Wednesday, February 18, 2009

Something new in the Ivorybill world?

This has come up recently over at In response to discussions about things that go bump in the woods, "Fangsheath" posted a link to the Singer Tract recordings of real, for sure Ivorybills communicating with each other. Mixed in with the vocalizations are rapping sounds, which alas do not include any double raps** of the sort typical of other Campephilus species and described for the Ivorybill in many historical accounts. But what the posters in that forum have discussed is that the ordinary-sounding raps actually might be occurring in a consistent, repeated pattern, rather like a very slow-motion drum. Take a listen for yourself (the audio clip runs about 10 minutes; it consists of the same 5-minute sequence played twice):

This may seem silly and unnecessary, but I remind everyone ONCE AGAIN that these are for sure, real, unquestionable Ivorybill sounds recorded in the 1930s by people who were watching the birds make the sounds; I'm not just going off the deep end babbling about odd noises of unknown origin in some random tract of woods.

The thought here is that what initially sound like innocuous series of raps actually seem to follow a consistent, repeated pattern, a short sequence that in at least one occurrence accelerates: Rap...Rap...Rap...Rap..Rap..Rap. Remember that these birds are at an active nest, so these raps are communication, not foraging.

Examining it in detail reveals the following:

A total of 9 rap series, ranging from 3 to 11 raps. The median rap spacing ranges between series from 0.13 to 0.29 s, but within an individual series the range is much smaller, about 10-20% between the longest interval and the shortest one. In every case but one the series accelerates from the first to the last interval (by about 10-20% of course). In the one exception, the series accelerates for the first 4 intervals, then decelerates for the final 2. These numbers are just from my first pass through, I will not be surprised if a more detailed analysis changed them in detail but not in overall patterns. This to me is actually pretty suggestive of a patterned display, not just casual rapping. I leave to others the semantic distinction as to whether this constitutes a "drum" or some other term.

Very interesting possibility that this might be a specific, stereotyped pattern and not just banging on trees. If so, and if any of us have actually been hearing Ivorybills banging in the woods in recent years, one might expect that this display should be heard as well, perhaps more often than the double rap.

Anyone wanna reanalyze a few gazillion hours of ARU data?

**It is always said that this recording includes no double raps; however, what ARE the more muffled sounds at 121.5 and 124.1 sec, then? These are part of what sounds like a more distant rap sequence responding to the closer rap series. They sound to me like double raps with a fairly long interval, about 0.18 sec between the raps, more like the Florida ARU sounds than the Arkansas ARU sounds and not like what was historically described as a very short interval between the raps. Of course this spacing is in the range heard in the longer series, so perhaps these might better be considered "series" of just 2 raps, which might be distinct from the true and undocumented "double rap." Interesting... even with such limited hard data, there still might be more things to be discovered in it!


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