Identifying all of the world's gull species, travel aside, sounds like an impossible task.
OK, not impossible. But nothing to bet your life on. Too many species are, at first glance, look-alikes.
Finnish birder/photographer Klaus Malling Olsen will help you do that, however, with his new guide book, "Gulls of the World, a photographic guide."
There are only a few more than 50 gull species, total. Smallish number notwithstanding, they pose, according to the publisher, "some of the greatest field identification challenges of any bird group."
No kidding.
The problems are age-related plumage changes, variation within species, hybrids, and complex distribution.
ID disagreement is not uncommon, even among gull fanciers, like those who shiver on Lake Harriet's shore in late-fall twilight. Prior to ice, they are watching gulls return from garbage-dump scavenging, coming for nighttime roost.
In recent Novembers birders have been watching for Lesser Black-backed Gull, an unusual but recently regular visitor with deceiving plumage. (It frequently is seen, so observers say, but very hard to pin-point with a pointed finger.)