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First published online October 21, 2005
Journal of Experimental Biology 208, 4091-4098 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01854

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Effects of intake rate on energy expenditure, somatic repair and reproduction of zebra finches

Popko Wiersma^* and Simon Verhulst

Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands

View larger version (15K): [in a new window]   Fig. 1. Foraging time, activity and body mass in relation to chaff/seed ratio. (A) Proportion of time spent foraging between 09:00 h and 10:30 h increased with chaff/seed ratio (F1,77=22.0, P<0.001), decreased with body mass (F1,80=8.81, P<0.005) and with the interaction between temperature and chaff/seed ratio (F1,71=16.2, P<0.001; temperature: F1,70=0.5, P=0.5). The plotted data are not corrected for body mass. (B) Time spent on activities (including foraging) during the observation period was related to temperature (F1,84=39.2, P<0.001) and chaff/seed ratio (F1,84=5.29, P=0.024). (C) Body mass was independent of chaff/seed ratio (GLMM: F1,169=2.23, P=0.14, including individual as random effect).

View larger version (14K): [in a new window]   Fig. 2. Metabolic rate (MR in W) and daily energy expenditure (DEE in kJ) during a 24 h period declined with increasing chaff/seed ratio (F1,85=22.7, P<0.001) and temperature (F1,85=3057, P<0.001), and increased with body mass (F1,93=9.77, P<0.005). The interaction between chaff/seed ratio and ambient temperature was not significant (F1,84=1.41, P=0.24). Also plotted is the metabolizable energy intake as measured by Lemon (1993) in zebra finches on similar chaff/seed regimes. The plotted data are not corrected for body mass.

View larger version (19K): [in a new window]   Fig. 3. Nocturnal and diurnal energy expenditure in relation to chaff/seed ratio and ambient temperature. Nocturnal energy expenditure (kJ 14 h-1) was negatively related to temperature (F1,84=1393, P<0.001) and chaff/seed ratio (F1,84=22.0, P<0.001), and positively to their interaction (F1,84=5.74, P=0.019) and body mass (F1,93=11.8, P<0.001). Diurnal energy expenditure (kJ 10 h-1) was negatively related to chaff/seed ratio (F1,85=15.5, P<0.001) and temperature (F1,85=2265, P<0.001) and positively to body mass (F1,93=5.83, P=0.018), and there was no interaction between temperature and chaff/seed ratio (F1,84=0.13, P=0.72). The plotted data are not corrected for body mass. Values are means ± S.E.M. (N=12).

View larger version (20K): [in a new window]   Fig. 4. Minimum values of metabolic rate (MR) measured during the night. (A) Minimum MR was negatively related to chaff/seed ratio (F1,84=16.1, P<0.001) and temperature (F1,84=1278, P<0.001) and positively to their interaction (F1,84=5.28, P=0.024) and body mass (F1,84=8.69, P<0.005). BMR (values at 32°C; Calder, 1964) was not related to chaff/seed ratio (F1,23=0.26, P=0.62). The plotted data are not corrected for body mass. (B) Minimum values of mass-specific metabolic rates. Mass-specific MR was negatively related to chaff/seed ratio (F1,85=12.9, P<0.001) and temperature (F1,85=1253, P<0.001) and positively with their interaction (F1,85=4.24, P=0.043). Mass-specific BMR was not related to chaff/seed ratio (F1,23=0.02, P=0.89).

View larger version (16K): [in a new window]   Fig. 5. Length of the new outer two tail feathers for birds maintained on different chaff/seed ratios. For P values, see text. Regression equations: female, y=37.28-0.57x (N=12); male, y=35.69-0.32x (N=12).

View larger version (13K): [in a new window]   Fig. 6. Food intake (g bird-1 day-1) on days following the termination of the chaff/seed food regimes (i.e. all birds had seeds without chaff), in relation to the chaff/seed ratio experienced in the previous 6 weeks. Data points indicate the average over the 3 days per bird. Repeated measures GLM: chaff/seed ratio, F2,21=4.15, P=0.030; day, F2,21=2.74, P=0.087. Regression equation: y=3.65+0.09x.

View larger version (9K): [in a new window]   Fig. 7. Laying interval in relation to chaff/seed ratio in the six weeks preceding the day that nesting material was offered and all birds were given food without chaff. Laying interval was defined as the number of days between the day that nesting material was offered and the day the first egg was laid. Closed and open circles indicate pairs where feather were plucked or not plucked, respectively.