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

Abstract

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.

Diet of nestling LinnetsCarduelis cannabinaon lowland farmland before and after agricultural intensification

“…Woodpigeons are a major pest of developing Rape crops, grazing on the crop's foliage, leading to differential plant development (Inglis et al 1989). Thus even when the majority of the seeds are fully ripened and less suitable as a nestling food (Glück 1985), Woodpigeon-damaged areas are likely to still contain unripe seeds.…”

Weed seed resources for birds in fields with contrasting conventional and genetically modified herbicide-tolerant crops

“…(b) Weed seed composition Since seeds from different weed species vary greatly in size and composition (Earle & Jones 1962;Glü ck 1985;Diaz 1990), the abundance of weed seeds alone may be a poor measure of the true resource available to foraging birds. Because of this, we obtained weights and compositions of seeds of 305 weed species important in bird diets and present in the FSE samples.…”

“…In addition, the total energy contained within weed seeds important in each bird species' diet, in each half field, was calculated as the sum of the products of the number of seeds of each weed species and their energy content. Seed energy content was calculated as the sum of the energy contents of the seed lipid, carbohydrate and protein components, themselves calculated as the weight of each component (from seed weight and its percentage composition by weight) multiplied by componentspecific conversion factors of 38.94 kJ g K1 for lipid and 17.17 kJ g K1 for carbohydrate and protein (Glü ck 1985). We consider total energy content to be a measure of weed seed energy available to birds.…”

Post-dispersed pine seed removal and its effect on seedling establishment in a Mexican Temperate Forest

“…Granivores are able to select their food during their foraging activities (Gluck 1985;Hay and Fuller 1981) and this affects vegetation structure (Dupré and Ehrlén 2002;Orrock et al 2006;Veech 2001).…”