Clara Borrel (PhD student, School of Life and Environmental Sciences, Deakin University)

Endemic to the Southeast of Australia, the Spotted Pardalote (Pardalotus punctatus) is often heard but rarely seen. This diminutive bird, one of Australia’s smallest, inhabits a variety of environments including farmland, urban areas, coastal regions, and woodlands. However, its elusive nature, due to its preference for foraging in the canopy, nesting in burrows, or darting through the air like a bullet, makes it a challenging sight for observers.

Despite its cryptic behaviours, bird enthusiasts across Australia appreciate the beauty of the Spotted Pardalote. Yet, these birds remain understudied, with much of their core breeding biology remaining unknown.

My project aims to fill the knowledge gap on the breeding biology of these birds and study their breeding behaviours. I primarily study two behaviours that caught my attention when I was working on a pilot study on this species in 2019 under the supervision of Dr. Christa Beckmann and Dr. Kristin White. 1) parents seem to coordinate their breeding behaviours at the nest, both during incubation and chick rearing. During incubation, parents take turn and leave the nest very rarely unattended. During chick rearing, parents come to feed their chicks either in alternation (one after the other) or in synchronisation (together at the same time).  2) parents vocalise from and near the nest (on their favourite perch) when they are both visiting the nest at the same time.

I pondered the evolutionary significance of these behaviours. Coordination of parental behaviours has long been theorised as a means to resolve the sexual conflict supposedly inherent in biparental care systems. This conflict arises when each partner seeks to maximise its own fitness at the expense of the other, potentially destabilising biparental care. Coordination, however, serves to stabilise this system by resolving such conflict. Additionally, from a nest predation standpoint, it seems logical for parents to coordinate their behaviours to minimise the risk of attracting nest predators using visual cues.

Yet, the purpose of vocalisations at the nest, especially in a species as cryptic as the Spotted Pardalote, remained intriguing. Why would they risk attracting nest predators by signalling the nest’s location?

Following my pilot study on the Spotted Pardalote in 2019, I pursued my master’s thesis on the breeding behaviours of the Little Auk (Alle alle) under the supervision of Dr. Katarzyna Wojczulanis-Jakubas and Dr. Antoine Grissot. Here, I delved deeper into the coordination of breeding behaviours, a subject that introduced me to the emerging trend of cooperation between partners in socially monogamous birds. Through the works of researchers like Dr. Katarzyna Wojczulanis-Jakubas and Prof. Simon Griffith, I gained insight into the age-old debate between competition and cooperation in evolutionary biology, and the underlying human socio-ideological conflict: is (human) nature good or bad? Is (human) nature altruistic or selfish? I eventually came across the research of Prof. Joan Roughgarden and her views on social selection which states that there will be instances of sexual conflict between partners but places a stronger emphasis on social negotiation between partners to ensure the successful production of offspring, thus highlighting the importance of communication between individuals. It then made sense; coordination does not have to be seen as a way to solve the sexual conflict but can also be viewed as a purely cooperative behaviour. Moreover, the cooperative framework was giving me more keys to understand these conspicuous vocalisations tied to the incubation exchange/chick feeding behaviour. Partners could be communicating to coordinate and share the parental duties, and this could be a form a cooperation. This point of view, is particularly relevant in the case of socially monogamous birds, such as the spotted pardalote. In such a system, breeding partners stay together for more than one breeding attempt, so neither partner has an interest to overexploit the other as this overexploitation may affect the fitness of the pair as a whole.

From there, I came up with two main hypotheses to be tested 1) coordination improves the breeding success of the pair as a whole. 2) vocalisations at the nest are a mean for partners to negotiate over care. To study the coordination at the nest in the spotted pardalote, I first monitored the birds on camera. To study the vocalisations at the nest, the birds were recorded in-person using a shotgun microphone.

I now finished my first field season (August 2023-March 2024). With the help of my incredible field team – Ryan Boutland, Zoé Miquel, Sacha Carré, Nicole Tielemans, Juliet Bao Ngoc Doling, Raine Lago-Meckes, Callum Clark, Amy Edwards, Caitlyn Edwards, Sarah Cherri, Carol-Ann Chabot, Théodore Vanrenterghem, Beth English, Gargi Bakshi and Cim-Héloïse Sävel -, the infinite support of my supervisors – Dr. Christa Beckmann and Prof. Peter Biro -, the funds from the Holsworth Wildlife Research Endowment, the Stuart Leslie Bird Research Grant and the Geelong Field Naturalist Environment fund; I monitored 108 nesting attempts, recorded 25 pairs on video during incubation and 18 during chick rearing to study coordination, and recorded 17 pairs in-person during incubation and 18 during chick rearing to study the vocalisations at the nest. These birds have only been more surprising and beautiful every day, they exhibited a greater diversity of calls and behaviours than what I had witnessed during the pilot study in 2019. The data is now left to be processed, before we get ready for a second round from August 2024 to March 2025 where I will introduce a PIT-tag based method to study continuously the fine-scale breeding behaviours at the nest of the most charming Australian bird. I hope my PhD will provide a contribution to the evolutionary framework of cooperation so that interactions between individuals can also be viewed as driven by mutual success, and not only by competition.

Clara Borrel was recently awarded a Holsworth Wildlife Research Endowment grant to help support this research.

Image credits: Callum Clark and Carol-Ann Chabot