Leica team member Steve Howell is back recently from a ten-day pelagic trip off northwest Mexico, where he saw plenty of ‘Leach’s Storm-Petrels’ – including the enigmatic Ainley’s Storm-Petrel, endemic as a breeder to Mexico’s Guadalupe Island (about 170 miles west of the Baja California Peninsula), described as new to science as recently as 1980, and never before photographed at sea! Here’s the story…

Ainley’s Storm-Petrel? Huh, what’s that? OK, here’s a synopsis of taxonomy to put the story in context. (Don’t worry, it’s short!) In 1980, marine scientist David Ainley described the winter-breeding ‘Leach’s Storm-Petrels’ on Mexico’s Guadalupe Island as a new taxon, cheimomnestes(meaning ‘winter suitor’). He analyzed morphology, plumage, and vocalizations and pointed out that both Guadalupe breeding populations of ‘Leach’s’ (winter-breeding cheimomnestes and summer-breeding socorroensis) were so distinct from all other populations of Leach’s (from the North Atlantic, and from Alaska south to Mexico) that “if they met it is questionable that interbreeding would occur” (Ainley 1980:849). A victim of that era’s taxonomic vogue, however, Ainley treated cheimomnestes and socorroensis as subspecies of Leach’s, comparing their situation to taxa treated at that time as subspecies of ‘Soft-plumaged Petrel.’ The latter, however, have long since been split as full species—the famed Fea’s and Zino’s Petrels—but the Leach’s Storm-Petrel complex has continued to languish in a sea of neglect.

In 2012, in Petrels, Albatrosses, and Storm-Petrels of North America I treated both Guadalupe taxa as full species: Townsend’s Storm-Petrel (socorroensis) and Ainley’s Storm-Petrel (named in honor of the scientists who described them), a realistic conclusion that best fits with the data and is comparable to other recent tubenose taxonomy. Apparently, a genetic analysis was even done years ago and supports this split, but the results remain unpublished; thus, despite peer-reviewed morphological and vocal data published in their own magazine Auk, the AOU has not split these distinct taxa (a classic case of Split or Get Off the Pot).

Taxonomy is not an academic science, however. It is critical to understanding and protecting biodiversity. But sadly, many professional taxonomists seem to care more about their egos and careers and following bureaucratic protocols than about helping preserve the world around them. As E. O. Wilson (2014:125) notes, the rate of diagnosing and naming of new species “is a disgrace of the biological sciences.” The failure to split species for which published data exist is an even greater travesty—basically, ornithologists fiddle while Rome burns. The breeding populations of Ainley’s and Townsend’s Storm-Petrels are each estimated at only a few thousand pairs, restricted to a few rocky islets off the main island of Guadalupe. Perhaps they will be ‘officially’ split only when they have become extinct, as has already happened (thanks to non-native predators) with Guadalupe Storm-Petrel and Guadalupe Caracara from the selfsame Mexican island.

OK, back to the story. Seeing Ainley’s Storm-Petrel was one of the main goals of our trip, but we did not chum near the island in late afternoon (probably our best chance for seeing birds at sea) and our fish-oil slicks farther offshore produced lots of ‘Leach’s’ but no candidates for Ainley’s. However, anchored off the south end of Guadalupe at night we saw storm-petrels in the lights of the boat, and four Ainley’s landed on deck, allowing us to examine their plumage and take some basic measurements (Figs. 1-2).

The only at-sea sighting of Ainley’s was the day we left the island, during lunch (so almost everyone missed it!), but I don’t eat lunch when birding and was able to see three birds flush off the water and snap some images as they flew away from the boat (Figs. 3-5). The views were too brief to get any feel for flight manner, and only an analysis of rump pattern and plumage wear after the event allowed a provisional ID to be made.

Being a winter breeder, adult Ainley’s is not in wing molt in December (unlike adults of the other Leach’s types, which all breed in summer and molt in winter); in addition, adult storm-petrels have subtle clines of wear and contrast in their wing feathers (which are molted over several months), unlike the uniformly fresh juvenile plumage of recently fledged summer breeders. But, without reasonable digital images to evaluate, forget it.

Basically, Ainley’s is a fairly stocky, medium-sized ‘Leach’s’ with a pale to intermediate rump pattern that typically features broad, messy dark streaking. While this rump pattern appears subtly characteristic of Ainley’s (something best appreciated in a series of museum specimens) it is difficult to see and evaluate on a flying bird in the field, and it also seems to be matched by small numbers of ‘northern’ Leach’s.

Thus, molt timing and plumage contrast, in tandem with rump pattern, are the key field ID characters (along with developing brood patches on the in-hand birds!). It’s analogous to identifying different species of ‘Band-rumped Storm-Petrels’ in the Atlantic—and we all know how easy that is.

Also included here are some photos of other Leach’s types we saw, with some comments on ID and molt (Figs. 6-10). The bottom line is we still have lots to learn or, put another way, if you’re not confused then clearly you don’t understand what’s going on. Enjoy!

I thank John Brodie-Good and Chris Collins of Wildwings for putting the trip together, and captain Art Taylor, the crew of Searcher, and fellow participants for helping make the trip a success. More information on the Leach’s complex can be found in Ainley (1980) and Howell (2012), and video of one of the on-board birds can be viewed HERE on YouTube.


Ainley, D. G. 1980. Geographic variation in Leach’s Storm-Petrel. Auk 97:837-853.

Howell, S. N. G. 2012. Petrels, Albatrosses, and Storm-Petrels of North America. Princeton University Press.

Wilson, E. O. 2014. The Meaning of Human Existence. Liveright Publishing Company.

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