Information use during foraging by New Zealand bellbirds (Anthornis melanura) : A thesis submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy at Lincoln University 

Abstract

Nectivorous foragers rely on patchily distributed, static resources of highly variable quality. The ability to learn and remember information concerning the spatial distribution of available resources, and to associate this with variation in resource quality, is an adaptive trait for many nectivorous species. I examine informed foraging in regard to the New Zealand bellbird (Anthornis melanura). Bellbirds are facultative nectarivores; although they demonstrate an affinity for nectar, they readily switch to alternate food sources when it is unavailable. Informed foraging by nectarivores has largely been examined with respect to more highly specialised species (e.g. Trochilidae). Focus on a facultative nectarivore allows for examination of cognitive constraints in a less specialised system, where the availability of nectar poses fewer restrictions on forager behaviour. The first part of this thesis explored information use in natural environments by assessing engagement in resource tracking by bellbird populations at two spatial scales (Chapter 2-3). At a local scale, the nectivorous activity of resident bellbirds within 1 ha plots of native bush was correlated with spatial patterns of flowering for four key nectar species. The strength of the tracking response observed was linked to the pollination syndrome of the focal plants. Availability of ornithophilous plant species elicited stronger and more consistent tracking responses than the availability of entomophilous species. At a larger, landscape scale the movements of seasonally transient birds were quantified using a dialectal song type matching technique. Dispersal was found to be more distance limited than previously assumed. This suggests that large scale resource tracking may operate at an intermediary patch scale, rather than at a landscape scale. The second part of this thesis examined the cognitive mechanisms that may underlie informed foraging behaviours. I performed a series of experimental feeder trials on free-living male bellbirds (Chapter 4-6). Trials examined the ability of individuals to return to the location of a highly rewarding feeder within an array of less rewarding feeders. Treatments varied with respect to the reward concentration, the duration of the withholding period, the presence of visual cues, and the size of the experimental array. Bellbirds were found to have accurate spatial memory. Individuals were able to relocate rewards across a range of concentration treatments, retain spatial information for periods of up to 20 days, learn to associate visual cues with reward characteristics, and use spatial cues in a scale dependent manner. Overall, my research indicates that bellbirds were capable of engaging in memory informed foraging on nectar resources. Targeted exploitation of resources across multiple spatial scales likely translates to increased foraging efficiency. Low dietary dependence on nectar is associated with flexible usage of informed foraging, rather than a lack of cognitive ability in this species.