White-faced Storm-petrel

Due to the inexplicable failure of any of the recent white-winged gulls to pay a visit to Topsham I find myself with a month since my last post and no local birds to write about. Time to dig into my folder of seabird photos and look at one of the most charismatic of West Palearctic birds.

Some birds have the looks and the moves. White-faced Storm-petrel* would be a great-looking seabird even if all it did was fly around. But when it does it's thing it has to be seen to be believed. In 2011 I saw several from a small boat a few miles off Madeira (courtesy of the highly recommended Madeira Windbirds - thanks Caterina and Hugo). They were easily picked out at distance, looking just like bouncing white balls as they hunted down the scent of the fish scraps and oil. Closer, they floated like tiny hang gliders coming in to land, wings spread and flat, hardly flapping; their ridiculously long legs and toes dangling or springing from the surface in huge leaps. Photo opportunities were excellent, even I got some decent shots.

I've been researching this species for illustrations for the forthcoming 'Tubenose Handbook' (Shirihai & Bretagnolle, in prep.). As well as studying the species at sea, I've examined hundreds of photos and all the specimens at the BMNH at Tring. First some taxonomy: genus Pelagodroma, just one species marina. Part of the family Oceanitidae which is basically a Southern Oceans group and appears to be more closely related to the Albatrosses than to the northern Storm-petrels of the family Hydrobatidae. Some species of tubenoses have a small range, some are widely spread. Pelagodroma is one of the latter, breeding in both the North and South Atlantic and the South Pacific. Here are the currently recognised subspecies (from north west to south east):

hypoleuca - breeds Selvagens Islands, Canary Islands
eadesi - breeds Cape Verde Islands
nominate marina - breeds South Atlantic at Tristan da Cunha and Gough
maoriana - breeds islands off New Zealand, Auckland Islands and Chatham Islands
dulciae - breeds islands off southern coast of Australia
albiclunis - breeds Kermadec Islands.

Since the other members of Oceanitidae are basically southern hemisphere breeders, it would seem likely that Pelgodroma originated in the south and is a relatively recent colonist of the North Atlantic, but it's curious that the North Atlantic taxa resemble dulciae and albiclunis more than marina from the South Atlantic - environmental factors maybe? In fact for a species with such a wide range there isn't a lot of variation between taxa; it has been suggested that differences are so slight that subspecies eadesi should be merged with hypoleuca and that maoriana is best lumped with nominate marina. Having examined the small sample held at Tring I find it hard to disagree - in terms of appearance at least. So what are the differences between the subspecies? They seem to fall into three groups:

1. North Atlantic - eadesi and hypoleuca; long-billed, long-legged with shallow tail fork; slightly paler above with more white on neck sides and smaller breast side patches.

2. Australia and Kermadecs - dulciae and albiclunis; long-billed, short to medium length tarsus with shallow tail fork; plumage similar to group 1 although albiclunis often shows all white rump and upper tail coverts.

3. South Atlantic and New Zealand - marina and maoriana; short-billed, short tarsus and often deep tail fork; slightly darker above with less white on neck sides and breast side patches large and sometimes forming breast band.

The difference in bill length is particularly noticeable - typical maoriana and eadesi below. Why do warm water populations have longer bills? And why do colder water breeders show shorter legs and toes but longer, more forked tails?

 The two forms dulciae and albiclunis are extremely similar and geographically close, it has been suggested that the variably white-rumped albiclunis may be just worn dulciae (Marchant & Higgins 1990, Imber 1984).

And now for some speculation: as far as I know, there has been no research into the genetics of Pelagodroma; for example, what are relationships between the different populations and when did they diverge? I'd also be curious to know if and how the calls differ. Given the recent tendency of tubenoses to throw up cryptic species - e.g. proposed splits in the Band-rumped/Madeiran Storm-petrel and the Leach's Storm-petrel complexes - I wouldn't be surprised if Pelagodroma is equally interesting.

* some people get upset over English names for birds. I prefer clarity to tradition. Pelagodroma marina used to be known as White-faced Petrel (or Frigate Petrel). 'Storm-petrel' conveniently distinguishes these birds from the generally much larger petrels.  Neither name has any taxonomic significance, 'storm-petrel' includes all the smaller species but actually covers two quite distinct families within the Procellariiformes; 'petrel' is a general term for those small to mid-sized tubenoses that aren't obviously shearwaters - although some 'petrels' appear to be more related to shearwaters than they are to other petrels.

References

Imber, M.J. 1984. Migration of White-faced Storm-petrels Pelagodroma marina in the South Pacific and the status of the Kermadec subspecies. Emu 84.: 32-35.
Marchant, S. & P.J. Higgins (eds) 1990. Handbook of Australian, New Zealand and Antarctic Birds. Volume 1: Ratites to Ducks. Oxford University Press, Melbourne
Shirihai, H. & Bretagnolle, V. Albatrosses, Petrels and Shearwaters of the World.  a Handbook to their Taxonomy, Identification, Ecology and Conservation. A&C Black/Christopher Helm, London (in prep.)