Our last trip to Tawharanui wasn’t too successful in finding any Grey-faced petrels. Which is not surprising, given that it was the middle of the pre-breeding exodus, when all the breeding birds are feeding up before they have the long stint of incubation. Grey-faced petrels have an extremely long breeding season – they take around 55 days to incubate their eggs, a task shared by both parents, and then it’s another 118 days on average before the chick fledges. It takes a lot of energy and effort for the parents to continually feed the chick during this time – so the better condition they’re in a start of the season, the more likely they are to succeed.
This time, we’re into the incubation period, and our nest-box checking was very successful – lots of birds sitting on eggs! The number of Grey-faced petrels laying in nest-boxes at Tawharanui is increasing every year, as well as there being a few natural burrows. After we’d checked all the nest boxes, we headed out to the tip of the peninsula to wait for dark, and see how many birds we’d get this time.
It took a little while, and we killed time admiring the crescent moon and stunningly clear skies. But soon enough, there were the tell-tale calls in the air above us, responding to our vocal lure. For some reason, Grey-faced petrels (as well as other species) respond very strongly to ‘war-whooping’ – so we use these calls to attract them when we’re banding them. It’s most impressive during the pre-laying period when the birds are prospecting for mates and burrows, when there are the most birds around at the colonies.
Success! We didn’t have a rush of birds, but over the course of the two hours we caught seven birds – four of which were already banded, and three new birds. There were quite a few others circling in the air above us, but they didn’t land while were there.
As well as banding the new birds and recording the band numbers of the others, we took weight measurements to check on the condition of the birds. Because we’re interrupting their lives to band them, it’s good to try and maximise the amount of data we can get in one go – and weight is a good indicator of physical condition, as well as being a relatively easy thing to measure.
I had a bit of time on my hands, so I spent a bit of time with the birds after we’d released them to get some photographs. It’s something I haven’t had time to do during my own field sessions because my hands are full (of birds), so it was nice to have a bit of space to get some images. Trying to get an angle that hid the Twink marks on their foreheads was a little challenging!
Aren’t they gorgeous though?
The stars were pretty fantastic too. One of my favourite things about visiting Tawharanui is escaping the haze of the city and being able to see up into clear skies at night – it’s one of the things I really miss.
Til next month, Tawharanui! Over the coming weeks I’m going to be very busy with my own fieldwork, but I’m hoping to still get blogs out as normal. You can tell by the timing of today’s post that I nearly forgot that I didn’t have anything scheduled… I’ll try and get a few ready in advance today!