Biology subjects

Engert, E. R.

Publications and source records attributed to Engert, E. R..

3 recordsLinked to original sources

bioRxiv2026

Repeatable individual variation in body temperature is associated with cold tolerance and exercise-induced hyperthermia in zebra finches

In endotherms, body temperature is regulated by balancing the rates of metabolic heat production and dissipation. Birds and mammals maintain high and relatively constant body temperatures, but there is growing evidence that body temperature and heterothermy vary considerably between individuals of a population. Based on the interdependence of metabolic rate and body temperature, variation in body temperature could be expected to be related to metabolic performance. In this study, we aimed to determine if body temperature is a variable and repeatable trait in captive zebra finches (Taeniopygia guttata) and if body temperature could be related to different metrics of performance. We measured body temperature for 14 days in in caged male zebra finches to assess within- and among-individual variation and repeatability, as well as during measurements of three metabolic traits; basal (BMR), summit cold-induced (Msum) and maximum exercise-induced (MMR) metabolic rate. Median Tb (R = 0.48), and peak Tb (R = 0.53) body temperature were repeatable and positively correlated, suggesting that the birds show consistent differences in body temperature. We found that birds with higher daytime body temperatures showed higher thermoregulatory performance in a cold challenge and had higher body temperature during forced exercise. However, daytime body temperature was not related to MMR or BMR. Our study is one of few that have measured the repeatability of body temperature in birds. Our results show that individuals may have distinct body temperature phenotypes which could be related to metabolic and thermoregulatory performance. However, additional research is needed to disentangle the interrelated effects of metabolic capacity, body temperature, and heat dissipation on performance and how this might change with thermal conditions and activity levels.

physiology↗

bioRxiv2026

Air temperature limits aerobic capacity and scope in active birds

Thermal tolerance limits are an important determinant of species vulnerability to climate change. However, most of our knowledge of thermal tolerance pertains to resting animals, which could yield unrealistic predictions about how air temperature will affect animals when they are active. To gain a better understanding of thermoregulatory contstraints in active birds, we induced zebra finches in captivity to exercise continuously in air temperatures ranging from cool to warm (12- 36 C) while we simultaneously measured their metabolic rate, body temperature, and evaporative water loss. During activity, birds overheated in air temperatures well below their resting thermal tolerance limit, and aerobic scope was reduced by 22% at the warmest temperature. Although zebra finches showed a 8-fold increase in evaporative water loss during exercise in the warmest temperature, this was not sufficiently high to compensate for the substantial increase in heat produced during activity. This could explain why birds became hyperthermic and showed reductions in metabolic rate in the higher air temperatures. Thus, our results provide a mechanistic explanation for how heat could limit aerobic capacity and scope in active birds. These findings support growing evidence that increased air temperature can lead to sub-lethal fitness costs in free-living birds.

ecology↗

bioRxiv2023

Using metabolic data to uncover the ontogeny of endothermy in an altricial bird

Altricial songbirds transform themselves from naked poikilotherms to fully-feathered endothermic homeotherms over a matter of weeks from hatching to fledging. The timing of development of endothermy has been studied in altricial birds for over half a century. However, the potential determinants, constraints, and flexibility of the onset of endothermy are not yet fully understood. We experimentally investigated whether brood size influences the ontogeny of endothermic heat production in 4-8 day-old nestling blue tits (Cyanistes caeruleus) in southern Sweden. We found that both nestlings capacity to produce heat and the proportion of nestlings exhibiting a metabolic response to a cooling challenge (15 {degrees}C for 15 min) increased with age. However, we did not find an effect of brood size on the ontogeny of endothermy and this may be explained by the lack of differences in body mass of nestlings in enlarged and reduced broods in our study. The metabolic response in all age groups was brief and not sufficient to sustain a stable body temperature. Our study shows that the development and use of endothermy is present at an early age in nestling blue tits, but further study is needed to disentangle the factors contributing to individual variation in the timing of these developments. This will serve to improve our understanding of a developmental milestone of cold tolerance in birds in the temperate zone that not only face warmer average temperatures, but also increasingly frequent cold snaps and extreme weather. Summary StatementThis study serves to improve our understanding of the ontogeny of endothermy in altricial birds while examining the potential role of brood size in the timing thereof.

ecology↗