Altitudinal variation in parental energy expenditure by white-crowned sparrows

Abstract

SUMMARY We used the doubly labeled water technique to measure daily energy expenditure (DEE) during the incubation and feeding nestling stages in two populations of white-crowned sparrows (Zonotrichia leucophrys)— one montane and migratory, the other coastal and sedentary —that differ in thermal environment and clutch size. We assessed the birds'thermal environment by continuously monitoring (among other variables)operative temperature and wind speed both in the open and within bushes and willow thickets occupied by sparrows. From these measurements, we derived several estimates of the birds' thermal environment, including standard operative temperature (Tes). Shade air temperature and Tes averaged 6.6 and 10.3°C lower, respectively, at the montane study site during DEE measurements. The montane population's DEE averaged 24% higher than that of the sea-level population (103.6±12.2 versus 83.7±9.6 kJ day-1; means ± S.D., N=31 and 22, respectively), reflecting both its larger brood size(3.7 versus 2.9) and the colder environment. The DEE:BMR ratio was lowest in the sea-level population (2.1 versus 2.6), but neither population worked to their physiological capacity to produce young. DEE was significantly correlated with temperature across populations, with Tes explaining 42% of the variation in DEE. Statistically removing the effect of temperature by adjusting DEE to a common temperature reduced the difference in DEE between populations by 34% to 87.7 and 100.8 kJ day-1, respectively, for sea-level and montane populations. Basal and resting metabolic rates were similar in both populations, implying that greater activity in the montane population accounted for its higher temperature-adjusted DEE. Our results indicate that the thermal context within which behavior occurs can significantly affect interindividual variation in DEE. Attempts to assess reproductive effort by measuring DEE should therefore account explicitly for the effect of temperature.

Distinct responses and range shifts of lizard populations across an elevational gradient under climate change

“…Extra‐high‐elevation lizards in our study had higher energy expenditure in all climate scenarios, as shown by higher levels of oxygen consumption. Similarly high energy expenditure also occurs in high‐elevation mammals and birds (Hayes, 1989; Weathers et al, 2002). This kind of high energy expenditure in high elevation animals might be an adaption to extreme environments, leading to a fast pace of life (e.g., fast development and growth, early reproduction, and large reproductive investment) at high elevation (Hille & Cooper, 2015).…”

“…Extra-high-elevation lizards in our study had higher energy expenditure in all climate scenarios, as shown by higher levels of oxygen consumption. Similarly high energy expenditure also occurs in high-elevation mammals and birds (Hayes, 1989;Weathers et al, 2002).…”

Geographic variation in the altitudinal migration patterns, body size, oxidative status and exploratory behavior in a neotropical bird

“…Comparative studies about morphology and physiology of mountain birds show that at high elevations, birds often show large body size (Meiri & Dayan, 2003 ) and down‐regulate their adrenocortical stress response during parental care (Bears et al, 2003 ; Breuner & Hahn, 2003 ; Poblete et al, 2020 ), increases its metabolism (Lindsay et al, 2009 ; Soobramoney et al, 2003 ; Weathers et al, 2002 ), develop a large thermal neutral zone (Martin et al, 1993 ) and show high‐hematocrit values (Borras et al, 2010 ) to cope with elevation and weather extremes. As a result of the increased rate of aerobic metabolism at high elevation, it is also likely that birds produce more reactive oxygen species (ROS), which should be counteracted by an increase in antioxidant levels, because an imbalance in intracellular homeostasis between ROS, and antioxidants can lead to oxidative stress (Metcalfe & Alonso‐Alvarez, 2010 ; Monaghan et al, 2009 ).…”