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First published online March 28, 2008
Journal of Experimental Biology 211, 1326-1335 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.015958
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Body temperature depression and peripheral heat loss accompany the metabolic and ventilatory responses to hypoxia in low and high altitude birds

Graham R. Scott1,*, Viviana Cadena2, Glenn J. Tattersall2 and William K. Milsom1

1 Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
2 Department of Biological Sciences, Brock University, St Catherines, ON, L25 3A1, Canada


Figure 1
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  		Fig. 1. (A) Body temperature (Tb) depression during stepwise hypoxia was less severe in bar-headed geese (light grey triangles) than in greylag geese (black squares) or pekin ducks (dark grey circles). Significant Tb depression began earlier in greylag geese (black arrow) and pekin ducks (dark grey arrow) than in bar-headed geese (light grey dashed arrow), and bar-headed geese reduced Tb less during 7% inspired O2 (asterisk). (B) Tb increased significantly during 20 min of recovery in normoxia in bar-headed geese (light grey dashed arrow) and greylag geese (black arrow) but not in pekin ducks. The body temperature change in each individual was determined by subtracting its pre-hypoxia Tb value (see Results).

 

Figure 2
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  		Fig. 2. Surface temperatures (T) of the bill increased in bar-headed geese (BG, top row), greylag geese (GG, middle row) and pekin ducks (PD, bottom row) during stepwise hypoxia. Inspired O2 was reduced from 21% to 12%, 9%, 7%, and then in bar-headed geese only to 5%. Each level of hypoxia was sustained for 15 min. Scale bar, 10 cm.

 

Figure 3
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  		Fig. 3. (A) Bill surface temperatures increased during stepwise hypoxia in bar-headed geese (light grey triangles), greylag geese (black squares) and pekin ducks (dark grey circles). This increase became significant much earlier in greylag geese (black arrow) and pekin ducks (dark grey arrow) than in bar-headed geese (light grey broken arrow), and was lower in bar-headed geese during 9% inspired O2 (asterisk). (B) Bill temperature decreased after the first minute of normoxic recovery in bar-headed geese (light grey broken arrow) and greylag geese (black arrow) and after the second minute in pekin ducks (dark grey arrow). The bill temperature change in each individual was determined by subtracting its pre-hypoxia value (see Results). Representative thermal images are shown in Fig. 2.

 

Figure 4
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  		Fig. 4. (A) Oxygen consumption rate increased during stepwise hypoxia in bar-headed geese (light grey triangles), greylag geese (black squares) and pekin ducks (dark grey circles). Bar-headed geese had higher oxygen consumption rates than both other species during 7% inspired O2 (asterisks). Differences between species persisted after mean oxygen consumption rates were corrected for differences in body temperature depression (see Materials and methods), using Q10 values of either 2 (short broken lines) or 3 (long broken lines). (B) Oxygen consumption rates decreased rapidly during normoxic recovery in all species.

 

Figure 5
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  		Fig. 5. Total ventilation, breathing frequency, tidal volume and air convection requirements (total ventilation divided by oxygen consumption rate) during stepwise hypoxia (A) and subsequent normoxic recovery (B) in bar-headed geese (light grey triangles), greylag geese (black squares) and pekin ducks (dark grey circles). *Significant difference between bar-headed geese and both greylag geese and pekin ducks.

 

Figure 6
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  		Fig. 6. Body temperature change, oxygen consumption rate and total ventilation during 9% inspired O2 that was sustained for 60 min, followed by 30 min normoxic recovery, in bar-headed geese (light grey triangles) and greylag geese (squares). *Significant difference between bar-headed geese and greylag geese. {dagger}Significant difference from 5 min and 10 min time points (white squares) in greylag geese.

 

Figure 7
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  		Fig. 7. Relationships between arterial oxygen loading and (A) body temperature change, (B) bill temperature change, or (C) oxygen consumption rate during stepwise hypoxia in bar-headed geese (light grey triangles), greylag geese (black squares) and pekin ducks (dark grey circles). Arterial O2 concentration data were measured in our previous study (Scott and Milsom, 2007Go), which used a very similar stepwise hypoxia protocol to the present study. Temperature and O2 consumption data are the values after 15 min at each level of hypoxia. Slopes of linear regressions of body temperature against content were similar between species (bar-headed geese, 0.46±0.08; greylag geese, 0.55±0.03; pekin ducks, 0.56±0.07). Slopes of bill temperature against content were similar between bar-headed geese and pekin ducks (bar-headed geese, –2.5±0.6; greylag geese, –0.80±0.25; pekin ducks, –2.0±0.4). The slope of O2 consumption rate against content was highest in bar-headed geese (–0.68±0.21; significantly higher than greylag geese), followed by pekin ducks (–0.42±0.12), and greylag geese (–0.26±0.04). All regressions were statistically significant.

 

Figure 8
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  		Fig. 8. (A) Bilateral vagotomy did not eliminate body temperature (Tb) depression in response to stepwise hypoxia. Vagotomized ducks exposed to hypoxia (black and white circles) began reducing Tb during 9% inspired O2 (black arrow), and reached lower mean Tb than intact ducks (dark grey circles). (B) Bilateral vagotomy abolished the increase in bill surface temperature that occurs in intact ducks during hypoxia. Vagotomized ducks kept in normoxia for equivalent durations (white circles) did not alter Tb or bill temperature; data for these controls are only shown at the end of each 15 min period for clarity.

 

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© The Company of Biologists Ltd 2008