Effect of food restriction on the energy metabolism of the Chinese bulbul (Pycnonotus sinensis)

Abstract

Food resources play an important role in the regulation of animals' physiology and behavior. We investigated the effect of short-term food restriction on metabolic thermogenesis of Chinese bulbuls (Pycnonotus sinensis) by measuring changes in body mass, body fat, basic metabolic rate (BMR), and organ mass of wild-caught Chinese bulbuls from Wenzhou, China. Short-term food restriction induced a significant decrease in body mass and body fat but body mass returned to normal levels soon after food was no longer restricted. Food restriction caused a significant reduction in BMR after 7 days (P<0.05), which returned to normal levels after food restriction ceased. Log total BMR was positively correlated with log body mass (r(2)=0.126, P<0.05). The dry masses of livers and the digestive tract were higher in birds that had been subject to temporary food restriction than in control birds and those subject to continual food restriction (P<0.001 and P<0.05, respectively). There was also significant differences in the dry mass of the lungs (P<0.05), heart (P<0.01), and spleen (P<0.05) in birds subject to short-term food restriction compared to control birds and those subject to continual food restriction. BMR was positively correlated with body and organ (heart, kidney and stomach) mass. These results suggest that the Chinese bulbul adjusts to restricted food availability by utilizing its energy reserves, lowering its BMR and changing the weight of various internal organs so as to balance total energy requirements. These may all be survival strategies that allow birds to cope with unpredictable variation in food abundance.

Keywords: Basic metabolic rate; Energy metabolism; Food restriction; Pycnonotus sinensis.

Figure 1

Relationship between body mass and food availability in the Chinese Bulbul (Pycnonotus sinensis) Arrow indicates end of a 7 day period of temporary food restriction (TFR); *: P<0.05.

Figure 2

Differences in digestive efficiency in Chinese Bulbuls (Pycnonotus sinensis) subject to continuous food limitation for 1, 3, 5 or 7 days and those subject to temporary food limitation for 7 days (TFR) Different letters labeled above each bars indicate significant differences.

Figure 3

Differences in (A) initial body weight (P=0.982), (B) body fat, (C) total BMR and (D) unit BMR between Chinese Bulbuls (Pycnonotus sinensis) subject to either continual food restriction for 1, 3, 5 or 7 days and those subject to temporary food limitation for 7 days (TFR) Different letters labeled above each bars indicate significant differences.

Figure 4

Relationship between log BMR and log body mass in Chinese Bulbuls (Pycnonotus sinensis) subject to either continual food restriction for 1, 3, 5 or 7 days or temporary food limitation for 7 days (TFR) Log total BMR was positively correlated with log body mass (r²=0.126, P<0.05, Figure 4).