was linear
(r2=0.99) and described by y=1.24x+0.63.
The equation for the relationship was used to calculate the size of the body
bicarbonate pool (Nc) in moles, and subsequently ml of
CO2, given the known equilibrium isotope enrichment in each
bird.
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Fig. 4. Typical example of the raw flight data and the methods used to calculate
kc over the flight period for (A) sunbirds and (B)
starlings. A linear regression was fitted before flight and
forward-extrapolated to the adjusted time when flight began (accounting for
time spent on perches). A polynomial regression was fitted to the enrichment
after flight and back-extrapolated to the adjusted time when the flight ended
(as described by Hambly et al.,
2002 ). The resulting gradient between these two points was the
isotope elimination rate (kc, min-1) over the
flight period.
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Fig. 5. Effects of body mass and flight mode on the flight costs of small birds:
nectarivores (closed symbols) and non-nectarivores (open symbols). The data
were divided into three types of flight: hovering (squares), slow flight
(circles) and fast forward flights (triangles). There were strong significant
effects of both flight mode and body mass on the costs of flight.
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Fig. 6. (A) Phylogenetic tree used to reconstruct the phylogenetically independent
contrasts of body mass and flight cost. (B) The effects of flight mode
(hovering nectivore, slow flight in both nectivore and non-nectivores, and
fast forward flight in non-nectivores) on the costs of flights relative to the
expectation from body mass with the effects of lack of phylogenetic
independence removed. Flight mode had a large significant effect, with the
costs of slow flight in non-nectivores and hovering in nectarivores exceeidng
the costs of slow flight in nectarivores and fast flight in
non-nectarivores.
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© The Company of Biologists Ltd 2004
