Breeding

The following summary based on information in Plant (1989) and M.J. Imber (reported in Marchant and Higgins 1990) working on the Chathams, and Jouventin et al. (1985) working on the Crozets, and summarized by Brooke (2004). There is no detailed information on the breeding of Gray-backed Storm-Petrel from islands near South America.

Gray-backed Storm-Petrel is strictly nocturnal at colonies, which are usually coastal. Makes burrows in vegetation such as tussock grass or flax, rather than underground, that can be up to 50 cm long and 7 cm in diameter.

Colonies are active throughout the year, but the primary nesting period is August-April. Date of return varies with colony location, but is usually centered around October. Main return to breeding sites Oct/Nov, with most activity at colonies between Aug–Apr, pre-laying exodus of c. 14 days and protracted egg-laying period (at least on Chatham Is) from Sept to end of Dec 4 West, J.A. and Nilsson, R.J. (1994). Habitat use and burrow densities of burrow-nesting seabirds on South East Island, Chatham Islands, New Zealand. Notornis. 41(Suppl.): 27–37. Close , more concentrated on Crozets (15–29 Dec) 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close . Prelaying exodus is approximately 14 days.

Assumed to be monogamous and to form long-term pair-bonds 2 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close . Forms loose colonies, sometimes mixed with other species of tubenose 4 West, J.A. and Nilsson, R.J. (1994). Habitat use and burrow densities of burrow-nesting seabirds on South East Island, Chatham Islands, New Zealand. Notornis. 41(Suppl.): 27–37. Close ; nest is virtually unlined burrow, tunnel in vegetation (Carex chathamica, Muehlenbeckia australis and Poa spp. on Chathams) 4 West, J.A. and Nilsson, R.J. (1994). Habitat use and burrow densities of burrow-nesting seabirds on South East Island, Chatham Islands, New Zealand. Notornis. 41(Suppl.): 27–37. Close or crevice in rocks, usually above ground, up to 50 cm long and 7 cm in diameter 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close .

Clutch single white egg spotted at broad end 2 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close . Egg-laying protracted on Chathams, occupying from late September to the end of the year. On the Crozets, laying period concentrated in the period 15-29 December. On the Chatham Islands, egg size is 29.2-33.0 mm x 22.0-23.9 mm, and the weight is between 6.8-9.9 g (n = 18). On the Crozets, egg size 31.6-37.5 mm x 22.7-25.7 mm, and the weight is 8.5-10.0 g (n = 8), which is approximately 28.1% of the female's weight 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ; incubation estimated c. 45 days with stints of 1–3 days; chicks  have dark grey down, brooded no more than 24 hours and then fed every 1·6 days 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ; fledging mostly in late Mar/Apr when c. 50 days old, though reaches adult weight after c. 17 days and achieves peak mass in excess of 50 g 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close . Incubation shifts average 1.9 days on the Chathams, followed by desertion periods of approximately 2.7 days. There is a possibility that these desertion periods are partially caused by researcher disturbance.

The newly hatched chick is brooded for no more than 24 hours (Despin et al. 1972). Chicks are fed every 1.6 days, reaching adult weight after about 17 days. Peak weight exceeds 50 grams (Despin et al. 1972). Fledging occurs at about 50 days (Heather and Robertson 1997). In the Crozets, birds fledge in late March or very early April (Despin et al. 1972).

Breeding success unquantified 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close , although rats, cats and perhaps also skuas (Catharacta) 11 Hemmings, A.D. (1990). Winter territory occupation and behavior of Great Skuas at the Chatham Islands, New Zealand. Emu. 90(2): 108–113. Close predate adults, chicks and eggs on some islands, and substantial predation of adults by Short-eared Owls (Asio flammeus) is reported on Falkland Is 2 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close .