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Metabolic responses of shorebird chicks to cold stress: hysteresis of cooling and warming phases

Robert E. Ricklefs1,* and Joseph B. Williams2

1 Department of Biology, University of Missouri-St Louis, 8001 Natural Bridge Road, St Louis, MO 63121-4499, USA
2 Department of Zoology, Ohio State University, 1735 Neil Ave, Columbus, OH 43210, USA



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  		Fig. 1. Body temperature and oxygen consumption of a 5-day-old dunlin Calidris alpina chick through a 2 h down–up (DU) protocol. Ambient temperature was initially close to 30°C and was decreased to approx. 7°C; body temperature decreased to a low of 29.7°C.

 


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  		Fig. 2. Outcome of the down–up (DU) protocol in Fig. 1 portrayed as ln(O2) versus body temperature Tb (A) and the value of ln(O2) adjusted for the Q10 effect versus Tb (B). Data representing Phase I (cooling) are indicated by downward pointing triangles, Phase II (maximum metabolism) by filled circles, and Phase III (warming) by upward pointing triangles. The regression of ln(O2) versus Tb through Phase II has a slope of 0.0732. On the adjusted ln(O2) axis in B, this relationship is horizontal (broken line).

 


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  		Fig. 3. Adjusted ln(O2) from Fig. 2 plotted as a function of body temperature Tb (A), the gradient between body and ambient temperature {Delta}T (Tb-Ta) (B), and rate of change in body temperature {Delta}Tb (C). Symbols distinguishing the phases of the down–up DU protocol are as in Fig. 2.

 


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  		Fig. 4. Results of a down–up (DU) protocol for a 7-day-old lesser yellowlegs Tringa flavipes chick, showing rate of oxygen consumption O2 versus body temperature Tb on a log scale (A) and ln[O2(adj)] as a function of Tb (B), the temperature gradient {Delta}T (Tb-Ta) (C) and the rate of change in Tb ({Delta}Tb) (D). The slope of ln(O2) versus Tb was 0.0274, corresponding to a Q10 of 1.32.

 


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  		Fig. 5. Results of down–up (DU) and cold challenge (CC) protocols for 5-day-old short-billed dowitcher Limnodromus griseus chicks. (A) The full DU protocol, as in Fig. 2A. The DU and CC metabolic rates for Phase I are compared with respect to time (B), body temperature Tb (C) and the temperature gradient {Delta}T (Tb-Ta) (D). The slope of ln(O2) versus Tb for Phase II in A is 0.0828±0.0019, which corresponds to a Q10 of 2.29.

 


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  		Fig. 6. Results of a slow cooling protocol for an 8-day-old lesser yellowlegs Tringa flavipes chick (black symbols) compared to down–up (DU) protocols for two 7-day-old lesser yellowlegs chicks (open and grey symbols). Rate of oxygen consumption O2 is plotted on a logarithmic scale as a function of body temperature Tb (A) and the temperature gradient {Delta}T (B).

 


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  		Fig. 7. Results of the cold plunge protocol for a 3-day-old dunlin Calidris alpina chick (filled symbols) compared with a down–up (DU) protocol for a dunlin chick of the same age (open symbols). Oxygen consumption O2 on a logarithmic scale is plotted as a function of body temperature Tb (A) and the temperature gradient {Delta}T (Tb-Ta) (B) during Phase I.

 


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  		Fig. 8. Results of endurance trials for two 1-day-old Hudsonian godwit Limosa haemastica chicks. (A) Chick 9, 23.0 g; (B) chick 14, 26.4 g. Chamber (broken line) and body (solid line) temperatures and log(rate of oxygen consumption) (filled symbols) are plotted as a function of time during the trial.

 

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© The Company of Biologists Ltd 2003