Exploring the Brain and Behaviour of a Reverse Keystone Species, The Noisy Miner (Manorina Melanocephala)

Abstract

<p>The aim of this thesis was to study the cognitive complexity of the noisy miner <i>(Manorina melanocephala)</i> in an attempt to better understand its success in urban environments. Furthermore, the thesis aimed to use this species, not widely known for its cognitive prowess despite possessing complex behaviours and the proposed tool-kit for intelligence, to better understand potential indicators of cognition, namely, whether brain size is an accurate gauge of intelligence. </p><p>We first sought to conduct species-specific behavioural studies to test aspects of noisy miner behaviour that may assist their navigation of novel environments. Adapting the mirrormark test, we identified that noisy miners quickly habituate to reflective surfaces, following a behavioural sequence that initially begins with conspecific/social behaviours, and ends with the bird disengaging, and thus saving energetic costs, from the surface. We then investigated whether noisy miners were capable of “true” individual recognition, a complex behaviour that involves the ability of receivers to not only recognise a signaller, yet place a reliability status to this signaller regardless of context. Noisy miners not only reduced responses to unreliable signallers, they maintained this response across vocal contexts, indicating that they are capable of distinguishing individuals based on vocalisations alone, a characteristic likely maintained through their use of vocalisations to facilitate cooperative events such as group mobbing of predators.</p><p>Finally, we challenged the cognitive capacity of noisy miners through studying whether they could identify individuals of another species, humans, and allocate these novel people as “good” (providing food) or “bad” (captured individuals in nets) based on interactions. We identified that noisy miners rapidly learned to summon colony members upon seeing the “good” mask, yet would respond harshly with terrestrial alarm calls (more syllables at higher frequencies and rates) upon seeing the “bad” mask after the aversive events. </p><p>We next developed a high-throughput, non-biased quantification method to measure neuronal density and identify nuclear sizes using flow cytometry. The results obtained were comparable to those identified using stereological counting methods and consequently we employed this method to determine neuronal density of the noisy miner. Despite being an avian species, the procedure proved efficient across taxa and provided clear and repeatable evidence that noisy miners possess greater neuronal densities than Wistar rats (<i>Rattus norvegicus</i>), a species known for their success in cognitive challenges such as the radial eight-arm maze, where the species flexibly adapts to changes in food location. However, the noisy miner, a species to which this challenge is not standard, proved to make fewer errors during trials, thus demonstrating greater behavioural flexibility. We interpret the greater behavioural flexibility of the noisy miner compared to the Wistar rat as a result of the species possessing greater neuronal densities, with size of cells across the two species not being significantly different, therefore resulting in noisy miners having a shorter distance between cells for signal transmission.</p><p>The density of neurons, composed of cells packed closely together, likely facilitates the cognitive complexity and behavioural flexibility that this thesis confirmed through the behavioural studies on the noisy miner. Subsequently, this ability to rapidly adapt allows for the success of the noisy miner even in the most rapidly growing urban areas. We propose that in having a comparable measure of cognitive complexity (i.e. method to measure neuronal density across taxa), that this approach could be applied to other species so that we can gain an understanding of those species most likely to be affected by further urbanisation and anthropogenic changes.</p>