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Diving Petrel photograp
  Date: December 9, 2003
 
Div This picture was taken by Juan Pedro Paz-Soldan on a Pelagic from Callao on Oct 26, 2003. We had an unusual number of seen Diving-Petrels (over 50 total) and just as I recalled that this may well prove to be our highest count ever of Peruvian Diving-Petrel, I started wondering whether there may be other species involved. We repeated out loud caracters of Magellanic Diving-Petrel. Neck-collar and maybe somewhat more blackish plumage and soon enough we found birds that fitted to this description and Juan Pedro manage to get this shot. We were then quite convinced that this could be the first confirmed record of Magellanic Diving-Petrel from Peru. Later I noticed also that a particular bird on the water with a neck-collar looked smaller than good Peruvian Diving-Petrels seen later. This photo however shows a smudge in the collar and probably disqualifies the ID?

Gunnar Engblom
Kolibri Expeditions
kolibriexp@telefonica.net.pe
www.kolibriexpeditions.com

Postscript: Alvaro Jaramillo has later confirmed that it is a Peruvian Diving Petrel. See his new book Birds of Chile for a thorogh discussion regarding identification of Diving Petrels in the East Pacific.

Here are Alvaros comments:
Gunnar,

I checked out the photos on your website and I would call this bird a fine Peruvian Diving-Petrel, not a Magellanic. There are a few features that the books don´t usually mention that work for separating the two.
First of all size is a big one, while on measurements Magellanic averages only about 10% smaller, in actual bulk (mass) it is much, much smaller.
Comparing specimens this is really clear. In a group of Peruvians, a Magellanic would be unequivocally smaller. Mass is a cubic function so a 10% difference in linear measurements, creates a much larger difference in mass. Here are the rest:

1) Face pattern. Magellanic has a broad and obvious white collar that extends well up on the neck, it is highlighted by a thin and crisp dark spur that extends down on the sides of the breast. Peruvians do not show this spur, but show a broad dusky wash on the breast side like your bird does. The effect of the spur and white collar is that it sets off a dark cap on Magellanic, partially due to the distribution of black and white, but also because the interface between the two colours is sharper. Your bird lacks the capped look. It is normal, and even typical for Peruvian to show a pale or whitish area behind the ear coverts, but it is not the crisp whitish collar of Magellanic.

2) Bill size. Peruvian has a long and thick bill for a Diving Petrel, Magellanic a small bill. Your bird shows a typically large bill of a Peruvian.

3) Magellanic has pale grey or whitish flanks, not the dusky grey flanks of Peruvian. Your bird has the dusky grey flanks.

4) Magellanic has a whitish underwing, in fact the whitest underwing of any diving-petrel. Peruvian has a grey or dusky underwing. Your bird has the dusky typical of Peruvian.

5) The white trailing edge on the secondaries is broad and noticeable on Magellanic, Peruvian shows a narrow one. Beware that this is heavily affected by wear. Your bird shows almost no pale on the trailing edge of the secondaries.

I should note that our field guide to the Birds of Chile is finally out, and it deals with many of seabirds and species of southernmost Peru. I hope you folks find it useful! The diving-petrels are treated in there, the above points come from the book. Note that our plate of Peruvian shows more white on the secondaries than perhaps it should.

cheers

Alvaro

Alvaro Jaramillo
chucao@comcast.net
Montara, California
 
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