Sunday, March 31, 2013

Tennessee Bird Records Committee accepts Hooded Crane

As committee chair Kevin Calhoon recently announced, the Tennessee Bird Records Committee has voted to accept the 2011-2012 occurrence of a Hooded Crane at Hiwassee National Wildlife Refuge in Meigs County, Tennessee, as a wild bird. The vote came after over a year of research and discussion. Though the vote was split 5-1, the spirit of "reasonable people with the same information can reasonably reach different conclusions" prevailed and the discussion was respectful and without rancor. This was the third report of this species in North America; it is widely felt that all three records likely pertain to the same individual bird. What is almost surely the same bird also appeared in Indiana a few days after it was last seen in Tennessee, making a total of four occurrences in four states. The bird's stay in Tennessee was the longest of the four, and it was seen by far more people here than at any of its other stopovers. Hence it seems fitting that we are the first state to formally act on the species, making this the first BRC-accepted record of a Hooded Crane in the New World. ***EDIT*** I've just learned that Indiana accepted their record also, so we were not the first! Ah well. Not sure why the Indiana vote seems not to have been widely known.

I was in the majority on this vote (which has not always been the case on other recent split decisions!). The species identification was never in doubt, so the only question was whether the bird was of wild or captive origin. As is often the case, there was no direct evidence one way or the other, so we had to make our best judgement from circumstantial evidence instead. This raised the issues of standards of evidence and review philosophy, about which many different opinions were expressed in discussions on blogs and listservs. Some people advocated a "presumed wild until proven escapee" approach, while others advocated the opposite. Either way, this also raises the question of what the standard for "proof" is: Beyond a reasonable doubt? Beyond a shadow of a doubt? The preponderance of the evidence? If you will forgive a bit of legalistic philosophising, I'll describe how I approach this.

In general, and in this case specifically, I invoke the old standby of "When in doubt, leave it out." This applies equally to doubt about species ID and doubt about wildness. Many people seem to accept this criterion more readily for ID than for origin; but to me they are exactly equivalent. As for what constitutes "in doubt," I believe that the standard should be the time-honored "reasonable doubt." Expecting proof beyond all doubt is an impossible standard, as there is almost always some scenario that can be imagined and invoked to explain anything. So what is a "reasonable doubt?" I find this definition from the Supreme Court of Canada to be the most instructive:

"A reasonable doubt is not a doubt based upon sympathy or prejudice, and instead, is based on reason and common sense. Reasonable doubt is logically connected to the evidence or absence of evidence. Proof beyond a reasonable doubt does not involve proof to an absolute certainty. It is not proof beyond any doubt, nor is it an imaginary or frivolous doubt."

I also think that the questions should be, "Is this bird correctly identified?" and, "Is this bird wild?" The questions should not be, "Is this bird misidentified?" or, "Is this bird of captive origin?" The difference might seem trivial, but if you think about it in depth you will see it is not. Suppose you have someone claiming a California Gull based on its having been bigger than a Ring-billed Gull and darker on is back, with no other details. If your question were "Is this bird correctly identified?" you clearly would have reasonable doubt and would conclude the record should not be accepted, since many other species of gulls could fit that description. On the other hand, if your question were "Is this bird misidentified?" then you would also have reasonable doubt (it could be a California Gull based on the description), so you would not be able to reject the record. Obviously the former conclusion is the appropriate one for a BRC member to reach.

Getting back to the Hooded Crane, the question is "Is this a wild bird?" My initial reaction on first hearing of the record was that it probably was not; this seemed like "common sense." However, without investigating the report further, this is in fact a doubt that is based on "prejudice" (see above) not on "common sense" and "evidence." And as I did examine the actual evidence (circumstantial though it may be), I found my "reasonable doubt"about the birds wildness growing smaller and smaller.

To go through it in detail, I felt the "wildness" question could be broken down into several more specific points. First, what is the nature of the captive population from which an escapee could have originated? This was much discussed. Kevin Calhoon is a member of the zoo and aquarium professional community, so he took the lead on researching this. What he found was that the captive population is very small and tightly controlled. The small number of birds that went to private collections are generally pinioned. There had been concern about the birds in Idaho that "disappeared" from a private collection several years ago. It appears that these birds were not actually known to have escaped, and they are known to have been pinioned (which is permanent) so could not have been the source of the intact, free-flying bird in Tennessee. There were no other indications of any other missing birds or potential sources for unaccounted free-flying escapes. No strong basis for reasonable doubt shows up here.

Second, does the wild population have a history of long-distance vagrancy sufficient to get a bird across the Bering Strait and into North America? The answer to this is a definite "yes." There are vagrant records over 1000 miles outside of the usual breeding and wintering ranges in Asia, and by one account as far as in European Russia. The distance from the breeding grounds to the Alaskan mainland is not much greater than this, and the Siberian region the bird would have crossed is almost entirely devoid of birders. It is also worth remembering that Sandhill Cranes have strayed to Great Britain and continental Europe, a distance and direction similar to that required to get a Hooded Crane to North America. Even if this vagrant scenario seems unlikely, the wild population is about 100 times larger than the captive population, and is free-flying and unrestrained. So adjust the improbability factors in accord with this, and see how they feel. Again, I find no basis for reasonable doubt here either.

But, this scenario only gets the bird to Alaska in the company of Lesser Sandhill Cranes. Is it feasible for the bird to then get thousands of miles farther east, most of the way across the continent, and in the company of Greater Sandhills? I would think it certainly is. We have something of an analogue in the Common Crane, a more frequent vagrant to North America. Common Cranes believed to be wild birds from Siberia have made it east to Indiana and Quebec, putting them in the same Greater Sandhill population that winters in Tennessee. If the Nebraska bird was the same individual as the Tennessee Bird, then it would have had the entire summer to wander in the far north, unmated and not tied to any nesting territory. It very easily could have continued its eastern drift and wound up with the eastern Sandhills, then migrated south with them. So, if a bird can get to Alaska in summer, then it is not at all unreasonable that it could wind up in Tennessee in winter, especially if it has been in North America for a year or two already.

The final two-part question is, do the circumstances and behavior of the bird agree with what would be expected from a wild bird, and are they at odds with what might be expected from a captive? Again, I believe the answer is yes and yes. The bird in Tennessee was with migratory Sandhill Cranes, and when spring came it migrated north with them, being seen briefly in Indiana. The same was true in Nebraska the previous spring, when possibly the same bird was see with migrating Sandhills. This is precisely how we would expect a wild Hooded Crane to behave. But do we know that an escaped captive would not do the exact same thing?

We don't know for sure, but there is another Common Crane analogue that I found informative. This is the case of "Ol' Crooked Toe," a captive Common Crane that escaped from captivity in New York in 1993. So far as I know, this is the best-documented situation in which a known captive exotic crane escaped and "went native," being seen repeatedly in the wild in the company of wild Sandhills. His tale is recounted here:

This bird had a distinctive but non-crippling injury to one toe, allowing it to be identified definitively. In all its years in the wild, it traveled all the way from New York to New Jersey, where it settled down, attracted some wild Sandhills to join in, and raised a flock of non-migratory hybrid offspring that probably remain in the same area to this day. The things I find most relevant about Ol' Crooked Toe is that it did not wander vast distances across the continent, it did not take up with migratory Sandhills, it did not turn up in the staging grounds for the wild cranes. It stayed close to home, found a suitable spot, and settled down. The wild Sandhills joined it, not vice versa.

Given all of this, I felt that the question of wildness was settled for me "beyond a reasonable doubt." Every aspect of the circumstances of this bird was exactly what would be expected if the bird were wild, and there was no contrary evidence, direct or circumstantial, and no apparent likely source for an escapee. I found this an interesting comparison to another recent split decision for our BRC where I was in the 4-2 minority voting to reject a bird because of doubts of wild origin, in spite of strong and vigorous arguments from other committee members who felt otherwise. Tennessee only allows one dissenting vote, so the two negative votes in that case overrode the majority and rejected the record. That time the circumstances left me with what I judged to be reasonable doubts; it was not definitive, but I was uncomfortable setting my doubts aside and I felt I must vote to "leave it out." In the case of the Hooded Crane my initial strong knee-jerk doubts were assuaged by the actual evidence.

I am only speaking for myself here, of course. Other members of the committee are free to discuss their votes or not; I will say that the rationales of the others who voted to accept were in general not radically different from my own. We also knew going in to this that no matter how we decided, there would be hundreds or thousands of people who would think we were wrong!


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