Westerterp K. (1973) The energy budget of the nestling starling Sturnus vulgaris, a field study. ARDEA 61 (3-4): 137-158

In the 1968, 1969, and 1970 seasons a study on the energy balance of nestling Starlings was conducted, in a small colony founded for this purpose by placing nest-boxes on the border of pasture land in the national park 'De Hoge Veluwe' near Arnhem. Observations included food uptake, faecal production, growth, and energy devoted to maintenance and temperature regulation. Parental feeding frequency was measured by automatic recorders, and energy intake specified by combining this information with bomb calorimetry of sample meals collected throughout the nestling period by the collar method. Energy lost as 'rejecta' (faeces + urine) was determined by sampling faecal pellets regularly, and observing the rate of defecation during several 24 hours watches at the nest. Growth in weight was followed in seven nests, and sample young analysed at every day of age to enable computation of the energy incorporated in the body. The energy devoted to maintenance and temperature regulation was determined by measuring gaseous exchange in a respirometer at various temperature settings during the night when the nestlings were least active. All observations were conducted on intact broods of four, the most common brood-size in the study area. A preliminary energy budget between the age of 4 and 16 days of age showed the following. Energy lost as rejecta increases from 20% on day 4 to a plateau value of 40% from day 10 to 16, expressed as per cent of the total energy intake. Energy retained in the body as growth declines from 41% on day 4 to 11% on day 16, as per cent of the net uptake (the metabolizable energy or ME). Energy devoted to maintenance constitutes a constant 55% of the ME, whereas the supplementary heat production required for temperature regulation accounts for an additional 2-8% of the ME. When growth, maintenance and temperature regulation are subtracted from the ME, a fraction, rising from 3% on day 4 to 26% on day 16 is unaccounted for, and this is assumed to represent the expenditure for activity (gaping for food, scrambling about in the nest-box). Gross growth efficiency in the Starling was found to be 14% and net growth efficiency 22%, figures closely similar to those previously obtained for the Domestic Fowl, and rather lower than those reported for various fish-eating non-passerine birds.