Physiological mechanisms are studied in a wide variety of organisms, either because we are intrinsically interested in these organisms, or because they provide a good “model system” in which to study the mechanisms under investigation. Such a phylogenetically broad approach allows us to derive general principles of physiological functions and adaptations to similar ecological challenges across different clades. Birds can have advantages over mammals for studying some aspects of physiology. For example, the developing embryo is much more physiologically independent from its mother, allowing for easier access and manipulation. Some bird species are also better models of humans than rodents are, because of their diurnal lifestyle, social monogamy and relatively long life-span. Here, however, I will focus on using birds as a system in which we can investigate the physiological mechanisms underlying well-studied behavioural adaptations to ecological challenges. Food-hoarding behaviour in titmice has been studied for over 4 decades as a model system of behavioural adaptation to harsh winter conditions[1] and a model of the evolution of cognitive systems (spatial memory and the hippocampus)[2]. To date, however, very little is known about the physiological mechanisms that drive the motivation to hoard food in these birds. We have started this investigation from observations about the environmental conditions that drive food hoarding behaviour. We note that the same short day and low temperature conditions that drive the motivation to eat also drive the motivation to hoard. This makes us hypothesize that the mechanisms underlying the motivation to eat and the motivation to hoard are probably at least partially shared. In support of this, chronic moderate experimental elevation of corticosterone increased both food intake and hoarding motivation[3], while systemic injection of ghrelin or leptin suppressed food intake and food hoarding in these animals[4]. In birds, these peripheral hormones have different functions from the way they work in mammals. Understanding how birds and mammals have solved similar evolutionary problems, using similar ingredients, but in different physiological ways gives us deeper insight into how the evolution of physiological mechanisms works. We are currently investigating the gene expression of small peptides in the brain and peripheral tissues that we hypothesize to signal energetic state and gut fill in titmice. Once we have identified genes signalling nutritional state, we will investigate the effect of their encoded peptides on food consumption and hoarding behaviour.