Monday, November 02, 2009

The Local Big Picture

Overview of Moss Island

All told in 2008 and 2009 we had about 30 different birders spend some time at Moss Island including our crew; 14 birders put in more than two days in the field (not including the local TWRA staff who have routine buisiness on the WMA): The core crew of me, Bob, Scott, and Melinda; Dave Pereksta, Marty Piorkowski and three Cornell volunteers; Alan Mueller and four of the Cornell full-time field staff. Collectively there were nine non-controversial double knock encounters and three controversial ones, along with at least three “brief glimpse” sightings and one or two uncertain “kent” encounters. Total effort hasn't been tabulated precisely, but is probably on the order of 1000-2000 person-hours.

There is an interesting pattern I had not noticed until recently: In each case, the “lower level” encounters (glimpses and kenting) occured within a day of a double knock encounter within the same area. Scott's glimpse and possible vocalization actually occurred in immediate association with his first double knock, Dave's 2008 glimpse was the evening before and about 300m away from the controversial double knock of 3/21/08, Alan Trently's glimpse happened about 7 or 8 hours before and about 500m south of my double knock series on 2/24/09, and my kentings were heard the day before and about 700m away from the spot from which I believe the controversial 3/18/09 double knock series emanated. Yet more circumstantial and insubstantial evidence, of course, but considering that the majority of our field days yielded nothing suspicious these clusters do raise the eyebrows a bit.

Just for fun, let's assume the MIMDKWFTII actually is a real bird, and is not a Pileated. We'll assume that the double knock is its characteristic display, not an abberation. What does the pattern of our detections reveal about this critter? First, it seems clear that though it does repeatedly visit the areas around the lakes in eastern Moss Island, it is not in full time residence there. It seems very unlikely a real diurnal bird could be so hard to find unless it was just not there most of the time. So we appear to have a bird with a large home range, only a portion of which extends into the eastern parts of the WMA -- interestingly mostly within 1000m of the Obion River corridor. It might potentally use the riparian corridors, several of which come together just southeast of our “hot zone,” to move between forest fragments. The bird does seem to sometimes spend the night at Moss Island, but perhaps not in the same place each time. One double knock near sunset, and one series just before sunrise, on different dates (actually, in different years) and in different locations suggest this.

As for behavior, the bird moves a LOT. Going in the afternoon to where it was this morning, or even just a short while before, does not turn it up. It also does not seem to like to cross the lakes. Many hours have been spent on and around Rhodes Lake without the bird ever revealing itself in the open. All the encounters in the immediate vicinity of the lake have been on the east side or to the south beyond the end of the lake; the double knocks have never been heard from the west. Encounters have happened farther west, but never heard from the lake in that direction. Finally while it may be shy of the lake, it is not actually particularly worried about people. The “hot zone” is also the part of the WMA that gets the heaviest use by hunters and fishermen. That squirrel hunter was standing only 100 or 200m from it, with two fairly large dogs, and the bird did not even flee in reaction to the gunshot. No, instead it sat still and double knocked repeatedly from the same spot. Sheesh, I heard the damn thing while sitting IN MY TRUCK parked on a public road. So the difficulties in spotting this bird seem to be a function of: mobility (doesn't stay still very long), large home range (wherever you are, it is usually somewhere else), and aversion to open spaces or even edges. It doesn't actually appear to be shy or skittish, just hyperactive, fast, and stuck like glue to the forest interior.

As an interesting note... most of these features were (are?) evidently typical behavior for an Ivory-billed Woodpecker -- more insubstantial circumstantial evidence. The one exception is the apparent utilization of fragmented forest habitat connected by narrow corridors of several miles in length. As I have written before, if Ivorybills never learned this trick, then there is no way they survived the 20th Century. So regardless of whether this was characteristic of 19th Century Ivorybills, it must be typical for 21st Century Ivorybills or there will not be any of them to look for.

Now for a bit more about the double-knocking behavior of the Mystery Double Knocker. As I mentioned before, its knocking is concentrated in the first three hours and the last two hours of daylight, and from late February until very early April. Given what appears to be the large home range and high mobility, it is hard to actually know if it really only double knocks infrequently, or if it just moves so much between performances that any given observer will not hear it more than once a day. On the one occasion when we had 12-18 people on site for two days, there were three possible encounters, two of them from different locales separated about 500m and 65 minutes. This might argue more for the problem being that the creature is alway on the move rather than its being unnaturally quiet. It does at times appear to react to loud banging sounds by double knocking; as it did this both in response to a gunshot and the double knock simulator it raises the question of whether the apparent "response" to the simulator might in fact just be a non-specific "reaction" to a general loud noise not actually recognized as a "double knock." We might do just as well by simply shooting a .22 at the top of every hour.

Perhaps to contradict myself where I stated that the hypothetical bird is usually not at Moss Island, I can play some numbers games to make guesses as to what fraction of its time it does spend there. First, working in orders of magnitude, we had a "detection" about every 100 hours. Using a general rule of thumb I find useful for many landbirds, 1 detection per hour corresponds roughly to 10 birds per square kilometer. So this detection rate would mean 1 bird per 10 km2, and since we are not hypothesizing more than 1 bird this would suggest a 10 km2 home range for this critter. Our "hot zone" covers about 2 km2, so this gives us a very very rough estimate that the bird would be in the hot zone about 20% of the time. Where is it the other 80%? Who knows? It's still only a hypothetical bird anyway. Just to be intriguing, the hot zone covers about 20% of the forests at Moss Island, so it conceivably *could* be a full-time resident there and the apparent hot zone could still be just a statistical fluke. Or it might spend 80% of its time farther north or south along the Obion - Forked Deer riparian complex, where there are other sizable forest fragments within a few miles.

Something that might argue for a larger percentage of time spent in the hot zone is this simple observation that I had overlooked before: On days when we had 4 or more people in the field, we had a possible detection more than half the time. And again, over the two days when we had 12-18 people in the field, we totaled three possible detections. That pattern might suggest that in fact the hypothetical bird is in the hot zone full-time, or at least visits the hot zone for a while on most days. This scenario would require the bird to be significantly quieter than the average woodland bird to explain the low detection rate per observer.

These are all just games with numbers, patterns, and ideas. We of course do not have any direct evidence as to the identity of our Mystery Double Knocker. None of our sightings are remotely close to "good," and no one anywhere in North America has yet actually identified the source of these double knocks. No quantity of circumstantial patterns, hypothetical scenarios, deduction and inference can ever make an Ivory-billed Woodpecker out of mere noises and glimpses. Whatever our own personal suspicions and hopes might be, we understand perfectly well that we have not "gotten the bird."

Other posts in this series:


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