FLESHY FRUITS OF INDIGENOUS AND ADVENTIVE PLANTS IN THE DIET OF BIRDSIN FOREST REMNANTS, NELSON, NEW-ZEALAND

The relationship between fleshy-fruited indigenous species and adventi ve weeds in the diet of 500 mist-netted birds was studied in forest re mnants of differing size and degree of modification. Fruit abundance p eaked in March and April, and most fruit was either red/orange or purp le/black. The physical parameters of adventive and indigenous fruits w ere not significantly different. Six of the 15 passerine species nette d are frugivores, and of those netted 77% had eaten fruit. They were d ivisible into three groups: endemic (bellbirds, Anthornis melanura; tu is, Prosthemadera novaeseelandiae), non-endemic but indigenous (silver eyes, Zosterops lateralis), and adventive (blackbirds, Turdus merula; song thrushes, T. philomelos; starlings, Sturnus vulgaris). Bird diets varied between the groups and according to fruit availability as dete rmined by sires and seasons. Endemic birds ate the least adventive fru it; bellbirds ate mainly Podocarpus hallii and Coprosma robusta fruits at all sites. Tuis had a varied diet, including some adventive fruits . Silvereyes ate the widest range of indigenous and adventive fruits. Blackbirds and, to a smaller extent, song thrushes ate many of the sam e indigenous fruits as the other bird groups, but their diet included more adventive fruits, e.g., Berberis glaucocarpa. Starlings were caug ht only when they fed on Sambucus nigra, but they also ate a few indig enous fruits. There was little seasonal variation in bird numbers caug ht. Adventive species extended the seasonal availability of fruits int o winter, particularly in the forest remnant closest to a town, which had the highest proportion of adventive fruits. Several weed species d istributed mainly by non-endemic and adventive birds are forming new s econdary vegetation. Some have large fruit crops which generally offer little food for endemic birds. Where fruiting weeds pre-empt sites th at may have been occupied by native species, they create an inferior h abitat for endemic birds. However, the non-endemic and adventive birds also disperse indigenous fruits into early successional vegetation, a nd the importance of their seed rain for conservation of biodiversity will therefore depend on the site.