Blog by Michelle Jones, Gough Field Assistant
Despite surface nesting seabirds, like albatrosses and giant petrels often stealing the limelight, the vast majority of seabirds that breed on Gough nest underground. These birds are mostly active at night, so we see them return to the Island in spectacular swarms around sunset, and their beautifully eerie calls fill the Gough night sky. It is amazing how faithful they are to their burrow, with birds returning year after year to the same tiny patch of land. They spend time each year refurbishing their burrow, which can reach up to 2.5 metres in length!
For anyone who has been to Gough, they will know that it is difficult to walk without regularly falling over, not only due to the dense vegetation in the lowlands, but also due to the high density of burrows. If you are not looking at your feet, you can easily fall flat on your face after being tripped up by a burrow entrance!
Of the 14 species of burrowing petrels that breed on Gough we have two long-term monitoring projects, which look at the density, occupancy and breeding success of Great shearwaters (summer breeders) and Atlantic petrels (winter breeders). For breeding success monitoring we check a subset of burrows at incubation, hatching and fledging to determine how many of the active nests fledge a chick.
You may be wondering how we monitor these birds that live underground in burrows with long tunnels…
To monitor the nests, we use a burrow camera. This is a small handheld camera, fitted with a torch that is manoeuvred into the burrow. The camera is attached to a long semi-rigid cable, to a screen that we can view outside the burrow. Burrows typically have a long tunnel, which opens into a larger burrow chamber. There is depression in the chamber where the bird will lay their egg. When we look inside the burrow, we check to see if the burrow chamber is active (a bird sitting on an egg/chick) or empty. Sometimes this puts us in interesting yoga-like poses as some burrows have very convoluted entrances and result in the (what we could call) the ‘Downward Bird’ pose. These projects are an exciting opportunity to look into the homes of birds that are not seen above ground.
Because Atlantic petrels breed in winter when mice have little other food sources, they are one of the species most impacted by mouse predation. Breeding success of the monitored burrows has been as low as 20%, which has led to the species being classified as Endangered by the IUCN. Thankfully, due to the efforts of the Gough Island Restoration, 2019 should be the last year that this species will suffer extremely low breeding success due to mice.
We all look forward to seeing how nesting success improves for these species on a mouse-free island!
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Acknowledgement
The Gough Island Restoration Programme is being carried out by the RSPB in partnership with Tristan da Cunha , BirdLife South Africa and the Department of Environmental Affairs in South Africa and Island Conservation . The programme is part-funded by the RSPB, the UK Government, the National Fish and Wildlife Foundation and other generous individuals and organisations.