Where they co-exist at the same location, Northern Giant Petrels breed approximately six weeks before Southern Giant Petrels (Hunter 1987, De Bruyn et al. 2007, Brown et al. 2015), though low levels of hybridisation occur on Macquarie Island and at South Georgia (Brown et al. 2015, and R. Alderman pers. comm.). Birds feed on penguin and pinniped carrion, cephalopods, krill, offal, discarded fish and refuse from ships, often feeding near trawlers and longliners (Hunter and Brooke 1982, Hunter 1983). Males and females exhibit clearly defined spatial segregation in foraging ranges (Hunter 1983, Gonzalez-Solis et al. 2000, Becker et al. 2002, Gonzalez-Solis and Croxall 2005, Thiers et al. 2014). During the breeding season, males exploit scavenging opportunities in and around seal and penguin colonies and are coastal in distribution, whereas females are much more dependent on pelagic resources (Quintana and Dell'Arciprete 2002, Patterson and Fraser 2003, BirdLife International 2004). There is significant sexual dimorphism, with female mass approximately 80% that of males (Gonzalez-Solis 2004). Ringing recoveries indicate juveniles forage more widely than adults (Hunter 1984a). At some sites, its less colonial breeding habit may make it less sensitive to human disturbance than Southern Giant Petrel, though their degree of coloniality does not differ on South Georgia (Georgias del Sur), the largest breeding colony (R. A. Phillips in litt. 2008). On the Chatham Islands, regurgitations from the birds on the Forty-Fours indicate a reliance on natural food sources (esp. Gnathophausia ingens) rather than carrion - there being no penguin colonies in the Chatham Islands (C. J. R. Robertson in litt. 2008). Average age of first breeding is c.10 years, and mean adult annual survival at South Georgia is 90% (Hunter 1984a).

Macronectes halli breeds at South Georgia (Georgias del Sur), Prince Edward Islands (South Africa), Crozet and Kerguelen Islands (French Southern Territories), Macquarie Island (Australia), Auckland, Campbell, Antipodes and Chatham Islands and, historically, on islets off Stewart Island (New Zealand). The world population in the 1980s was estimated at c.8,600 pairs (Hunter 1985). A more recent estimate is 11,800 pairs (ACAP 2010). The population of Northern Giant Petrel has shown both decreases and dramatic increases across their breeding range (ACAP 2010). Increasing trends may be partly attributed to better monitoring, but also probably reflects greater availability of carrion from expanding populations of fur seals Arctocephalus gazella and A. tropicalis, increased waste from commercial fishing operations (Patterson et al. 2008), and use of measures to reduce seabird bycatch around some breeding colonies, such as South Georgia (Georgias del Sur).

Conservation Actions Underway
CMS Appendix II and ACAP Annex 1.

Conservation Actions Proposed
Conduct surveys of major breeding sites. Continue monitoring. Minimise disturbance at breeding sites. Research movements and migration. Promote adoption of best-practice mitigation measures in all fisheries within its range, including via intergovernmental mechanisms such as ACAP, FAO and Regional Fisheries Management Organisations.