Brood Division and the Ontogeny of Caching Behaviour in the North Island robin (Petroica longipes)

Abstract

<p>The post-fledging period is an important, but understudied, stage of avian development. This is despite the fact that the parental care and behavioural development of young observed during this period contribute significantly toward offspring survival. A key factor that has contributed to the lack of research in this area has been the difficulty with which parents and offspring can be observed during this period. The North Island robin (Petroica longipes) is a small insectivorous passerine native to New Zealand forests. As a result of the historic absence of mammalian predators, North Island robins lack pronounced anti-predator behaviours and are fearless towards humans. This makes them ideal subjects for behavioural studies in the wild because human presence does not alter their daily activities. Using field observations, the present study examined parental care and the development of caching during the post-fledging period in wild North Island robins. Brood division is a form of preferential post-fledging care that is well documented among avian species in the northern hemisphere. In contrast, little is known about the incidence and function of brood division in avian species outside this region. Across two breeding seasons (2014-2015 and 2015-2016), feeding interactions between parents and offspring were observed during nestling and fledgling development to determine the timing of and factors influencing brood division in robins. Brood division occurred around the time young left the nest and was common amongst broods which fledged two or more young. The male parent typically cared for male and larger fledglings and the female parent for female and smaller fledglings. The results of this study match patterns observed in northern hemisphere species suggesting that brood division provides the same adaptive advantages to species regardless of geographical context. Caching, the handling of food to preserve it for future consumption, is an important strategy which allows numerous avian species to deal with natural fluctuations in food supply. In recent decades, caching has become a widely-used paradigm for examining a range of cognitive processes in birds, such as social cognition and spatial memory. However, much is still unknown about how caching develops in young birds, especially in the wild. Over a 12-week period following fledging, the ontogeny of caching and cache retrieval was observed for 34 juvenile robins. Juveniles began caching shortly after achieving foraging independency (approximately 5 weeks after fledging) and their caching rates increased gradually with age. Retrieval of caches began spontaneously as soon as they had begun to cache and retrieval rates remained constant throughout development. Results suggest that caching behaviour in North Island robins is likely to be innate, but that age and experience have an important role in the development of adult caching behaviours. The two studies described in this dissertation examine behaviours that have either been previously difficult to document in the wild or have not been documented in this species. Overall, the results highlight the behavioural similarities between the North Island robin and other avian species exhibiting brood division and caching. Additionally, they also demonstrate the suitability of the North Island robin for future behavioural research given the ease with which these birds can be observed in the wild.</p>