Possible IBWO Double Knocks from Texas
I have recorded approximately 8 possible double knocks in Texas during
2006, some fit the expected sound better than others.
The following three possible knocks were purposely recorded
hundreds of yards distant from the source sound.
Wave files
Around 7AM
The possible knock occurrs at 2
seconds into the 4 secound recording.
Around 8:30AM The possible knock occurs
around 2
seconds into the 4 second recording. This was low-pass filtered
to screen out
some songbirds.
Around 8:45AM The possible knock occurs
around 1.8
seconds into the 4 second recording.
The parabolic microphone was pointed across a river into about 600
acres of privately-owned tall bottomland woods surrounded by miles
of lesser height almost uninhabitated bottomland woods. The
knocks came from deep within those woods.
Abundant recent IBWO-type scaling was documented from dozens of
trees about 600 yards away from this listening site. We have not
visually checked the location where these three possible knocks came
from for feeding sign.
These recordings were made on a Sony TCM5000 cassette recorder using a
Sennheiser ME62 microphone pointed into a an 18 inch Saul Mineroff
parabola.
Below are spectragraphs of these possible knocks, using Cornell's
"Raven Lite" software. These charts use roughly the same
frequency and time scale as those used for the posted charts at
Cornell's site. Please compare these graphs and soundsto those at
Cornell's site; http://www.birds.cornell.edu/ivory/multimedia/sounds/listening/doubleknock_list/document_view
Possible double Knock at 7 AM
Possible double knock at 8:30AM
Possible double knock from 8:45AM
One day, three of us were standing
in the center of a feeding area with numerous recent scalings and we
heard a non-typical double knock while the recorder was running.
The two knocks are almost twice as close together as they are expected
to be. Possibly this knock is not from a woodpecker. I
believe this is the knock given by an IBWO that has discovered us in
the middle of his feeding area. We have heard this rapid double
knock before on entering the feeding area without much attempt on our
part to be undetected.
Non typical possible "double knock" sound
Spectragraph of the non typical sound below
Possible alarm double knock