Nectar availability and flower choice by eastern spinebills foraging on mountain correa

Abstract

Nectarivorous birds are known to make choices at the landscape, plant species and individual plant levels when selecting foraging sites. However, little attention has been given to the fine-scale foraging choices that nectarivorous honeyeaters (Meliphagidae) make, such as those between individual flowers. We examined the variability in nectar availability between individual flowers of mountain correa, Correa lawrenciana, and used this information to predict the foraging behaviour of the eastern spinebill, Acanthorhynchus tenuirostris, a small (10–15 g) member of the Meliphagidae. Eastern spinebills preferentially foraged upon mountain correa flowers that were at the developmental stage offering the greatest volume of nectar. They did not discriminate between the flowers on the basis of corolla length (size), but this was not unexpected as nectar production was not correlated with flower size. Eastern spinebills were significantly less likely to forage at flowers with visual evidence of having been robbed of nectar by vertebrate and invertebrate competitors. They did not discriminate against flowers containing the flower mite, Hattena floricola, even though the flowers produced significantly less nectar when mites were present. This is the first study to show that a member of the Meliphagidae is capable of discriminating between individual flowers, favouring those most likely to contain most nectar.