With regards to the topic of origins i think it's worth considering the standard by which we confirm the natural vagrancy of a bird. Is the goal to prove that a bird is absolutely wild or is it to determine if the bird is likely wild beyond a REASONABLE doubt?
Its nearly impossible to prove a bird's origin with absolute certainty without banding records. For this reason I'd suggest the role of any records committee is to determine if the bird can be presumed wild beyond a reasonable doubt. Consider this before we deal with the example of the chaffinch-- Do we hold a double standard for rarities? When we see a House Sparrow do we scrutinize to determine if its an American-born bird or a vagrant? No. And why not? Because it's overwhelming likely that any given House Sparrow we see is domestically born even though its possible that it could be a vagrant (besides, there's probably no way to differentiate between the two anyway). Do we stress over the origin of every Rose-breasted Grosbeak we see? The answer is no, though I have seen them for sale in Central America and inevitably some of the birds escape and enter (or re-enter) the population. Why is it ok to be very careful with one species and careless with another?
This brings me to the chaffinch. We treat a bird like this differently because its unusual. We scrutinize it in a way we never would scrutinize the origin of a Mute Swan or European Starling--both birds in North America that could potentially originate from either foreign or captive populations. What can we tell about the bird? It shows no unusual wear. It has no bands. It seems to socialize normally (though some of us from across the pond would be better able to assess that than I). It's a member of a very common species in it's home range. There is at least a scant precedent of European finches being seen in the northeast, some of which have been accepted by various record committees.
I'd like to address the issue of escapes. How many people have walked into a pet store and seen a chaffinch or greenfinch for sale. I would be willing to put money down that almost none have. Why? because they are not kept as pets. The ARE kept by serious aviculturalist. These hobbyist are to motorists as someone who rebuilds a classic car is to the average driver. They are in another class altogether. Over the years I have kept 40 or so 'finches' of various varieties. I have combed though the internet for resources on such birds. I've visited dozens of pet stores to buy and sell birds. I have even looked into mailing lists and membership websites. In all of this I have seen NO chaffinch or greenfinch for sale in the United States. I have seen some solicitations looking for these species, but that's it. What does this tell me? There are a few out there, but they are exceedingly rare among cage birds and they are kept by only the most serious collectors. This type of serious aviculturalist BANDS THEIR BIRDS! We are not talking about a twelve-year-olds with a first parakeet who may take Polly outside only to have it fly away or escape through a window. These are adults keeping expensive and therefore well-guarded birds. Lumping the two would be like treating exhibits from the Smithsonian with the same care as 6th grade school projects. Fringillid finches tend to be 'ugly' compared to Cordons and Gouldians, difficult to breed compared to Zebras and Lonchura finches, and 'dumb' compared to parrots and lovebirds. 'Pet' owners don't usually want them, hence you don't see them in pet stores.
Next, many states--NJ for example--require breeders of all but a few species to obtain permits for reasons of environmental protection. No chaffinch or greenfinch can be bred legally in NJ without a permit. The same is true for Eurpean Goldfinch, a bird I have seen a few times in pet stores (and with plumage in poor condition because fringillid finches are not well domesticated as grassfinches are). Such goldfinches invariably are BANDED because of their origin with registered breeders.
What's my point? A Common Chaffinch shows up at a feeder in NJ. Most chaffinch in the world are wild. Its plumage and behavior DO NOT suggest a captive bird specifically, so why assume? Chaffinch are kept by aviculturalists, but the number of such birds is quite small among 'pets' and the number of unbanded individuals would be only a tiny fraction of that tiny fraction. Our bird is not banded. Is it more logical to assume its a tiny minority of a tiny minority or a minority vagrant member of a huge population of birds? I'd argue that a tiny chance (vagrant) is still more likely than a very small chance x an unlikely chance x a tiny chance (escaped, unbanded, scarcely kept species). Fact is, we can never KNOW the bird's origin with absolute certainty. If our European observers confirm this bird behaves like a typical, wild chaffinch and it lacks bands or obvious aberrations to appearance that might suggest being captive, can't we conclude beyond a reasonable doubt that the bird is most likely wild? I'd say yes.
Good take on this, thanks.
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