151 Atkinson 1985 for examples), procellariiform popu- lations also typically spawn offshoots of a few hun- dred individuals on tiny offshore islands or stacks, and when invasions occur it is rare for populations to disappear entirely. Furthermore, a majority of petrel species arrive nocturnally on their breeding grounds, and burrow-nesting and extensive habi- tat gardening are the norm. Despite being susceptible to mammalian preda- tion, the procellariiforms are an ancient group that has survived comparatively unchanged since the earliest Cenozoic. Although procellariiform com- munities are dynamic over time (Warheit 2002), responding to environmental changes, mammalian invasions and the emergence of new islands, the taxa themselves have shown remarkable resilience. For example, the short-tailed albatross, Phoebastria albatrus, which is rare but still extant today, has managed to survive since at least the Pliocene (Olson and Rasmussen 2001) and move from the Atlantic, where it is now extinct (Olson and Hearty 2003), to the Pacific. Here I will attempt to deter- mine reasons for the group’s longevity, and discuss their ecosystem impacts and extinction drivers in the Holocene. 7.2 The earliest fossil record of procellariiformes 7.2.1 The Tertiary record (and earlier) Fossil evidence suggests that procellariiforms have survived comparatively unchanged since the 7.1 Introduction Procellariiformes are the order of tube-nosed sea- birds that includes the albatrosses, petrels, and shearwaters. Members of the order breed mainly on islands; individual species are often extremely widely distributed, with populations on many islands within many island groups, and fre- quently in different oceans. The order has a glo- bal distribution, and contains four extant families: Pelecanoididae (diving-petrels), Procellariidae (shearwaters, petrels, and fulmars), Diomedeidae (albatrosses), and Hydrobatidae (storm-petrels), together with either one or two extinct families. Species are generally either pelagic scavengers pri- marily taking squid and fish, or are planktivorous. As basal members of the Neoaves, the group has a physiologically restrained breeding system in which birds only produce a single egg, usually annually, with no relaying, do not have complex nest struc- tures, breed either at or below ground level, and generally have a tightly constrained breeding sea- son. These traits leave them open to predation by mammalian predators, and it is hypothesized that for this reason their breeding biology is character- ized by a number of behaviours that have evolved to reduce the effect of such predation. On islands where petrels are without predators they occur in huge numbers; indeed, one of the largest concen- trations of breeding animals in the world is a pet- rel colony (Reyes-Arriagada et al. 2007). Although these vast colonies are susceptible to the invasion of exotic mammals, and can disappear rapidly (see CHAPTER 7 Procellariform extinctions in the Holocene: threat processes and wider ecosystem-scale implications R. Paul Scofield 07-Turvey-Chap07.indd 151 07-Turvey-Chap07.indd 151 12/5/2008 12:21:47 PM 12/5/2008 12:21:47 PM