Nature
PUBLISHED
A pair of Leadbeater’s possums carries the fate of their species with them as they explore a protected area that’s been prepared for years just for them. The odds are stacked against the species surviving extinction, at least in the wild, but this pair is doing all one could hope for in caring for newborn twins, having survived personality differences and genetic separation to reproduce.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Leadbeater’s possum (Gymnobelideus leadbeateri) was once considered extinct, with no living examples seen between 1909 and 1961. Its range was always small, and the forests it calls home have been devastated by logging and megafires. Fortunately, the lack of sightings turned out to partially reflect its small size (33 centimeters, or 13 inches, including the ridiculously oversized tail) and nocturnal habits.
Nevertheless, the possum remains critically endangered, with any hope of survival dependent on a breeding program run by Zoos Victoria. Whether because they are the state of Victoria’s faunal emblem, or utterly adorable, the program has far more resources than many species receive, and benefits from the world’s largest longitudinal animal study. Unfortunately, the team are up against the fact the possum’s tiny and isolated populations lack diversity.
Consequently, the discovery of another colony of Leadbeater’s possum in 1986 in the Yarra ranges was particularly good news. These possums live at lower altitude than the other survivors. While not dissimilar enough to be considered a separate species, the lowland Leadbeater’s carry some genetic and behavioral differences from their (slightly) more common highland cousins.
“The highland possums can be quite feisty,” Nicole Boys of Healesville Sanctuary told IFLScience. “I’ve found the lowlanders are a bit more chill.” As a matriarchal species, this raised questions as to whether lowlander male Mercury could bond with highlander Narvi, but Boys’s team considered blending their genes the species’ best hope.
The pair were brought together in captivity, before being released last June into the Coranderrk Nature Conservation Area, a lowland habitat next to Healesville Sanctuary that’s been cleared of predators and made possum-ready. The breeders were recently pleased to notice a bump in Narvi’s pouch, signaling the presence of young, and even more delighted to witness the care the pair is taking of their bundles of joy.
“Mercury has been doing a lot of looking after the joeys,” Boys told IFLScience. “He’s keeping them warm while Narvi was out foraging for food. Being a lactating Mum is hard work.” This is particularly important because Leadbeater’s possums are cooperative breeders that live in small family groups. A monogamous pair does the family’s breeding, but others, usually their older children, help care for the young until they are perceived as threats and get kicked out to make their own way. With no one else to share the load, it’s just as well Mercury has stepped up.
Like giant pandas and kākāpō, Leadbeater’s possums sometimes seem like they’re determined not to be saved. Larger Australian possum species have adapted to city life with gusto, but the lowlanders live in swampy tangles of trees that have been compared to some out of a Tolkien novel. Both populations can only survive in medium-aged forests. After fires or logging, forest regrowth lacks the nesting sites Leadbeater’s need to breed. That’s a problem common to many animals, but Leadbeater’s possums are unusual in relying on foods that are rare in old forest. When their habitat either ages out of the critical window, or suffers a new disturbance, they need to find new territory fast.
Zoos Victoria planted almost 140,000 trees, starting a decade ago in preparation for a planned Leadbeater’s release. They’ve accelerated the conservation area’s readiness by providing boxes that can be used as nesting sites, and are also leaving food out to supplement what Mercury and Narvi can forage from the wild. Hopefully this luxury possum BnB will soon have more than just four residents.
Although mixing the highland and lowland genes is considered essential to avoid inbreeding, the lowland population is probably better adapted to the Healesville area, particularly as temperatures rise. Boys told IFLScience it’s likely the team will try to breed Mercury and Narvi’s offspring with other lowlanders, rather than maintain an even genetic mix.
Another obstacle to Leadbeater’s possums’ survival is that the matriarchal nature of the family dynamics means females tend to get kicked out of a colony earlier than the males, often when they’re less likely to survive. That creates heavily skewed sex ratios in the wild, but offers an opportunity for the Zoos Victoria team to support young females through the dangerous initial period on their own.
