The foods of insectivorous birds at Kowhai Bush, Kaikoura

Abstract

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ABSTRACT This study was designed to test a new method for researching the foods of passerine birds. The study site was located at Kowhai Bush, near Kaikoura, and consisted of successional Kanuka forest with little undergrowth. A grid system was used and most native birds were colour banded for the study. Chicks of five species of passerine and one species of cuckoo were removed from nests before fledging age, and placed in specially constructed artificial nest cages. Parents accepted cages readily and fed the chicks through the bars. Food items dropped in the nest and not retrieved by the adults were counted, weighed and identified. A video-camera was used to record the number and length of feeding visits parent birds made to nests. An estimate of the total daily food requirement was made.

Caging caused feeding rate and duration to increase, but chick weights were not significantly different to chicks in natural nests. Survival of chicks in cages was better than survival of naturally reared chicks for three species.

Applications of the caging technique include protecting chicks from predators, preventing chicks from leaving the nest before fledging, investigating food fed to chicks, developmental studies, and moving chicks to locations more convenient for research. The technique should be particularly useful in conservation biology.

Analysis of food items showed that some resource partitioning occurred between bird species. It was concluded that dropped items were representative of a nestlings diet. The use of caging as a non-destructive method of collecting feeding data was compared to the analysis of stomach contents and faeces. The results of the dietary aspect of this study have applications for wildlife management.