Nicholas Yu, Macquarie University

An article I wrote for BirdLife Australia last year describes the predation of nestling Eastern Yellow Robins by an Eastern Ringtail Possum, a Pied Currawong and likely attempted predation by a Red Wattlebird. Although Eastern Ringtail Possums have been inferred to be predators of birds’ nests, the observations presented in my article appear to be the first unequivocal evidence of carnivory in that species and offer new insights to this possum species’ ecology.

Predation is one of the most significant selective pressures in the natural environment that shapes the evolutionary relationships within many systems. The nest is part of a critical phase in a bird’s lifecycle, when the bird is confined to a specific location. To a large extent, these selective pressures regulate bird biology. Therefore, nest predation has attracted much attention from ornithologists as it is a key source of evolutionary selection in birds. In the present study, videos were used to identify predators and potential predators at the nest of a pair of Eastern Yellow Robins in an urban area in eastern New South Wales.

In November 2022, I noticed an Eastern Yellow Robin nest in the fork of a Small-leaved Privet growing in a disturbed bushland park at Macquarie Park in eastern New South Wales. On 6 November, I inspected the nest revealing three eggs. I installed a trail camera on a nearby Broad-leaf Privet, opposite the nest, to monitor any activity. The nest was monitored 9 to 29 November.

Video footage taken by the camera revealed two adult Eastern Yellow Robins taking turns monitoring and incubating the eggs as well feeding the chicks when they had hatched. On 19 November, one of the Robins was sitting on the nest and showed behaviour that resembled distress, possibly even defending the nest from a Red Wattlebird that was perched on a vertical trunk of a Small-leaved Privet, below the nest. On two occasions, the Wattlebird attacked the adult Robin on the nest, while a second Robin was attempting to distract the Wattlebird. The Wattlebird eventually flew off. I inspected of the nest at same day and noticed two of the three eggs had successfully hatched.

Footage from 22 November at night, showed an Eastern Ringtail Possum removing and consuming one of the chicks from the nest. The chicks could be heard making agitated calls as the Possum climbed up the privet towards the nest, reached inside the nest, grabbed one of the chicks with its teeth, and transferred this to its left front paw. In the 23 seconds of footage recorded while the Possum consumed the nestling, the nestling was clearly still alive – i.e. there was no fatal bite to kill the nestling before consumption. The video did not record the full duration of the consumption event, although it is presumed that the chick was fully consumed as no remains of the chick could be found near the nest. The adult Robins returned to the nest the following morning and continued to care for the remaining chick and egg.

Further footage from 23 November showed the nest was visited by a Pied Currawong. I could see the Currawong was perched on the privet below the nest for 7 seconds before grabbing one of the other chicks with its beak and flying out of view of the trail camera. The Robin chick could be heard making distress calls when it was seized by the Currawong. Sadly, this was also the last time the adults were seen at the nest, it is presumed that they abandoned it.

There was no evidence of the only egg being consumed during the Possum’s and Currawong’s visits, although a visual inspection of the nest on 26 November revealed that the remaining egg had a minor crack on it and did not survive. The Eastern Yellow Robin nest was also visited by an adult Eastern Ringtail Possum on 25 and 29 November though no predation occurred. Whether it was same possum is unknown. 

My study at Macquarie Park highlights a diversity of potential and actual predators at a single Eastern Yellow Robin nest. Nest predation of small bird species by Pied Currawongs has been well documented by a number of studies. Red Wattlebirds are also known predators of birds’ eggs. The most significant of my observations was the consumption of a nestling Eastern Yellow Robin by Eastern Ringtail Possum. Like other ringtail possums, Eastern Ringtail Possums are primarily folivorous, but and also eat flowers and fruit. Major reviews of ring-tailed possum diet do not document consumption of vertebrates, but a few studies infer Eastern Ringtail Possums as predators of birds’ eggs or nestlings although observational evidence of this does not appear to have been published.

My observations and videos offer new insights into Eastern Ringtail Possum ecology, including the method of predation, consumption rate and multiple return inspections of the nest by the species. This is the first properly documented observation of carnivory in the family Pseudocheiridae, joining members of the families Phalangeridae (brushtail possums, cuscuses) and Petauridae (wrist-winged gliders and relatives) as known diprotodont marsupial predators of birds’ eggs and nestlings.

In urban bushland environments where optimal habitat for nest building is limited, predation of nestlings by other passerines and arboreal mammals may reduce Eastern Yellow Robin breeding success. From a broader context, my observations further contribute to our understanding of predation pressure on urban birds.

Further information and YouTube videos on my article can be accessed online in Australian Field Ornithology at: https://afo.birdlife.org.au/afo/index.php/afo/article/download/2298/2324

Image credits: Nicholas Yu