Henslow's sparrow night flight call
August 10, 2005 - topic contributed by Bill Evans
Nearly ten years ago (October 31, 1995) I recorded an unusual night flight call in northeastern Oklahoma (Fig.1). I first surmised that the call was from a Henslow's Sparrow in 1997 when I noticed a correspondence with spectrograms of diurnal Henslow's "tseep" notes I had recorded in New York State (see Fig. 2). The calls were characterized by a descending, frequency-modulated, tone up to 200 ms in duration. The modulations had about a 2 kHz frequency bandwidth in the 7-10 kHz range and were roughly 55-65 ms per cycle. In some calls the bandwidth of the modulations increased as the call progressed. The unique feature that stood out and connected the Henslow's diurnal calls with the Oklahoma nocturnal flight call was a double-peaked crest at the top of the high frequency portion of the modulations. Though this characteristic was less pronounced in the night flight call, it was clearly present and was such a unique feature -- I had never seen anything like it in the somewhat similar flight calls of White-throated Sparrow or in any other species.
Fig.1. Possible Henslow's night flight calls recorded near Bartlesville, Oklahoma on October 31, 1995.
Fig.1. Henslow's Sparrow diurnal contact call ("tseep" note) recorded from a visually-identified, perched bird July 25, 1995 near Ithaca, New York State.
In 100's of thousands of night flight spectrograms I had inspected from eastern North America, I'd never seen anything like the calls in Figs.1 or 2 until I recorded the night flight call in Fig. 3 near Alfred, NY on October 11, 2004. While different in some respects from the calls in Figs.1&2, the call has the unique double peaked feature and the peaks were 63 ms apart -- in the range of the peak separation in my diurnal Henslow's calls. In addition, the length and frequency characteristics of the call matched. I went back and looked at variations of the diurnal Henslow's I had recorded in New York State in 1995 and found the call shown in Fig. 4, which appears to be a closer match to Fig.3 than Fig.2. I look forward to any comments on this matter of Henslow's Sparrow night flight call.
Fig.3. Presumed Henslow's Sparrow night flight call recorded October 11, 2004 near Alfred, NY.
Fig.4. Henslow's Sparrow diurnal contact call ("tseep" note) recorded from a visually-identified, perched bird July 25, 1995 near Ithaca, New York State.
Re: Henslow's Sparrow night flight call ( Mark Armstrong)