Fruit selection by birds in relation to fruit abundance and appearance in the naturalised shrub Berberis darwinii

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Abstract
The effects of three forms of fruit damage were tested on avian selection of the fleshy fruits of Darwin’s barberry (Berberis darwinii) from plastic trays, and compared with the abundance of fruits and their removal rates from nearby bushes, in December-January near Dunedin, New Zealand. Ripe fruits were removed from bushes by four bird species: blackbird (Turdus merula), song thrush (T. philomelos), silvereye (Zosterops lateralis), and kereru (Hemiphaga novaeseelandiae). The abundance of ripe fruits reached a peak 15 days after commencement of the study. Removal of the artificially presented fruits was negligible during this period. During the subsequent 15 days, as natural ripe fruit abundance declined, up to 80% of fruits were removed from trays within five days of presentation of fresh material. There was no significant change in fruit removal rate from bushes over the study period. Tray-presented intact fruits, with or without glaucous bloom, were clearly preferred to those with beak marks or simulated insect damage, irrespective of the abundance of the natural fruit crop. Shrivelled fruits in the trays were not eaten by birds. It is concluded that UV reflectance associated with the presence of a waxy bloom does not increase fruit attractiveness to birds, but that physical alteration of fruit surface or shape by marking, puncture, or shrivelling reduces fruit selection. Barberry fruit abundance does not affect the selection of damaged fruits.