Whio Journal: Catching whio on Boyd Stream

The whio, or blue duck, appears on our $10 note and the wild rivers of the back country, and not many places in between. As such, few New Zealander’s know whio exist, and most will have never seen or heard one. With just 3,000 left in the wild, a partnership between Genesis and DOC called Whio Forever was struck in 2011 to protect and grow the population of this national taonga. In this ‘Whio Journal’ we wind the clock back to mid-August of 2019, in the South Island back country, joining the team for a whio catching and banding mission.

Jason Malham, DOC Science Technician:

The South Island back country doesn’t really start to feel the first stirrings of spring until late September, so a mid-August whio catching mission in the upper Wangapeka River promises chilly conditions. On the day, heavy cloud and snow showers delay our 09:00 helicopter pickup, and it’s not until midday that the weather clears and we are delivered to Boyd Hut in Kahurangi National Park. On the short flight we can see fresh snow to well below the bushline – it’s going to be cold!

After lunch and coffee at the hut we don the catching gear. For me it’s a bit of a palaver – merino long johns and top, fleece top, followed by calf-length neoprene socks, white-water kayaking dry pants and gravel guard gaiters, canyoneering boots, and finally a rain jacket. The dry pants take me ten minutes of struggling to put on as they have a very snug, water sealing rubber “cone” at the bottom of the legs. Rebecca and Ian (who are both wearing fly fishing waders) watch on bemusedly. Despite the cold conditions we know that we’ll be dry and mostly warm, providing we stay below chest-deep in the river.

So who are we and why are we planning to catch whio? I’m a science technician and manage a whio nesting success and adult survival study with my colleague, Biodiversity ranger, Rebecca Davies. Along with contractor Ian Newton, we are part of the Threats Unit, a Biodiversity Group science team based in Nelson. We’re catching and colour-banding new whio pairs in the south branch of the Wangapeka River in the Wangapeka/Fyfe Whio Security Site, so that we can monitor them during the breeding season. More on the study in a later blog post.

Why colour-bands, and not something more techy? In past years we deployed radio transmitters on female whio to allow us to locate their nests. However, we confirmed what others suspected – that radio-tagged female whio are less likely to breed than non-radio tagged birds. They end up losing weight and in a cold winter some succumbed to the harsh conditions. We ditched using transmitters at the start of the 2018/19 season and now rely on regular and thorough observations of colour-banded pairs to build a picture of the breeding season.

We have a 45 min walk up Boyd Stream to the starting point of the afternoon’s catching session. We strike it lucky today as the pair we intend catching are just 20 metres upstream from where the track descends back to the water after skirting a rugged gorge. The stream is less than 3 metres wide and not even knee-deep (hardly needed my fancy dry pants!) which will make setting up the net super easy.

The net is strung across a section of fast-flowing water between trees, the bottom line weighed down with rocks to ensure the whio pair don’t swim underneath. Now for the covert part of the mission. Hiding the gear out of sight, Rebecca and Ian disappear into the bush on opposite sides of the creek 10 metres upstream. I duck into the bush and sneak around the birds until I’m well upstream. Now I quietly walk out into the water and start down towards the whio pair, gently pushing them down the creek without alarm until they’re almost at the net. At this point we all rush at the birds who panic, while the fast current helps to trap them in the net. Being a new pair, never before caught, they are very naïve and easy to catch.

Processing a bird can take quite a while, so both are kept in cloth bags hung out of direct sunlight so as not to overheat them. Not that this is an issue today! I brought our baby bath thermometer from home this trip, just out of curiosity. The air temperature is a balmy 4°C and the water 4.4°C! It’s during this phase that we really feel the cold.

Processing involves weighing the whio and measuring its tarsus length (the area between the ‘knee’ and ‘ankle’ joint). Males are bigger and usually – but not always – heavier than females, but the tarsus measurement will confirm the sex as males are longer.

The next job is to colour-band the whio. Females are banded on the right leg, males on the left. We use coloured darvic plastic (unplasticized PVC) for the bands that are ‘welded’ shut using a solvent. When choosing colours we have to be careful – essentially we can’t have the same combination for any two whio on the same river catchment in case a bird dies, or a pair split up and couple up with another whio, which is more commonplace on densely-populated rivers.

On a nice warm sunny day the colour-bands set in minutes but in cold conditions we’ve got problems! We’ve done everything possible to help our cause, including warming the bands in gel hand-warmers, and choosing colours that seem to bind better than others in cold weather (blue, orange, green – don’t ask me why!). We then microchip them, much like you would your pet dog or cat, as a permanent non-threatening identification. Before microchips, metal identification bands were used on their legs but the metal could be worn down by grit, rocks and water, becoming sharp and causing injury. The colour-bands will be removed at the end of our study, another 2 – 3 years down the track. The last thing to do is name our whio pair. Whenever I’m at a loss I pull out a map and find some local features to name them after. We choose ‘Marino’ for the male after a range of mountains, and ‘Matiri’ for the female which refers to a nearby valley. Marino and Matiri swim off upstream into the dusk apparently none the worse for their experience. We on the other hand are freezing. A hot brew and nice cosy fire are only 45 minutes away…