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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Sound, Bulgaria (1 Viewer)

Insects where I live (in central Poland) seem to chirp at around 10kHz, but I haven't researched that well, and there may indeed be other species here, and especially so further south, in Bulgaria.

Re the recording: Considering whether the sound in question was heard during the day (when insects seem to be less active) or later in the evening might help to narrow down the choices. Also, compare the length and shape of the vertical lines in your sonogram with sonograms of known Grasshopper Warbler songs because they differ in at least some cases. Whether there were there only one or two individuals making such sounds or the whole meadow around you could sway you in the right direction as well. Plus, if I were you, I'd seek confirmation from both BirdNET and Merlin, particularly if you couldn't ID it as a Grasshopper Warbler with certainty in the field.
 
Thank you for all comments!
The sound was recorded on 11.05.2023 at 07:00 AM in area with scattered Paliurus spina-christi bushes and about 7°C of the air.
Attached capture from video of the habitat.
Maybe is Locustella fluviatilis, based on most comments and sonogram in xeno-canto:

ID Unknown from Bulgaria (XC800772) :: topic 55798 :: xeno-canto

xeno-canto.org xeno-canto.org
Still, I have doubt of the species, because of several reasons (individual differences, weather, distance, etc.), which may lead to changes in the normal range of sound hearing or recording of particular source. And in such cases, for safely ID, maybe is better visual contact with the source to be made.
sound_ID_habitat.jpg
 
I'd be inclined to trust the two people who identified the bird for you on XC because of how experienced they are with bird sounds. While I don't consider myself fit to confirm the ID myself by ear, I suspect other people who do may be biased to first consider Grasshopper Warbler (instead of River Warbler) not because it's so hard to separate this species pair, but because Grasshopper Warbler would be the default cricketlike warbler in much of Europe (except for Savi's Warbler in some areas, which has a much faster pulse rate and much lower frequency). Have a look at River Warbler's range to see why.

Also, if I were you, I'd switch to recording in the lossless .wav format instead of .mp3. Here's my recording of a River Warbler identified as such by BirdNET (the benefits of .wav's), from last year. As you can see, the thickest part of the reeling falls between 4 kHz and 8 kHz, just as in your recording, which excludes Savi's Warbler. Let's have a look at the pulse rate: the Sound Approach has it at 10 per second, in my recording it's about 16.4 per second, and in your recording it's sbout 15.25 per second. Common Grasshopper Warbler has 24 per second in the Sound Approach, and analysing a few sonograms of XC recordings seems to confirm just that. https://www.researchgate.net/public...bler_Locustella_fluviatilis_in_eastern_Poland, which has a great visualisation of RW and GHW songs side by side, has it at 9.5-16.5 per second for River Warbler and 22.5-25 per second for Grasshopper Warbler.

There's also Lanceolated Warbler, which is only present in Finland and further east; a quick and dirty look at the sonograms of this one appears to show it having a slightly different core frequency range to River Warbler, but this impression may be inaccurate, and Lanceolated Warbler is out of range by a long shot anyway. I hope someone with more direct knowledge of Lanceolated Warbler could chip in.

One more thing, I wouldn't hope for visual contact with any of the above unless you have much luck or are prepared to chase the bird and trample its habitat/scare other animals/get a bunch of ticks (in the non-birding sense).
 

Attachments

  • River Warbler.wav
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  • Screenshot_20230515-111932_Chrome.jpg
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01101001 said:
I'd be inclined to trust the two people who identified the bird for you on XC because of how experienced they are with bird sounds. While I don't consider myself fit to confirm the ID myself by ear, I suspect other people who do may be biased to first consider Grasshopper Warbler (instead of River Warbler) not because it's so hard to separate this species pair, but because Grasshopper Warbler would be the default cricketlike warbler in much of Europe (except for Savi's Warbler in some areas, which has a much faster pulse rate and much lower frequency). Have a look at River Warbler's range to see why.

Also, if I were you, I'd switch to recording in the lossless .wav format instead of .mp3. Here's my recording of a River Warbler identified as such by BirdNET (the benefits of .wav's), from last year. As you can see, the thickest part of the reeling falls between 4 kHz and 8 kHz, just as in your recording, which excludes Savi's Warbler. Let's have a look at the pulse rate: the Sound Approach has it at 10 per second, in my recording it's about 16.4 per second, and in your recording it's sbout 15.25 per second. Common Grasshopper Warbler has 24 per second in the Sound Approach, and analysing a few sonograms of XC recordings seems to confirm just that. https://www.researchgate.net/public...bler_Locustella_fluviatilis_in_eastern_Poland, which has a great visualisation of RW and GHW songs side by side, has it at 9.5-16.5 per second for River Warbler and 22.5-25 per second for Grasshopper Warbler.

There's also Lanceolated Warbler, which is only present in Finland and further east; a quick and dirty look at the sonograms of this one appears to show it having a slightly different core frequency range to River Warbler, but this impression may be inaccurate, and Lanceolated Warbler is out of range by a long shot anyway. I hope someone with more direct knowledge of Lanceolated Warbler could chip in.

One more thing, I wouldn't hope for visual contact with any of the above unless you have much luck or are prepared to chase the bird and trample its habitat/scare other animals/get a bunch of ticks (in the non-birding sense).
Click to expand...
Thank you for your detailed explanation!
Based on BirdNet, on my recording is also Locustella fluviatilis.
 
Although BirdNET makes mistakes (even more often than Merlin, which also does), it is, nevertheless, useful in steering one towards an ID or confirming already well-founded suspicions (still, visual and aural comparison with sonograms and the sound of other recordings is often required to clinch the ID of less common birds, which is what I try to do not to skew the database).

Re Lanceolated Warbler, internet sources say its song first rises and, then, falls. River Warbler's song appears to be steady in that respect.
 
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Yes, it´s a River Warbler. Always try to make as long recordings of bird sounds as possible, that makes the identification much more probable. A minimum of 30 seconds is a good goal - yet not always possible ;)
 

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