Call up the reserves
February 17, 2009
Other commitments kept me from being able to overnight at Moss Island for another week or so, but I managed another day trip on this date. I spent a half day and change in the Rhodes Lake area; Scott was on site as well working around Forked Lake. Whatever Beulah had seen the previous week, it was our only lead so far this year and it had been seen flying from Forked Lake towards Rhodes Lake. It was another grey and quiet winter day. The ornithological high note was a full set of Eagles over Rhodes Lake:
8 Comments:
4:46 is about an hour before sunset on Feb. 24th. This bird may have DKed (I'll assume that's what it was) because of the hunter disturbance, but any thoughts on trying to find roost holes (or a roosting area) by listening for DKs around sunrise/sunset?
My own view on this whole thing is that once you get *The Photo*, then what? How do you study and survey a bird with the rare fly-by? We need to locate roost holes, and IMO the only way to do that is acoustically, with the hope the bird is inclined to DK when entering or exiting a roost hole.
Tanner noted that a mated pair will kent call in the morning. I can't remember the source, but I recall someone else observed or believed that they will sometimes DK in the evenings/morning near the roost holes as well.
I looked at the times of Dan Mennill's recordings in Florida with Geoff Hill. There was a slight bias for DKs within an hour of sunrise and sunset. Some were actually before sunrise (none were after sunset). Maybe that there's a bias isn't meaningful, but a bird that DKs within an hour of sunrise is probably a lot closer to its roost hole that one that does it at noon.
I'll talk about all these things more in upcoming posts. Overall most of our DKs have been heard in the first three hours and the last two hours of daylight. The earliest was 4 minutes before sunrise, the latest was 20 minutes before sunset.
If it is ever determined that these DKs are indeed from Ivorybills, then I think we survey the bird just by listening for DKs. It's the only data that are able to be acquired with reasonable amounts of effort and resources. I don't think we need to know the locations of roost holes themselves if we know the general patterns of spatial and seasonal occurrence and habitat utilization.
My own study of the putative DK's posted on Dr. Mennill's web site indicated a strong peak in early morning and a sharper peak in late afternoon. Both peaks were sharper than the corresponding ones for putative kents, although these also dropped off toward mid-day. I agree that DK's have much potential to provide a proxy for visual observation in estimating population densities. But until clear imagery is obtained, such studies will simply be written off as ghost-hunting.
Eventually an active nest will be found and this will move us forward by leaps and bounds. My guess is that well before this happens, an active roost will be found, and it will yield the first clear ivory-bill images in decades.
This is what I got out of Mennill's data, using the times available from his website and then adjusting for sunrise/sunset on whatever date the recording was made. I tried to only count DK "events", not every DK in a series. I excluded multiples DK if they occurred within a few minutes.
Before sunrise: (3)
Sunrise to +1 hour: (7)
Sunrise+1 to +2 hour: (6)
Midday per hour average: (5.5)
Sunset-2 to -1 hour: (9)
Sunset-1 to sunset: (8)
After sunset: (0)
I'm not sure how meaningful this is (even if we were sure all of Mennill's DKs were actual DKs). We would need to know what causes the ivory-bill to DK in the first place. What's interesting to me, however, is whether they do it near their roost holes, such a call to a mate. That there are recordings very early and very late in the day is encouraging.
I want to follow-up on my own post because I remembered something that wasn't encouraging about Mennill's data when I looked at it before. There doesn't seem to be a meaningful pattern in the DKs, such as evidence a bird using a roost on consecutive days AND consistently DKing while near it. Either:
1. No active roost hole is within ear-shot of the equipment. (very likely).
2. The birds are not revisiting the same roosts (not likely).
3. They don't often DK near their roosts. (?)
4. Other.
You raise some important points, I would offer the following observations for what they're worth.
I have most certainly observed pileateds emerging from their roosts and flying off without drumming or vocalizing. Last year I monitored a cavity tree with a Reconyx camera for about 6 weeks in late summer. The tree recorded a least one pileated roosting within, often two, almost daily. The days in which a least one bird did not emerge from the tree were the exception. Starting in early September, I placed a remote recording device very close to this tree, which obtained recordings daily for the next 3 months. Most days it recorded no pileated drumming. Occasionally it recorded repeated drums, obviously from a bird nearby. More often it picked up only a single drum. But most days no drumming and no vocalizing nearby.
In his study of the Cuban ivory-bill, Lamb observed a female emerging from her roost on several occasions. He stated that she would emerge, fly to a nearby tree, climb it, and within minutes fly 300-400 yards to another tree. There she would vocalize, then "leave the valley."
I would add the following observations of Tanner. Except for nesting birds, ivory-bills in the Singer Tract moved so far so fast that Tanner was unable to keep up with them. This is one reason most of his observations are on one pair of (nesting) birds. A lone ivory-bill observed by Tanner was often absent from one of its known roosts. And importantly, he found no evidence whatever of territorial disputes. These observations lead me to suggest that there is no reason for an ivory-bill, or even a pair of ivory-bills, to confine themselves to a particular roost area when not nesting. When they are in a given area, they may well favor known cavities. But particularly in the pre-nesting period, pairs may be covering large areas of forest in search of quality nest sites.
I'll have a lot of summary discussion here once I finish with the journal though the end of spring 2009. In short, however, *IF* our DKs are from Ivorybills (which remains a big if), the spatial and temporal pattern is completely consistent with what fang describes above. A bird that is highly mobile, usually not even on he site, favoring certain areas but by no means resident in them. We have attempted to track down roosts based on DKs heard shortly before sunset or immediately at sunrise with no success. These eastern fringes of Moss Island would seem to be just one occasional foraging ground within a much larger, and as yet undetermined, home range. More later...
I'll quote this from Tanner, from the second paragraph of Chapter 11:
"The bird usually came out of its roost hole silently, and climbed to the top of of the tree where it would often sit, preen, stretch, and peck with some vigor at the limb on which it was perched. After a minute or so it would call once, then more, single kents; frequently its mate would answer and one bird would fly to and join the other."
This is what got me going down this path. It's reasonable to expect a mated pair to communicate in the morning in order to hook up, since, as Tanner observed, they will roost in different trees, sometimes hundreds of yards apart. But a single bird? Probably not a point to it.
Of course, kents are not as useful to us because they won't carry like a DK will.
Also, in the "Roosting" section of Ch. 11, I interpret Tanner's observations as ivory-bills were very much inclined to repeatedly reuse the same roost holes, though some birds more than others.
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