Bud-feeding by bullfinches: methods for spreading damage evenly within orchards.
Abstract
To explore possible ways of reducing the effets of bud-eating in orchards, captive bullfinches [Pyrrhula pyrrhula] were studied in an aviary simulation of the orchard-edge situation. Sunflower seeds (representing fruit buds) were offered in a line of dishes leading from a simulated refuge thicket, and conditions were varied to test predictions from a mathematical model of how birds' feeding effort might be spread more evenly from the edge. Provision of alternative, less-preferred food in the thicket reduced feeding from the dishes and caused a stronger concentration of birds next to the thicket. Removal of the two dishes nearest the thicket consistently led to the desired spreading out of feeding, but filling the gap with less-preferred food did not achieve the same result. Mixing seeds with empty husks to make detection of seeds more difficult produced contradictory results. The study suggests that damage might be reduced by widening the orchard-edge gap, thus causing bullfinches to forage farther and so deplete fewer trees below a critical threshold of bud loss.<new para>ADDITIONAL ABSTRACT:<new para>To explore possible ways of reducing the effects of bud-eating in orchards, captive bullfinches were studied in an aviary simulation of the orchard-edge situation. Sunflower seeds were offered in a line of dishes leading from a refuge thicket, and conditions were varied to test predictions from a mathematical model of how birds' feeding effort might be spread more evenly from the edge. Provision of alternative, less-preferred food in the thicket reduced feeding from the dishes and caused a stronger concentration of birds next to the thicket. Removal of the 2 dishes nearest the thicket consistently led to the desired spreading out of feeding, but filling the gap with less-preferred food did not achieve the same result. Mixing seeds with empty husks to make detection of seeds more difficult produced contradictory results twice. The study suggests that damage might be reduced by widening the orchard-edge gap, causing bullfinches to forage farther, depleting fewer trees below a critical threshold of bud loss.