Science in the field: Superb Fairy Wrens
It was an overcast morning when we walked into Campbell Park, kangaroos stared disinterestedly at us while munching grass. The researcher we had just met had taken her boots off and was standing in calf deep cold water reaching into a blackberry bush. With feet sinking into the mud, arm buried among the thorns, Claire carefully reaching into a superb fairy-wren nest. She soon emerged victorious with three tiny wren eggs in her hand. Carefully stepping out of the cold mud Claire went off to measure the eggs. Oh the glamour of research!
Claire Taylor is in the 3rd year of her PhD studies at the Australian National University. She is looking at factors that influence maternal investment within superb fairy-wrens. So far this has involved a lot of field work, with 32 breeding pairs of wrens being monitored in this field season alone. The season runs from September to February, although this can be cut short if there is a week of hot weather early in the new year.
“We haven’t studied it” said Claire, “but it could be parents aren’t able to maintain their body condition or there’s a short supply of insects during hot conditions, its an interesting observation we’ve seen over the 20 years of field work.”
The heat, especially those 40-degree days, can slightly speed up the incubation process, though not by more than a day. All of this potentially has interesting implications as the climate continues to undergo change. A greater percentage of hot days like is predicted could impact breeding and incubations, though this isn’t part of Claire’s work currently.
Claire spends a decent chunk of every day walking around Campbell Park in all weather conditions, looking for new nests, checking eggs and feeding birds as part of a food supplementation experiment.
Fairy-wren nests suffer high levels of depredation from other birds and snakes snacking on eggs or chicks. While these nests are brilliantly camouflaged and hidden in blackberry bushes, using the same nest after a predation event isn’t an ideal fix. This means the wrens will choose a new spot to rebuild the nest and lay another clutch of eggs. Over the season they can have up to 8 breeding attempts each with up to four eggs. And with a 1.5 gram egg from a nine gram bird that’s a significant amount of effort going into producing offspring consistently in one season. I had no idea breeding for these tiny birds was so difficult!
“There was one bird”, Claire said, “who spent eight years brooding clutches, but through all those breeding seasons only raised one set of chicks to adulthood, that was in 2018”.
These little birds really are determined not to fail!
“Like a lot of animals that invest time into multiple breeding events in a season, they end up with very high predation rates, somewhere in the order of 66% of nests for wrens”, Claire told us as we followed her deeper into Campbell Park, “the danger zone is the first year, after that survivorship increases as the birds become part of the population”.
Superb fairy-wrens are also a victim of the Horsfield’s bronze-cuckoo, which features in Claire’s research. The adult cuckoo is twice as large as a fairy-wren and is a brood parasite. This means it will lay its egg in the wren’s nest. The cuckoo chick hatches and pushes the wren chicks or eggs out of the nest so it can receive all the food from the parent wrens.
“The interesting part is the cuckoo chick usually spends its first two days of life busily shoving an egg only just smaller than itself out of the nest before the wren hatches” said Claire.
When monitoring the nests, Claire checks regularly to see if any eggs have been laid. To do this she first checks the area for predators, like kookaburras, currawongs or magpies. If these are nearby, she waits for them to move away or if they’re taking their time, walks towards them so they fly off. Needless to say, some of these predators prefer to hop from fence post to fence post rather than move on straight away. Once the coast is clear, Claire can stick her hand among the blackberry thorns into the nest. There were 3 eggs in each of the nests we checked. They are white with reddish brown spots, typically forming a halo around the wider end of the egg. It’s hard to convey how delicate they are, weighing only 1.5 grams and measuring roughly 17 millimetres long, I’m definitely too clumsy to ever hold one! Claire carefully weighs each egg, measures them using callipers and takes a photograph of the clutch. While each egg takes its turn, an assistant with warm hands carefully holds the others, this is another job not suited to me with my reptile-like body temperature but was perfect for Mitch.
While walking to the next nest Claire told us how the wrens actually make their tiny nests;
“First, they collect spider web and shape it into a donut-like ring. Next, they collect sticks and twigs to form the nest structure around the ring, before making the nest cosy by lining the inside floor with crimson rosella belly feathers or kangaroo fur”.
The nests blend so well into the blackberry bushes that finding them is a skill in itself. Once, Claire is lucky enough to see a wren flying into a bush with a stick in its beak, this leads her straight to the nest under construction. It also looks quite comical to see a small bird carrying such a large twig.
The final nests just had to be checked to determine if any eggs had been laid yet. We went off track a little and through the bush on a hilly walk. The clouds were finally starting to disperse and the sun was struggling to shine through. At the last nest we came across a shingleback lizard sunning itself on the ground nearby, but no eggs.
Back at the carpark Claire showed us her nest book. It contained carefully recorded details for each nesting pair, including the band colours for each bird and updates on each date detailing things like nest building progress or the age of eggs.
“It started extremely detailed, noting location of the pairs and how to find the nest” Claire told us, “it’s become more of a shorthand now I know where I’m finally going”
We’re hoping to get out another day with Claire and, fingers crossed, see some wren chicks!
…A month later we got the chance to go out again. Claire emailed Friday night,
“I’ll be banding a clutch of chicks tomorrow and was wondering if you had a spare hour in the morning to come out?”
Of course, who would knock back an opportunity to see wren chicks!
So, Saturday morning we met at 7am and headed off to the nest. Passing a dried out dam, we reached the right blackberry bush and Claire stopped a short distance away to prepare. She pulled out a plastic container full of tiny, different coloured metal pieces, a scientific beading kit?
“All the wrens in the project have a numbered silver band and two coloured bands so I can identify the birds and easily tell who is from which clutch” Claire explained.
“I’m an R class bander which means I can band the superb fair-wrens without supervision, over the past few years I’ve banded almost 300 wrens”.
Sticking her arm among the thorns of a blackberry bush Claire, reached into a well concealed nest. She pulled out a small black pin feathered chick. Two other eggs were inside, but those probably wouldn’t hatch now. An adult male wren scurried around in the bush.
“He’s doing a rodent-run to draw us away from the nest” Claire said.
Back at the banding station Claire weighed the tiny bird, carefully settling it onto a cotton wool covered bowl to place it into the scale. She used callipers to get a tarsus measurement (the birds leg between the knee joint and ankle, where the foot begins). This will compare the size of the chicks in different experimental treatments as the weight may change depending on how recently the chick was fed. Next the little chick was blinged up, the silver numbered tag was put on its left leg, to differentiate it from the banded wrens at the Australian National Botanic Gardens which all had this tag on their right legs. The coloured tags given to this little one were green-mauve and red-blue, which gives the wren its name gmRB.
During the whole process the little chick looked very relaxed, I thought banding would be difficult but the little one was very cooperative and stayed still. There was a lot of chirping, its surprising how much noise can come from such a small animal.
“The chick in this nest is 7 days old, it’s got its pin feathers already and is just starting to get some fluff”.
Then Claire offered me the chance to hold the baby! I couldn’t get over how small it was, the little bird was so warm in my hand. It’s amazing to think if I come back in a few months this little wren might survive the odds and be flying around the park. Moments like these really put me into a researchers shoes and I can begin to understand the amazing things they get to do and see which so many people never will. Claire reclaimed the baby and popped it back in the nest, definitely the highlight of our day!
Over the next few months Claire will be back out every day, checking nests and continuing with the feed experiment. We’re lucky to have joined her for part of the amazing work she’s doing and see what other people get up to in their day job. Looking forward to hearing the findings of her research as it unfolds.
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