Black Petrel Monitoring - Great Barrier Island

Possibly among the more laid back in their quest to finish Te Araroa, we knew that we had time on our side (hindsights a wonderful thing...) and so were in no rush to crack on and finish. This helped us to remain flexible to opportunities as they arose, and so when we had the chance to spend the month of January on Great Barrier Island helping to carry out surveys and monitoring of the black petrel populations there, we naturally jumped at the chance. Shortly after spending a few days visiting Mt Taranaki, and an incredibly indulgent Christmas in Palmerston North thanks to the kindness of trail angels John and Gail, we were soon heading back north to leave all those luxuries behind.

The mountainous forest habitat of Great Barrier Island, throughout which we would be in search of black petrels.

Great Barrier Island is an inhabited island which is a relatively short 50 minute flight from Auckland. It's home to about 1000 residents, a popular spot for tourists, and it's forested mountains are where you can experience the amazing black petresls. The petrels themselves are members of the tube-nose family and are burrow nesting seabirds, with the majority of nests being found around Great Barriers highest point on Hirakimata (Mt Hobson). In order to monitor the more than 450 study burrows, we would be living in the bush for the next 35 days and heading out daily to establish who is living where, as well as attempting to find new burrows in the more inaccessible areas of the bush. Cue 35 days of soaring temperatures, bush bashing through dense bush, and a deepening understanding of how vague topographic maps in New Zealand really are.

Carrying out the burrow checks for the study sites was a real highlight. Following Wildlife Management International Ltd's Biz Bell illustrated just how well you get to know these birds and their burrows after researching them for 25 years. “Burrow 137, yeah he's a psycho, we'll let Ed get this one.”, and sure enough upon reaching into the burrow, (with a gloved hand I will emphasise) to extract the bird, they would kick, scratch, and generally make their opinion known. Not all the birds are like this however, and you do get the nice relaxed calm individuals. The ones who I can only assume are familiar with the process and happily wait for us to put them back. It helps to have people of varying proportions on the team as well. I found out that my longer arms meant I could reach some birds where others couldn't, and Lydia found that her smaller size meant she was ideal to be sacrificed in pursuit of those birds who made their homes in caverns and hollow logs too small for myself.

A calm black petrel waits patiently to be returned to its burrow after having its band number recorded.

It wouldn't just be working through the day either, as many of the breeding pairs would swap roles under the cover of darkness. The parent who has been incubating the egg for several days will swap with their partner when they return from feeding at sea, and at night you could easily see this exchange taking place. The returning adults would crash land through the forest canopy onto the floor below, and those heading out to sea would seek out a high point to take off from. The wooden summit platform in this case being the perfect site to set out to sea, so we would sit and wait, listening for the sound of claws on stairs as they climbed their way to the launch pad. One person with quick enough reactions could catch the individual, have their band recorded or assigned to them if they didn't already have one, and then be released again to carry on their business.

Banding a black petrel
A black petrel caught at night on the summit has a new band secured before it takes flight.

Besides helping with the monitoring of the study burrows and banding birds in premium habitat, we were set the task of finding new burrows in the dense vegetation of lower quality habitat. Randomly generated points on a map would become public enemy number one, navigating our way with map and compass and double checking our accuracy with a GPS. Our personal record for slow progress topped out at about 250 metres an hour through a seemingly impenetrable wall of scrub. Bush bashing for about 5 hours across a mountainous ridgeline to hit an impassable sheer cliff would also be a fond memory from our time in search of black petrels. As hard as this work was, we had to remind ourselves that we were exploring areas of the forest that hadn't seen humans in about 100 years, when the kauri loggers would have felled the immense kauri trees for their timber.

Transects are measured out along a compass bearing, no matter how dense the bush gets.

This hard work however was always worth it when a burrow was found, and after a while you develop a sense for when birds will be in an area. You see signs of their activity such as clear ground from their digging and tidying of their homes, flattened moss from where males perch at night outside their burrows calling to attract a mate, and the obvious giveaway being poo. But there's more to poo than you might first think. Green poo suggests its a bird who is incubating an egg, not coming out to relieve themselves regularly and therefore resulting in a more concentrated, green dropping. White poo is more likely to be a non-breeder as they come and go each day to feed, pooing as they do so, leaving a much brighter white splat outside their home. The more you know!

The hardest days came when spending a day in an area that screamed with potential for burrows, only to find burrows that had been destroyed and predated by non-native species such as pigs and rats. While on occasion we would find sign of rat predation such as broken egg shells or a predated chick, this one particular burrow was possibly the most shocking discovery we made. Lydia had noticed a clear area beyond a rise in the ground, indicating a bird may well be tidying up a burrow entrance that was out of sight. I went to investigate and found a perfect burrow entrance. I reached in to be pleasantly pecked by the occupier, with careful hands I could also feel an egg. No further action needed, we can mark the burrow down as an active breeding burrow and move on. Taking a couple of steps around the side however revealed a much more horrific story.

The entrance to this burrow is actually to the right. This hole is the work of feral pigs, which dig up and predate the birds.

Pigs are not native to New Zealand, and as such the native species here aren't really that well prepared to cope with them. The pigs roam in many areas of bush throughout New Zealand and are a staple food for many kiwis who hunt them to provide meat for their families, a problem arises however when their populations are left unmonitored and they disperse into areas that are ecologically sensitive to their presence. Their acute sense of smell and impressive strength mean they are skilled at digging and breaking through tree roots in order to reach whatever they've found, which sadly in this case is the black petrels. In the pigs efforts to break into this burrow, it has broken through roots as thick as my wrist and completely excavated the soil. A search of the area revealed yet more saddening news. The feathers and bones of an adult bird were strewn about nearby and, though we can't be certain, there is a good chance that the predated bird was the partner of the one we had found.

What this means in the long-term for this bird, is that it will be unable to rear a chick this season. Without a partner to swap roles with, the adult will eventually have to abandon the nest to feed therefore leaving the egg without incubation resulting in a failure of the embryo. While this was a saddening way to end our time living and working in Great Barrier's mountainous forest, we were still able to take away many happy memories and encounters with these charming seabirds. The data we had helped to collect will help to build upon ongoing research, and inform conservation action into the future in order to help protect these incredible birds. For us, it was time to return to the mainland and complete our final leg of the North Island.