Temperature and other environmental factors play an integral role in the metabolic adjustments of animals and drive a series of morphological, physiological, and behavioral adaptions essential to survival. However, it is not clear how the capacity of an organism for temperature acclimation translates into seasonal acclimatization to maintain survival. Basal metabolic rate (BMR), evaporative water loss (EWL), and energy budget were measured in the Chinese Hwamei (Garrulax canorus) following winter and summer acclimatization, and in those acclimatized to 15 ​℃ (cold) and 35 ​℃ (warm) under laboratory conditions for 28 days. In addition to the above indicators, internal organ masses, as well as state 4 respiration and cytochrome c oxidase (COX) activity were also measured for the liver, skeletal muscle, heart, and kidney. Both winter-acclimatized and cold-acclimated birds exhibited significantly higher BMR, EWL, and energy budget, as well as organ masses, state 4 respiration, and COX activity compared with the summer-acclimatized and warm-acclimated birds. This indicated that the Chinese Hwamei could adapt to seasonal or just temperature changes through some physiological and biochemical thermogenic adjustments, which would be beneficial to cope with natural environmental changes. A general linear model showed that body mass, BMR, GEI, state 4 respiration in the liver and kidney, and COX activity in the skeletal muscle, liver, and kidney were significantly affected by temperature and acclimation. A positive correlation was observed between BMR and each of the other parameters (body mass, EWL, energy budget, heart dry mass, kidney dry mass, state 4 respiration) in the muscle, heart, and kidney and also between BMR and COX activity in the muscle and kidney. The results suggested that similar to seasonal acclimatization, Chinese Hwameis subjected to temperature acclimation also exhibited significant differences in metabolism-related physiological and biochemical parameters, depending on the temperature. The data also supported the prediction that metabolic adjustment might be the primary means by which small birds meet the energetic challenges triggered by cold conditions.

Extreme hot weather is occurring more frequently due to global warming, posing a significant threat to species survival. Birds in particular are more likely to overheat in hot weather because they have a higher body temperature. This study used a heat stress model to investigate the antioxidant defense mechanisms and changes in fatty acid catabolism in Red-billed Leiothrix (Leiothrix lutea) to gain an understanding of how birds adapt to high temperatures. The birds were divided into five groups: a control group (30 ℃ for 0 days), 1 D group (40 ℃ for 1 day), 3 D group (40 ℃ for 3 days), 14 D group (40 ℃ for 14 days) and recovery group (40 ℃ for 14 days, then 30 ℃ for 14 days). Our results indicated that when Red-billed Leiothrix are subjected to heat stress, malondialdehyde (MDA) content in the liver significantly increased, as did the enzyme activities of catalase (CAT), glutathione–SH–peroxidase (GSH-PX) and total antioxidant capacity (T-AOC) in the liver. Furthermore, there was a significant increase in heat shock protein 70 (HSP₇₀) expression in the liver, while avian uncoupling protein (avUCP) expression in muscle was significantly reduced. Additionally, there was a significant reduction in fatty acid catabolism enzyme activity such as 3-hydroxyacyl-CoAdehydrogenase (HOAD) activity in the heart, and carnitine palmitoyl transferase 1 (CPT-1) and citrate synthase (CS) activity in the heart and liver. Furthermore, fatty acid translocase (FAT/CD₃₆) in the heart, heart-type fatty acid binding protein (H-FABP) and fatty acid binding protein (FABP-pm) in the liver and heart were also significantly decreased. These changes reverted after treatment, but not to the same level as the control group. Our results indicated that when Red-billed Leiothrix are exposed to heat stress their internal antioxidant defense system is activated to counteract the damage caused by high temperatures. However, even with high antioxidant levels, prolonged high temperature exposure still caused some degree of oxidative damage possibly requiring a longer recovery time. Additionally, Red-billed Leiothrix may be able to resist heat stress by reducing fatty acid transport and catabolism.