Recent developments in photographic equipment and software has contributed to a proliferation of stunning wildlife images. Natural History curator Colin Miskelly describes how high-quality digital images have revealed previously overlooked or unrecognised ecological interactions between two ancient species that have been in Aotearoa for tens of millions of years.
Our smallest bird
Tiny and always on the go, the tītitipounamu | rifleman is a challenge for any photographer. They are a bird of the dark forest interior, typically foraging on the surface of tree trunks and large branches. When they do make their way towards the tree tops, they become hyperactive dots silhouetted against the bright sky.
Best-known for being our smallest bird, tītitipounamu are a very special member of our fauna. Along with their cousin the rock wren | pīwauwau, they are the only surviving members of the New Zealand wren family.
Although similar in appearance and behaviour to the true wrens of the Americas and Eurasia, New Zealand wrens are the most ancient lineage of songbirds in the world. They likely diverged from other songbirds more than 82 million years ago – around the time that Zealandia split from Gondwana.
A bucketlist bird
As one of Aotearoa’s ‘deep endemics’ tītitipounamu are one of the species that international birders hope to see when they visit. Australian photographer Glenn Pure first encountered them in beech forest at the northern end of the Routeburn Track, near Queenstown, earlier this year.
He was delighted to see small flocks of tītitipounamu searching for food among the leaf litter. He took hundreds of images of the obliging little birds, and did not realise until later how unusual his observations were. While tītitipounamu occasionally descend to ground-level, it’s very unusual to have flocks focussed on forest-floor foraging.
The right gear for the job
Glenn was curious to identify what the birds were feeding on, and hoped that his images would reveal what they were holding in their tiny beaks. His images used in this blog were taken with a handheld Canon R5 mirrorless camera fitted with a Canon RF 100-500 mm lens (f/4.5-7.1L IS USM) set to 500 mm.
Advances in image stabilisation combined with fast eye-tracking autofocus, a fast burst rate (20 images per second) and excellent low light performance assisted in the poor forest light. While there were plenty of blurred shots, many good shots were captured at ISO 3200 to 5000 and shutter speeds as low as 1/250 second. Extracting the cleanest, sharpest image was also helped with optimal RAW file processing in Canon Digital Photo Professional and advanced noise reduction software (Neat Image).
Cameras with similar performance to the Canon R5 are also available from other manufacturers, e.g. Nikon (Z8 and Z9 mirrorless) and Sony (Alpha 1 mirrorless). The use of a high pixel count camera (45 megapixel full-frame for the R5; similar or higher for the Nikon and Sony equivalents) greatly helps when using smaller, more compact lenses.
Combined, these factors enabled Glenn to capture the rapid feeding action of the birds in sufficient resolution and sharpness to show what they were holding in their beaks.
An unexpected diet
Tītitipounamu are almost entirely insectivorous. A long-term study in South Westland concluded that more than 99% of their diet was insects and other invertebrates. The only other food items identified were berries from two species of shrubs.
Several of the tītitipounamu images contributed to New Zealand Birds Online by other photographers show the birds holding identifiable food items, including several craneflies, a mayfly, a hoverfly, a caterpillar, a spider and a harvestman.
However, the images that Glenn captured in March 2023 showed that the birds appeared to be holding beech seeds – specifically the small, slender seeds of silver beech. We are unaware of any previous reports of tītitipounamu eating seeds.
Convincing the sceptics
While several forest ecologists agreed that the objects that the birds were holding looked like beech seeds, we decided that more evidence was needed to support our case. Fortunately, I was about to head into the field (on leave) and was able to gather several handfuls of gravel and leaf litter from under silver beech trees at the roadside at Kawatiri, north-east of Murchison.
These yielded about 30 seeds, from which Te Papa photographer Jean-Claude Stahl selected seeds that matched those shown in some of Glenn’s images.
By piercing the seeds on insect pins, which were held in position with plasticine, Jean-Claude was able to carefully orientate each seed until it had the same alignment as in Glenn’s images. The Te Papa images were taken with a Leica DMC 4500 camera mounted on a Leica Z6 Apo microscope.
Jean-Claude’s seed images were then reproduced to the same scale, and published as insets within Glenn’s images, with three examples shown here.
Glenn’s images show the birds squeezing a white, amorphous paste out of the seed cases. We believe the paste to be fat reserves (used to nourish the seeds’ cotyledons), and that the birds were swallowing the paste and discarding the hard seed cases.
A new food – or a new observation?
The ancestors of tītitipounamu and tawhai (southern beeches) have both inhabited the Zealandia subcontinent for tens of millions of years. Tītitipounamu may have had more than 80 million years to learn that beech seeds can provide an energy-rich food at a time of year (autumn) when insects are becoming scarce.
Glenn’s stunning images revealed a previously unrecognised food item for tītitipounamu. Maybe this has been occurring for millenia, and it took until 2023 for camera technology (and operator skill) to reveal what our eyes can’t see.
For more information
Pure, G.A. & Miskelly, C.M. 2023. Riflemen (tītitipounamu, Acanthisitta chloris: Acanthisittidae) eating seeds of silver beech (tawhai, Lophozonia menziesii: Nothofagaceae). Notornis 70: 139–142.
With thanks to Notornis for permission to reproduce images used in the above article.
One of my favourite birds. Superb photography.
Excellent work by all – fabulous images!