October 5, 2012 | 21
Some time back I started a series on the remarkable tubenosed seabirds known as the petrels (see below for links). Previous articles introduced the group as a whole before discussing one of the four major petrel clades, the gadfly-petrels or pterodromines. The time to finish this series is now well overdue, so here we look at the next major clade: the fulmarines. Look at the ‘consensus’ cladogram below to see how they fit with relation to the other petrel clades. Oh, it should be clear that this is a whistle-stop tour, or introduction, to these birds… there is so much more to say. [Images above by Snowmanradio, T. Müller and © Samuel Blanc]
Fulmarini includes the fulmars (Fulmarus) but also the Antarctic petrel Thalassoica antarctica, Snow petrel Pagodroma nivea, the Cape or Pintado petrel Daption capensis and Macronectes, the giant petrels. These are the robust-billed petrels. They also generally have stockier heads and necks than members of the other petrel groups. Some of them – the fulmars in particular – are superficially gull-like, and as a consequence authors of the 1800s and before sometimes regarded members of this group as “the section of Petrels most closely allied to the Laridae, and forming the connecting link between the two families” (Coues 1866, p. 26).
The genetic evidence grouping these species together is reasonably good. Amino acid distances suggest that they diverged from one another quite a long time ago, with the Pintado petrel lineage splitting off in the Late Oligocene and most of the other lineages (including even the fulmar subspecies) diverging during the Miocene. In discussing these divergence date estimates, Penhallurick & Wink (2004) did say, however, that this amino acid distance contradicts nucleotide distance data and “we suspect that … an error may have confounded the data here” (p. 139). How were these divergence estimates calibrated? Penhallurick & Wink (2004) assumed a molecular clock where 2% of nucleotide divergence occurred every million years – see their paper for the full discussion. I like Penhallurick and Wink’s paper, but I’m duty-bound to remind you that it was heavily criticised by Rheindt & Austin (2005).
The most familiar fulmarines are of course the two fulmars: the Northern or Arctic fulmar F. glacialis and the Antarctic, Silver-grey or Southern fulmar F. glacialoides. Northern fulmars come in both light and dark morphs, with the light one being superficially gull-like in colouration while the dark one is smoky-grey and looks superficially like a shearwater. The very darkest forms are known as dark-dark or double-dark. To confuse things further, intermediates between both forms occur. And three Northern fulmar subspecies have been recognised.
Fulmars (the name apparently comes from the Norse for ‘foul gull’) are unusual among petrels in being highly flexible in choice of nest site: they can and will nest in the mouths of burrows, but they much prefer steep cliffs. They’re also known to nest on flat ground, on scree slopes, on ruins and even on the roofs of buildings (Fisher & Lockley 1989). The Northern fulmar is one of several petrel species that has increased hugely in numbers within recent decades. From a dispersal point originally located in southern Iceland, fulmars have spread south and east over the past two centuries. In the British Isles the species was unique, as a breeding bird, to St Kilda in 1870, yet by the 1970s it occurred around the coasts of virtually the whole of Britain and Ireland. Why fulmars exploded in numbers remains uncertain. An increased availability of waste whale meat and fish products, warming conditions in the north-east Atlantic, and even the spread of a recently evolved population, better able than other fulmars to cope with warmer climes and more flexible in breeding behaviour, have been suggested as contributory factors.
Snow petrels, Antarctic petrels, Cape petrels
Somewhat distantly related to fulmars within Fulmarini is the completely white Snow petrel Pagodroma nivea, among the most distinctive of all petrels [adjacent photo by © Samuel Blanc]. Penhallurick & Wink (2004) recovered it as the sister-taxon to all other fulmarines. There are supposed to be two Snow petrel subspecies (the taxonomy of these two is extremely confusing and I will avoid it here), with P. n. confusa being larger (on average) and with a stouter bill. The suggestion has been made that it’s distinct enough to warrant recognition as a distinct species (Harrison 1988). Specialising on ice-edge prey, the long tail and low aspect ratio wings of the Snow petrel make it a particularly manoeuvrable bird, and of course it needs to be as it dodges around at the edges of icebergs and at small leads in pack ice.
Strong sexual size dimorphism – a variation of as much as 44% in body mass – is present in this species; proportionally one of the most pronounced degrees of dimorphism in any tubenose. Snow petrels are sometimes predated upon by South Polar skuas Stercorarius maccormicki, with the skuas eating adult birds as well as eggs and chicks (Barbraud 1999). Skuas also prey on Southern fulmars and on the next two species we’re going to look at. Incidentally, big fulmars are sometimes able to fend off big skuas: Mellor (2009) reported a case in which a Northern fulmar, observed eating a dead puffin on the sea surface, successfully deterred a Great skua S. skua that tried to claim (or reclaim) the carcass.
Another fulmarine of the Southern Oceans – the Antarctic petrel Thalassoica antarctica – is very different from the Snow petrel, having a short tail and short wings that have a high aspect ratio. [Plate above from New Zealand Electronic Text Centre.] These proportions assist in swift flight in strong wings, and also in pursuit diving (Spear & Ainley 1998). The Antarctic petrel also differs obviously from the Snow petrel in being strikingly marked, with dark brown upperparts and a white underside and broad white trailing edges on its wings. The tail is mostly white but with a black band at the tip. Antarctic petrels are famously gregarious breeders, with some of the larger colonies containing more than a million birds. They mostly breed on islands off the coast of Antarctica, but do use cliffs for breeding in some places.
A third fulmarine of the Southern Oceans – the Cape or Pintado petrel Daption capense – is superficially like the Antarctic petrel but is very obviously mottled and shorter-billed [adjacent photo by JJ Harrison]. It’s said to somewhat recall a sea-going pigeon in form and flight style, and indeed ‘Cape pigeon’ is another common name sometimes used for it. It has a characteristic erect and buoyant posture when feeding from the water surface but will also patter at the surface in storm-petrel fashion and also make shallow dives, both from a sitting start when it’s on the water surface and from a short distance above the water. Massive flocks sometimes follow ships, and the population as a whole is put at over 2 million.
Pagodroma, Thalassoica and Daption all seem to be outside a fulmarine clade that includes Fulmarus and Macronectes (Kennedy & Page 2002, Penhallurick & Wink 2004). The prominent dark markings of Thalassoica and Daption, and the sometimes dark brown pigmentation of Fulmarus and Macronectes, might suggest that dark, even bold, colouring was ancestral for Fulmarini. But, then, Pagodroma is white, and Fulmarus and Macronectes are often pale or even wholly white…
The giant petrels
Finally, we come to the Macronectes species (or subspecies): the giant petrels, sometimes called giant fulmars [adjacent image by Liam Quinn]. These are the most awesome fulmarines and among the most awesome of petrels. Their wingspans reach 2 m, meaning that they overlap in size with the smaller albatrosses. The massive, stout bill has a reddish tip in the Northern giant petrel M. halli while the Southern giant petrel M. giganteus exhibits a unique white morph. Within recent decades, the two have been considered separate species rather than subspecies but both are extremely similar genetically and some populations appear intermediate in characteristics. They hybridize where they occur together. In view of these factors, Penhallurick & Wink (2004) advocated reclassification as subspecies.
Giant petrels are especially interesting for lots of reasons. They are formidable predator and scavengers, feeding on krill, squid and fish but, more significantly, on other seabirds, including other petrels (prions, gadfly-petrels and fulmars are all among recorded prey species) and also on penguins. They’re unusual (perhaps unique) among petrels in feeding on land, and they use that powerful bill both to tear up carrion and grasp and dismember penguin and other seabird prey. Nelson (1980) says that a giant petrel “can tear a young or sickly albatross to pieces” (p. 62) and Cox (1978) described a case in which a giant petrel attacked, successfully drowned and then partially consumed a juvenile Black-browed albatross Thalassarche melanophrys at sea. While the precise numbers involved were hard to pin down, Hunter (1985) concluded that giant petrels were ecologically significant consumers of other seabirds.
All in all, the several fulmarine species are flexible, adaptable tubenosed seabirds that interact with other seabird species in interesting ways. The smaller ones scavenge, dive, patter on the sea-surface, sometimes form enormous squabbling flocks, and are sometimes predated upon by their larger cousins. The bigger ones – the giant petrels – are arch-predators and scavengers that routinely predate on other tubenoses and sometimes interact with other predatory seabirds, like great skuas. There are some great images online showing great skua – giant petrel interactions: look here and here. This image (below) is by Brocken Inaglory…
And for articles about other kinds of seabirds, see…
Refs – -
Barbraud, C. 1999. Subspecies-selective predation of snow petrels by skuas. Oikos 86, 275-282.
Coues, E. 1866. A critical review of the family Procellariidæ: Part III; embracing the Fulmareae. Proceedings of the Academy of Natural Sciences of Philadelphia 18, 25-33.
Fisher, J. & Lockley, R. M. 1989. Seabirds. Bloomsbury Books, London.
Harrison, P. 1988. Seabirds: an Identification Guide. Houghton Mifflin Company, Boston.
Hunter, S. 1985. The role of giant petrels in the Southern Ocean ecosytem. In Siegfried, W. R., Condy, P. R. & Laws, R. M. (eds) Antarctic Nutrient Cycles and Food Webs. Springer-Verlag (Berlin), pp. 534-542.
Kennedy, M. & Page R. D. M. 2002. Seabird supertrees: combining partial estimates of procellariform phylogeny. Auk 119, 88-108.
Nelson, B. 1980. Seabird: Their Biology and Ecology. Hamlyn, London.
Spear, L. B. & Ainley, D. G. 1998. Morphological differences relative to ecological segregation in petrels (family: Procellariidae) of the Southern Ocean and tropical Pacific. The Auk 115, 1017-1033.