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Updated in March 2011 

relating to a bird during the FOCUS ON NATURE TOUR IN CHILE
in November/December 2009

"What was "A Mystery Storm-Petrel", now said to be a new species

During a ferry-boat ride to Chiloe Island, on December 1, 2009, as part of the FONT Nov/Dec '09 Tour in Chile, some storm-petrels were noticed with more extensive white than expected on their vents/bellies.

What we did not know at the time was that earlier that same year, another group of birders (from Ireland: Seamus Enright, Michael O'Keefe & friends), in waters in much that same area, also observed such similar storm-petrels. 

Now, more recently, this news: 

In February 2011, during a five-person multi-national expedition led by British seabird expert Peter Harrison, 12 of the "mystery storm petrels" were captured at sea near Puerto Montt, Chile. By so doing, that team has been able to confirm the existence of a new species.

According to Harrison, "These birds appear to be a new species, as they are so different from any other storm petrels we know."  There are 22 known species of storm petrels worldwide. 

The following narrative, from the blog "Birding Abroad", relates more of the latest news:

Recent sightings of unidentified storm petrels in Seno Reloncavi, south of Puerto Montt, Chile, have been confirmed as a new species, as recently published in "Dutch Birding" (O'Keefe et al 2010).  
A team of biologists led (as noted above) by British seabird expert Peter Harrison, has just completed an expedition to that area of Chile.
The expedition followed Harrison's earlier examination of two skins of an Oceanites sp. housed in the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina.
Those two skins had been described by Pearman as the first Argentinian records of Elliot's Storm Petrel, Oceanites gracilis galapogoensis (Pearman 2000). 
On examining the specimens, Harrison concluded that the two originally collected at El Bolson, Rio Negro province, Argentina, in February 1972 and November 1983 represented a hitherto undescribed taxon and were probably the mysterious unidentified storm petrels of Puerto Montt, Chile, which is just 70 kilometers west of El Bolson.

Two members of the team of biologists, Chris Gaskin and Karen Baird from New Zealand, were both involved in at-sea captures and searches for the breeding location of the recently rediscovered New Zealand Storm Petrel (Gaskin & Baird 2005, Stephenson et al. 2008).

The Chilean expedition spent 4 days at sea in the Seno Reloncavi area, where they made use of chum or berley (fish scraps) to attract seabirds within range of the specially designed net-guns. These were critical to the success of the expedition and were developed in New Zealand for the capture of the New Zealand Storm Petrel.

Over the four days at sea, over 1,500 sightings of the new Oceanites species were recorded. To enable the scientific description of the new species, the 12 birds (as noted above) were captured for the collection of biometric data and samples of blood and feathers taken for genetic work.

The new species would appear to be most closely related to the Elliot's Storm Petrel, Oceanites gracilis. But in appearance it is intermediate between the Wilson's Storm Petrel and the New Zealand Storm Petrel. It shows a distinctive pale upper wing crescent and a prominent white bar across the underwing coverts. Unlike typical Elliot's Storm Petrels, the white feathering in the ventral area is much more subdued and restricted and does not extend toward the upper breast. The wing measurements are also very different and show no overlap with the mainland Elliot's Storm Petrel.

The expedition team estimates a population of 5,000 to 10,000 birds in the Seno Reloncavi area, where the new taxon appears to be the most abundant of the resident seabirds, with flocks of several hundred individuals at chum slicks.
The timing of the expedition appears to have coincided with the fledging period as juveniles were among the captured birds, suggesting that breeding occurs in the Seno Reloncavi area, possibly beginning in November. 
A wider search of the Seno Relanocavi and Golfo de Ancud area needs to be undertaken in both summer and winter. 
Further analysis of feather and blood samples is expected to confirm this discovery and a full scientific publication is in preparation by the expedition team. 

Beneath the photos below is what was written here last year (in 2010) and relating to the "Dutch Birding" article mentioned above. 

These photos were taken in nearly the same Chilean waters
a few months before our Nov/Dec '09 FONT tour,
taken in February 2009 by Michael O'Keeffe

This "mystery storm-petrel" was seen during the FONT Chile tour
on December 1, 2009 from the ferry to Chiloe Island.

What follows, regarding these storm-petrels in southern Chilean waters, is from a paper that was authored in 2009, by Jim Dowdall, Seamus Enright, Kieran Fahy, Jeff Gilligan, Gerard Lillie, and Michael O'Keeffe, for DUTCH BIRDING (published in 2010):     

The most striking feature of the birds was the extent of white in the plumage underneath, suggesting initially one of the Fregetta storm-petrels. However, other features seemed to rule out that option, including the extent of dark on the flanks and the prominent carpal bar. 
The birds appeared to have characteristics making them Oceanites storm-petrels, similar but perhaps slightly stockier of the chilensis Wilson's Storm Petrel. But the whitish upper-wing and under-wing panels appeared more striking than chilensis. The white on the rump appeared to wrap completely around the vent/lower belly, although from photos it is hard to rule out the presence of perhaps some dark feathering on the sides and the center of the vent.

So, some questions:

Why have these birds apparently gone undocumented until now?

Other visiting birders, in recent years, in the coastal waters south of Puerto Montt, and from the ferry crossing to/from Chiloe Island, have noted similar birds.
For example, Peter Harrison first encountered them while working onboard the tour vessel M.V. Linblad Explorer, out of Puerto Montt in 1983 and 1984. Harrison also saw the birds again in later years. On two occasions, he remarked that he "was lucky enough to have one land on the deck during the night and was able to give them careful scrutiny. Using his only reference (Murphy, 1936), and based on measurements he obtained, Harrison concluded the birds to be chilensis.

The enigmatic chilensis race of the Wilson's Storm Petrel has had a checkered history. Robert Cushman Murphy inthe "Oceanic Birds of South America" (1936) described how the taxa Oceanites oceanicus chilensis was inadvertently first published nomen nudum by W.B. Alexander in "Birds of the Oceans" (1928). 
The taxa was later described in detail by Murphy (1936) and referred to as the "Fuegian Petrel", a new subspecies of the Wilson's Storm Petrel.
Subsequent to that, and for reasons not quite understood, the taxa was "dropped" as a race of the Wilson's. Until very recently, only two races of Wilson's Storm Petrels, oceanicus and exasperates, were recognized in the literature, including by Harrison (1983, and in subsequent editions).
Interestingly, in relation to the Wilson's Storm Petrel, Harrison has noted that "Cape Horn birds have pale vents", again apparently relating to chilensis, noting also some pale mottling on the lower belly.
Onley and Scofield (2007) have recently re-established chilensis as a race of the Wilson's Storm Petrel.

So, a conclusion could be that the storm-petrels, with the white on their vents/bellies in the Chilean waters south of Puerto Montt were undocumented in part due to the lack of understanding of the form chilensis also occurring in those waters, and probably most importantly, they were undocumented because simply not many people were aware of them.       

The storm petrels, with the white apparently more extensive than chilensis, have been observed south of Puerto Montt, in the channel north of Chiloe island (where they were seen during the 2009 FONT tour), and also in the Gulf of Penas, approximately 500 kilometers south of Puerto Montt. It is therefore suggested that these birds are relatively localized and sedentary,

Could these birds be a new species?       

The most conservative explanation is that they are simply a previously un-described plumage or morph of one of the species already known from the region.
The combination of plumage features perhaps most closely matches the Elliot's Storm Petrel. But generally that species generally has much more white on the upper belly and generally more dark feathering on the vent, creating a distinctive divide between the white belly and the rump.
Also, the waters south of Puerto Montt seem surely to be too far removed, so far south of the range of the Elliot's, which is a warm-water species, and thus not apt to occur to cold southern Chilean waters.

Very interestingly, in 2000, two specimens of storm petrels were taken from El Bolson, in the province of Rio Negro, in southern (Patagonian) Argentina. They were assigned to the northerly race of the Elliot's Storm Petrel, galapogoensis. They currently represent the first (and the only) records of Elliot's Storm Petrel for Argentina (where, of course, they would be from the South Atlantic Coast.)
The wing measurements of the "white-bellied" storm petrels from south of Puerto Montt in Chile indicate the birds to be larger than gracilis Elliot's, and within the range of chilensis or galapogoensis (with however, as noted, the plumage features not matching either of those taxa). 
The El Bolson (Argentina) birds are only marginally longer winged than the Puerto Montt birds just noted as studied by Harrison in the hand.
It could possibly be that the El Bolson specimens are examples of the unidentified "white-bellied" Puerto Montt storm petrels, and not Elliot's. 

Returning again to the chilensis race of the Wilson's Storm Petrel, some observers are of the opinion that it may in actuality be closer to the Elliot's than to the Wilson's. 
With the "white bellied " storm petrels south of Puerto Montt also requiring analysis, this may be a good time to re-think, and thus give further study, the entire storm-petrel taxa in that region of southern Chile.

It is hard not to draw certain parallels between this story of storm petrels in southern Chile and that of the New Zealand Storm Petrel, Oceanites maorianus, that was recently, in 2003, found to be alive and well. 
Indeed, the "white-bellied" Puerto Montt/Chiloe Island birds share a startling similarity with that rare species that lives on the far-opposite side of the South Pacific.  

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