Double Knocks From Arkansas

We have discovered a variety of sources that produce double-knocks and "kent"-like calls during field searches and on recordings made by autonomous recording units (ARUs). There are still some sounds that are not easily explained by an alternate source. If the sound matches what we expect an ivory-bill to produce, and our expert reviewers cannot definitively attribute the sound to one of the "sound-alikes" we encounter, the sound is categorized. We may categorize the clip as "plausible" and assign a score, as explained in the section about rating sounds.

To play the recordings, click on the arrow in the lower-left corner of the each frame. The horizontal axis measures the length of the clip in seconds.

Recorded March 28, 2006



ANALYSIS
Context: Very active morning with at least three different woodpeckers drumming. The drum bursts at the beginning, at three seconds, and at 21 seconds, are similar in energy distribution, indicating it is one bird. Drumming at five seconds, nine seconds, and 15 seconds are also similar to one another, indicating it is the same bird. Finally, double-knocks occur at approximately 11 seconds and again at 15 seconds. The energy distribution is similar in both but markedly different from the other recorded drumming, indicating it is a third bird. Both double-knocks received the same category and score. The inter-strike interval for the first double knock is 64 milliseconds, and 60 milliseconds for the second double knock presented.
Category: P1
Score: 3

Recorded January 27, 2006 

ANALYSIS
Context: Double-knock at approximately 10 seconds into the clip. A heron squawks at approximately 19 seconds. The inter-strike interval is 105 milliseconds.
Category: P1
Score: 3

Recorded March 07, 2006


ANALYSIS
Context:
A very active morning, bursts of drumming from other woodpeckers  occur at two seconds and eight seconds into the clip. Just after the second burst of drumming, at approximately nine seconds, a crisp double-knock occurs. The double-knock registers at a lower frequency than the drumming bursts, indicating it is a different bird. The inter-strike interval is on the slow side at 119 milliseconds, but within the possible range.
Category:
P1
Score:
3

Recorded January 24, 2006


ANALYSIS
Context:
An isolated and faint double-knock approximately 11 seconds into the clip. Ivory-bill cannot be objectively ruled out. The inter-strike interval is on the slow side at 105 milliseconds, but within possible range.
Category:
P1
Score:
3

Recorded March 15, 2006




ANALYSIS
Context:
A very active morning with at least four woodpecker species drumming. The double-knock occurs at 19 seconds into the clip, the energy distribution is sufficiently different from all other drumming activity to indicate it is a different bird. The interval between the two knocks is 82 milliseconds.
Category:
P3
Score:
2

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