Form and function of on-nest vocalisation and renesting behaviour in the Grey Fantail (Rhipidura albiscapa)

Abstract

Nest predation is the most common factor impacting nest success in songbirds; therefore, we would expect behaviours present in populations to have evolved to counter this risk. However, there are behaviours present in songbirds that are risky and their benefits are unclear. One such behaviour is the presence of on-nest vocalisations; though important for intraspecific communication they increase the risk of nest predation. Therefore, we would expect birds to minimise on-nest vocalisation to decrease a predator's likelihood of finding nest locations. Yet, some songbird species continue to vocalise on the nest at high rates. Assessing behavioural trade-offs is an integral part of understanding the evolution of extant behaviours. The Grey Fantail (Rhipidura albiscapa) is an Australian flycatcher that has high nest predation rates. The adults vocalise on the nest and abandon a high proportion of nests during breeding season, making it an ideal model species to examine the costly behaviours of vocalising on the nest and nest abandonment. In this thesis, I study how on-nest vocalisations and nest site selection strategies, including nest abandonment, might be adaptive strategies to reduce nest predation risk. Using descriptive data, I define the occurrence of on-nest vocalisations and song types produced across nest stages and nesting attempts. The number of on-nest vocalisations decreased across nest stages but did not change with successive nesting attempts. Similarly, the proportion of song types used, and song type diversity did not vary across nesting attempts. My data shows vocal production appears to be strategic, potentially varying due to limited time during the breeding season and the energy costs associated with each nest stage. To examine nest site selection strategies, I used descriptive data to study nest placement of focal pairs in relation to neighbouring nests. I found focal birds placed nests closer to neighbours that were nest building and furthest from neighbours that were egg-laying. Matching neighbour activity during building could allow pairs to benefit from dilution and confusion effects, thereby reducing predation risk. Also, avoiding fertile egg-laying neighbours may save energy by reducing aggressive encounters. My thesis proposes that Grey Fantails strategically vocalise on the nest and make nesting decisions to save time and energy. This research contributes to an increased understanding of seemingly costly behaviours in relation to nest predation risk and provides further insight into the evolutionary strategies of nest abandonment and on-nest vocalisations.

Date of Award	2021
Original language	English