Seed preference and energy intake of Goldfinches Carduelis carduelis in the breeding season

The food of a population of Europeans Goldfinches breeding in Orchards was studied. More than 5% of the total foodstuff consumed was met by the seeds of seven food plants. Water, lipid, carbohydrate and protein content was determined from 20 different plants which Goldfinches used during the breeding season in order to calculate energy content. The energy of fresh seeds varied from 1.88 kJ/g in Tussilago farfara to 12.14 kJ/g in Dactylis glomerata. The dependence of the rate of energy intake (profitability) on the pecking rate and the size (weight) of the seeds was calculated. The profitability of various seeds is in agreement with the relative number of birds using them. Calculation of the feeding time that a Goldfinch needs during daylight hours, if it feeds only on a particular plant, indicates that there are several foods that cannot fill the energy demands of the bird during the breeding season. These are eaten only if others with a high energy content are not available. Thus food selection in Goldfinches depends, apart from availability, on seed profitability. The oxygen consumption of a male Goldfinch was significantly higher when the animal was feeding on seed heads of Tussilago farfara and Taraxacum officinale than when it fed on loose dry seeds, and so, different feeding techniques have to be taken into account in calculating net energy gain.