Towards a mechanistic understanding of elevational range occupation and territorial behaviour in tropical montane songbirds

Tropical mountains are some of the most biodiverse environments on earth. Typical of these gradients are the distinct elevational ranges of species along them, where related species occupy narrow elevational distributions that infrequently overlap. The mechanisms maintaining these patterns remain poorly understood, however, hampering our understanding of the processes that have created them, and our ability to accurately project changes along them in the face of warming climates. Similarly poorly known is how, or whether, life-history characteristics of tropical species mechanistically relate to their physiology/energetics. It has been hypothesised, however, that the lower metabolic rates of tropical species arise either from adaption to warmer, more stable tropical environments, or from the direct energetic costs associated with innate species characteristics (such as their behavioural traits).

This thesis addresses these two topics by studying tropical montane songbirds in Mesoamerica. Firstly, I assess the drivers of elevational range segregations along tropical mountains in line with three longstanding hypotheses; physiological specialisation to elevation-specific microclimates, habitat preferences and interspecific competition. Secondly I explore how the physiology of montane songbirds differs between seasons, and between species that occupy different elevational ranges. In addition, for one species I assess whether physiological shifts drive territorial behaviour, consistent with the suggestion that the pace of life of tropical birds is innately linked to their energetic expenditure.