Ah, the Common Cuckoo. Undoubtedly California's best bird of 2012, and undoubtedly a bird that flew a long ways from home. Photographed in Watsonville, CA.
Birders, it's time to put the kibosh down. Over the years, I've heard birders questioning the origins of high (and low) quality vagrants more and more often. Some skepticism is certainly healthy, but needlessly claiming a rare bird is someone's escaped pet is bad for everyone. This is a disturbing trend, to say the least...it is a persistent pattern observed in birders, and is often based on a lack of understanding of natural patterns of occurrence, how birds migrate, and what birds are and are not frequently kept in captivity.
In case you are not up on this contentious and very nerdy issue, let me catch you up. Birders like seeing wild birds. However, not all birds that live in the wild got there on their own. If you go to the duck pond at your local city park, you will probably come across Muscovy Ducks. They may be able to live there without supervision, but the chances that this popular barnyard bird migrated from a wild population in Central America is about nil...something we can all agree on. They are no more wild than the peacocks that get the run of your local zoo.
Problems arise when birders poo-poo a naturally-occurring bird as an escapee when there is little to no evidence to back it up. This happens over and over again, and I think less experienced birders may be prone to heeding these uninformed opinions.
For example, a friend and well-known California birder who goes by Red Phalarope Man instantly shat upon the Black-bellied Whistling-Duck (to his credit, not literally) that showed up for a brief period in the middle of the state last May. He was completely convinced it was a bird that had escaped captivity. Although there was the very small possibility he was correct, there was no compelling evidence suggesting it was anything but a wild bird, which had occurred here a few times in the past. Sure enough, you may remember last summer was a huge year for Black-bellied Whistling-Ducks that wandered far north of their usual range all over the country. Our bird, since accepted by our state's Bird Police, was just leading the first wave. Any unwitting birder who may have paid Red Phalarope Man too much heed may have passed on chasing this California MEGA, something they would have regretted for the rest of their life.

Emperor Goose is a species that has been questioned as naturally occurring outside Alaska, but has a proven regular track record of occurrence at coastal sites in the western U.S. during the winter (which is when and where one would anticipate them). If Emperors were really being released willy-nilly, you would expect them to be found all over the country, at all times of year. This vagrant Emperor Goose was photographed at Ocean Shores, WA.
Escaped birds usually come in 3 flavors:
1) Waterfowl collections and zoos. You or I don't know anyone who collect exotic ducks and geese, but these bird hoarders are out there. They hold really bizarre and exotic birds that could also migrate here from their native lands...sometimes. While I have seen some species in the wild that unquestionably originated from these bird collections (i.e. Ringed Teal, Black Swan, Egyptian Goose), people are always questioning the legitimacy of vagrant waterfowl...White-cheeked Pintail, Falcated Duck, Smew, Barnacle Goose, Bean Goose, you name it, these birds always raise doubts among certain people when they are found on our shores.
This undoubtedly wild Harris's Hawk is part of a family group that is resident in Jacumba, CA.
2) Falconry birds. Falconers keep a variety of hawks and falcons of both species that are native and not native to the continent. Sometimes they escape. I have seen a Harris's Hawk perched, with jesses, on the TV antenna of Dipper Dan's house in the Sierran foothills of Angel's Camp, CA...certainly not a wild bird, and not in a very likely place a wayward vagrant would appear.
In California, our state Bird Police for many years bizarrely refused to accept Crested Caracara as a naturally-ocrurring vagrant, despite their regular and repeated visits all over the state. They have since become less ultraconservative (always a good thing, amirite?) and accept new records of this bird just about annually.
Black-throated Magpie-Jays roam free in the Tijuana River Valley, just south of San Diego. This is a great example of an obvious escapee...it's a nonmigratory species that is found nowhere near San Diego, but is known to be kept in captivity (unfortunately) just across the border in Mexico.
3) Cage birds. This category includes parrots and many Carribean and Mexican birds that were likely caught in the wild but were released or escaped far from where they were kidnapped. Many species that fall into this category are known. However, birders often get too wrapped up in the "cage bird" hypothesis, i.e. the Red-legged Honeycreeper found during spring migration on the Dry Tortugas that was rejected by the state's ostensibly then-corrupt Bird Police.
Most experienced birders have encountered at least a couple of birds that truly fall into one these "escaped" categories in the wild. California seems to get a lot of them...mixed with wild birds in wild settings, I've run into flamingos, Pin-tailed Whydah, Red-billed Leothrix, Black-backed Oriole, White-collared Seedeater, Phyrruloxia, Blue Mockingbird, Gray Silky-Flycatcher, who knows how many kinds of parrots and parakeets...the list goes on.
Brambling is one of many Siberian/Asian birds that make a wrong turn during migration and show up in North America. This one spent a winter in Woodburn, Oregon.
So how does one avoid being overly cautious? Learn about the species in question. Does it have an established pattern of occurrence? Is it a long distance migrant? Where have strays shown up in the past? Would it be more likely to find in certain seasons than others? There is much wisdom to soak up from other birders, but not the self-proclaimed authorities who rank a lot lower on the Global Birder Ranking Scale than they think they do...and it can take more than some decent bird ID chops to really sort these folks out.
There are known repeat offender escapees, and known areas where there are high concentrations of these birds as well. For example, southern California gets all kinds of bizarre stuff, mostly on the coastal plain; it is widely believed that these birds originate from cage birds just over the Mexican border. Florida is awash in strange exotics as well.

A recent instance where the Cage Bird Conspiracy came up was when a Common Cuckoo (a long-distance Siberian migrant) spent some time in California this fall. This species occurs rarely but regularly on Alaskan islands during migration, so as with other "sibes", birders have always known that a stray could potentially fly down the west coast of North America. There is a definite pattern of this happening with many other species...many Asian-flavored waterfowl birds, plovers and sandpipers, Red-throated Pipit, Northern Wheatear, wagtails, etc. stray regularly to Alaska, and sometimes down into Canada and the Lower 48. When you look at the above map, you can see that the Bering Strait separates Alaska's Seward Peninsula and easternmost Russia by a mere 50 miles or so...it is no stretch of the imagination to think a lost Russian bird could find themselves migrating down the wrong coast by mistake. However, to invent a scenario in which a Common Cuckoo is born in Russia/East Asia, captured, sold to a tourist, taken to the United States and somehow freed during the height of fall migration (something a couple birders insinuated) sounds more like Hollywood to me. And yes, that is a movie I would see.
What about ship-assisted birds you ask? Well, that is another blog post for another time.
Pin-tailed Whydahs are becoming increasingly common in southern California, and have now been reported at least twice as Fork-tailed Flycatchers. This is also an annoying trend, but misidentifications always have and always will happen. Whydahs are African birds, so based on the fact that no passerines migrate between North America and Africa (except Northern Wheatear?!), we can deduce that this is not a true vagrant.
Of course there are instances where escaped birds are mistakenly considered naturally-occurring as well, but I feel those cases are a bit easier to sort out. It is certainly true that birders are falliable and are probably not correct 100% of the time in either case...as the Human Birdwatcher Project reminds us, "birders are people too!".