Profile of an avian nectarivore community and its nectar resources in tropical woodland

Abstract

The abundance, species diversity, foraging behaviour and habitat choice of nectarivorous birds, and the availability of nectar, were studied in tropical woodland near Darwin over a six month period. The nectar supply was continuous but the dawn standing crop varied an estimated sixty-fold. Two species of lorikeet and nine species of honeyeater were present, and all made extensive use of nectar. Variable levels of dependence on nectar were exhibited by a further seventeen opportunistic species. The resultant community may be the richest avian nectarivore community documented in Australia.

Variations over time in both nectarivore species richness and abundance were strongly and positively correlated with the dawn standing crop of nectar. Most lorikeet and honeyeater species were present in the study area throughout the study period, and species richness varied mainly as a result of movements into the study area by opportunistic nectarivores. Changes in abundance, however, resulted primarily from fluctuations in the population of the most abundant honeyeater and nectarivore, the Little Friarbird Philemon citreogularis, complemented by smaller numbers of opportunistic nectarivores. The spatial distribution of nectarivores within the study site was positively correlated with the dawn standing crop of nectar for much of the study period, but the relationship broke down when nectar was most abundant.

Species richness was not mediated by flower structure. The diversity of nectar sources and/or the associated structural diversity of microhabitats may have contributed. Large honeyeaters and lorikeets preferentially foraged on eucalypts, whilst small honeyeaters preferred species such as Grevillea and Melaleuca, and there was a parallel dichotomy amongst opportunistic nectarivores. Levels of interspecific aggression were low for most of the study, even when there was relatively little nectar available. The diversity of opportunistic nectarivores was undoubtedly made possible by the abundance of readily accessible nectar in the latter part of the study period, facilitated by the local juxtaposition of habitats and the probable abundance of nectar over much of monsoonal Australia at the time.

Date of Award	Oct 1994
Original language	English
Awarding Institution	Charles Darwin University (CDU)
Supervisor	Richard Noske (Supervisor)