Deep within the heart of the Kimberley, tucked safely away among the palms of the pandanus that line the banks of Annie Creek and the Adcock River, hides an unusual group of fairy-wrens decorated in purple crowns.
“Everytime we do a new study we are surprised by how different they are from the other fairy-wrens,” says Dr Niki Teunissen, who alongside Professor Anne Peters at Monash University, has been researching the secret lives of these elusive birds as part of a 16-year research collaboration with the Australian Wildlife Conservancy.
The research project, which closely monitors a 15 kilometre stretch of land within the AWC’s Mornington Wildlife Sanctuary – home to one of only two known populations of the wren – has generated over 30 scientific papers giving us insight into the birds’ social lives, breeding behaviour and their famous purple crowns.
We now know, for example, that purple-crowned fairy-wrens, unlike other species of fairy-wren, don’t cheat on their partners.
We know that their purple crowns aren’t used to attract a mate.
We know that males and females perform duets.
And we know that their population has declined by over 50 per cent.
Niki herself recently published yet another paper revealing the motivations behind the wren’s so-called altruism. Unlike other birds, purple-crowned fairy-wrens put their own lives on the line by defending their social group.
“Our findings show that subordinate helper fairy-wrens expecting to inherit the top spot in the group invest in saving the threatened young so that they have a larger group later on when they are a breeder themselves,” Niki says.
“In other words, they are actually saving their own future helpers.”
For Anne, who grew the project from what was initially just a five-year research fellowship, Niki’s recent study exemplifies why she’s dedicated so much of her life to these birds.
“I love how complicated they are,” Anne says. “The more we find out about them, you realise as humans we underestimate the complexity of animal behaviours, and the complexity of the drivers behind those behaviours.”
Rather than altruism, purple-crowned fairy-wrens put themselves on the line in the hope of maintaining a large breeding pool. (Video credit: Niki Teunissen/AWC)
Getting up close and personal
The purple-crowned fairy-wrens of the Mornington Wildlife Sanctuary offer a unique opportunity for biologists such as Anne and Niki to observe a rare bird in close quarters.
“If you go and visit them and stay quiet, they’re quite tame,” Anne says. “That’s why we can do detailed observations on them.”
Anne recalls on one occasion – when sitting on the opposite river bank to a large, busy group of birds, eagerly trying to record each bird’s coloured band (how they monitor the birds) – one individual passed through the pandanus to perch on her head.
“Those are the sort of experiences that make the itchiness, sweating and frustration worthwhile,” she says
These coloured bands mean individual birds can be instantly recognised. “From when and where they are born to who their family is, when they breed, how many offspring they have and when they die, we always know exactly who we’re looking at,” Niki says.
Through these close observations, it became clear early on that purple-crowned fairy-wrens are monogamous. “They don’t cheat on their partners like other fairy-wren species and that was unexpected,” Anne says. “When I predicted it, my PhD supervisor, who’s studied fairy-wrens longer than me, laughed. But I ended up being right.”
To put this in perspective, 90 per cent of superb fairy-wren nests have at least some young in them that are from a different dad. “That was kind of the rule for fairy-wrens,” says Niki. “But purple-crowned fairy-wrens are an exception to the rule. They’re really faithful.”
Even when the female is preparing to lay eggs, the male stays within a few metres of her at all times.
Restricted to these riparian corridors of the Kimberley, it’s likely purple-crowned fairy-wrens are limited by their location and the number of available mates, making it both difficult and stupid to cheat on a partner.
That they don’t need to compete as hard as their counterparts for a mate has resulted in significant evolutionary diversions from other wrens.
Take for example, testicle size. The male superb fairy-wren faces tough competition to fertilise an egg because his partner will almost certainly have mated with another male; so he has to produce huge amounts of sperm, which results in his testes swelling to five per cent of his body weight. Purple-crowned fairy-wrens, on the other hand, have comparably smaller testes.
Then there’s that beautiful purple crown.
Superb fairy-wrens that transform into their striking blue breeding colours earlier in the year are preferred by females when looking to cheat on their partners. Purple-crowned fairy-wrens, however, don’t cheat. It begs the question: what’s with the crown?
Marie Fan, one of the project’s five PhD students, presented 3D-models of the purple-crowned fairy-wrens, each sporting either purple or dull colours, to the males of the group. Those painted in purple elicited the most aggressive responses.
Turns out, their purple crowns aren’t for the ladies, rather they’re used to compete and dominate other males.
If the purple-crowned fairy-wren doesn’t already sound like the ideal mate, here’s another feather in its cap: more than any other fairy-wren, it’s known to perform duets with its partner.
In 2009, a paper published by ornithologist Dr Michelle Hall and Anne, which used a playback experiment, found that mating pairs combined 50 per cent of their songs. According to the paper, this is important for cooperative territorial defence.
Basically, it’s a pretty efficient home alert system.
Land of drought and flooding rains
By now, the research team has witnessed their fair share of wet seasons, which Anne describes as a double-edged sword for the birds’ breeding success.
“It gets them to breed, but if there’s too much rain their nests get flooded,” she says. On more than one occasion the scientists have watched as nests are flushed down river. But no rain at all could be even worse.
Since 2018, the team have been studying the telomeres of the wrens. Telomeres are structures found at the end of a chromosome. All species, including humans, have them. They shorten and deteriorate with age, which is why humans have a lot of interest in studying them.
By studying the telomeres of a purple-crowned fairy-wren you can find out how long it will live and how many young it’ll produce. What the scientists are most interested in, however, is what shortens the telomeres.
A paper they are currently working on suggests that hot weather paired with a lack of rainfall has resulted in the wrens being born with shorter telomeres.
“This means the young live shorter lives and will have fewer babies in their lifetime, and that’s not what we want,” Anne says.
“It’s getting hotter and there are various problems with that. It would be better for the wrens if we could stop climate change from accelerating. I’d be more sanguine about their future.”
It’s not all bad news for the purple-crowned fairy-wren, however.
Since AWC acquired the land for conservation purposes back in 2004, its EcoFire Program has helped maintain the wren’s habitat.
“Before the EcoFire Program, the fires happened late in the dry season when it’s really hot and the fire was incredibly intense,” Niki says. “It wipes out anything in its path.
“Now, AWC does prescribed burns early in the dry season, around April and June, when it’s cooler and wetter, so if a fire comes through it burns in a mosaic pattern and a lot less is burnt.”
AWC also keeps cattle from trampling the wrens’ beloved pandanus.
“They’re not in the best situation,” says Niki. “Habitat degradation is still a problem across the Top End and we’re seeing how drought and high temperatures have huge impacts on these birds [and] that will [only] get more extreme. It won’t be good for them.”
Despite all of this, and because of the habitat management by AWC, Niki says she remains “hopeful for the population at Mornington”.