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BitBatty
Feb 9, 2018, 7:38:40 PM2/9/18
to Australasian bat call group
Hi all
I have some calls from Somersby, (north of Sydney) NSW - Sandstone country not near water. It is from stag watching a hollow tree on dusk, but I don't know if these bats actually came out of the tree. The calls are in zero crossings format - recorded using an Anabat Express. I don't have any full spectrum recordings.
I tend to use the Bat Calls of NSW guide to separate Myotis and Nyctophilus using the following distinguishing features:
- Nyctophilus pulse interval >95ms and initial slope < 300 OPS. Often with 2 changes of frequency in the lower half. Calls usually fragmentary due to quiet calling.
- Myotis with a central kink at 47-50kHz, often with a gap when flying over water, pulse interval <75ms and initial slope > 400 OPS. Pulse angles tend to change from pulse to pulse, making a messy looking call sequence.
I have really enjoyed the Myotis discussions here in the past. So I thought I would throw what i think are Nyctophilus sequences in to see what other people think and to learn some more.
The calls are really good quality and I think that they are Nyctophilus (lower kinks, not messy pulses, site not close to good Myotis habitat). But there are lots of pulse intervals of <75ms and initial slopes of 400 OPS that are meant to be more features of Myotis. Is this just due to the higher quality of the calls than we typically get from Nyctophilus (ie the detector is not missing lots of the pulses).
Or are the calls not from Nyctophilus / Myotis at all? Are they an excited call from Scoteanax rueppellii / Scotorepens orion / Falsistrellus tasmaniensis? I think that this is unlikely as the pulses are not extremely close together like you get with an excited call.
Anyway food for thought!
AM
Leroy Gonsalves
Feb 9, 2018, 9:30:24 PM2/9/18
to kilo...@googlegroups.com
Hi Anna,
Interesting calls. Was there a lot of clutter?
I thought quite a few pulses looked like they could be 'steepish' S. orion calls. I guess that could be the case if bats were leaving the stag.
Cheers,
Leroy.
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BitBatty
Feb 9, 2018, 10:13:00 PM2/9/18
to Australasian bat call group
Hi Leroy
Haha you know that was my first instinct (Ft/So) when I saw them, but then I thought that they were a bit too steep and checked a few Nycto ref calls and there are a few on there that look a bit like these. That set me on the Nycto path. Do you think that the sequences are a bit too long and a bit too curved for Nyctos?
I didn't record them, but apparently the habitat was the heathy shrub woodland that is common in Somersby. So a pretty open canopy above a dense Banksia shrub layer. The Anabat was placed on top of a ute on a track aimed straight up. There were 2-3 hollow trees within 10-15m.
AM
On Saturday, February 10, 2018 at 1:30:24 PM UTC+11, Leroy Gonsalves wrote:
Hi Anna,Interesting calls. Was there a lot of clutter?I thought quite a few pulses looked like they could be 'steepish' S. orion calls. I guess that could be the case if bats were leaving the stag.Cheers,Leroy.
On 10 February 2018 at 11:38, BitBatty <annam...@hotmail.com> wrote:
Hi allI have some calls from Somersby, (north of Sydney) NSW - Sandstone country not near water. It is from stag watching a hollow tree on dusk, but I don't know if these bats actually came out of the tree. The calls are in zero crossings format - recorded using an Anabat Express. I don't have any full spectrum recordings.I tend to use the Bat Calls of NSW guide to separate Myotis and Nyctophilus using the following distinguishing features:
- Nyctophilus pulse interval >95ms and initial slope < 300 OPS. Often with 2 changes of frequency in the lower half. Calls usually fragmentary due to quiet calling.
- Myotis with a central kink at 47-50kHz, often with a gap when flying over water, pulse interval <75ms and initial slope > 400 OPS. Pulse angles tend to change from pulse to pulse, making a messy looking call sequence.
I have really enjoyed the Myotis discussions here in the past. So I thought I would throw what i think are Nyctophilus sequences in to see what other people think and to learn some more.The calls are really good quality and I think that they are Nyctophilus (lower kinks, not messy pulses, site not close to good Myotis habitat). But there are lots of pulse intervals of <75ms and initial slopes of 400 OPS that are meant to be more features of Myotis. Is this just due to the higher quality of the calls than we typically get from Nyctophilus (ie the detector is not missing lots of the pulses).Or are the calls not from Nyctophilus / Myotis at all? Are they an excited call from Scoteanax rueppellii / Scotorepens orion / Falsistrellus tasmaniensis? I think that this is unlikely as the pulses are not extremely close together like you get with an excited call.Anyway food for thought!AM
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Chris Corben
Feb 11, 2018, 11:16:56 AM2/11/18
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Hi Anna
I think it is perfectly reasonable to be troubled as to why these aren't Nyctophilus. In my view, the sequences are too consistent in showing such a tendency to "hook" at the bottom and the extent of that hooking is greater than I expect in NYsp, so the minimum slope of a call is lower than in NYsp. I wouldn't expect Nyctophilus to keep doing that for long, but that depends on how you chose these. For example, if there were lots of normal Nyctophilus and you just chose these because they looked different, then that is a very different situation to if these were the whole set of calls you thought fitted with NYsp. It is a probability game!
Assuming these are representative of what was going on there, I would say you are definitely looking at one of SCOR, SCRU or FATA. These three are hard to tell apart and these files could fit any of them. I don't know which of those you might get at Somersby. Visual observations can easily separate SCOR from the bigger species (with experience!), but telling SCRU from FATA, or any of them from acoustics only, is not easy, with a great deal of overlap.
Just want to clarify some of the issues around the types of calls being emitted. None of these files looks like a bat leaving a roost, though they could be close to a roost. When a bat leaves a roost, it will typically show a progression from very high clutter calls at a high Pulse Repetition Rate (PRR), to calls more typical of their usual hunting behaviour, though this depends very much on circumstances and differs a lot between species. But the features which make you speak of "excited" and clutter are results of how far a bat is flying from objects which reflect echoes back to it. They have nothing to do with habitat - but only with where a bat is flying in relation to the structures in its habitat. So you could have the most open habitat possible, but if the bat is flying close to the ground, it will still be in high clutter. OK, then you could say its habitat is close to the ground instead of in open space, but we usually think of habitat in a broader sense. So a SCRU can be in a rainforest, but flying in quite open situations such as along creeks or roadways.
Secondly, it is important to remember that search phase does not define a call type, but a whole continuum of call types depending on clutter. The calls you have posted are not typical of a SCRU/SCOR/FATA in low clutter - those would reach lower slopes and have longer durations. But if they were given by Nyctophilus, those call types would represent what that genus does when flying completely in the open. In general, I find that species which tend to hunt in higher clutter also tend to produce steeper, shorter calls when flying in the open (zero clutter) than those which tend to hunt more in the open. Rules are only meant to be broken, of course, but if we knew the level of clutter in which a bat was flying, it would often help to resolve some of these thorny ID issues. This is an important reason why bats recorded passively are harder to ID than bats which are being recorded while they are being watched - that contextual information is simply not available in passive recordings.
In your case, the bat/s are clearly giving a range of call shapes and PRR values, and so are clearly moving in and out of clutter. That could just mean flying straight along a road but passing closer to trees at some points. My suggestion is that calls like these would likely only be given by Nyctophilus in very open situations, and if you were seeing this much variation in clutter in Nyctophilus, you would also be seeing a wider range of call types, including many which were more obviously typical of Nyctophilus. The range of call types in these sequences is pretty typical for the SCOR/SCRU/FATA trio.
Also, in case the thought occurred, these are not Chalinolobus gouldii in clutter - even in relatively low clutter for CHGO, their intial sweep slopes would be much higher.
Cheers, Chris.
I think it is perfectly reasonable to be troubled as to why these aren't Nyctophilus. In my view, the sequences are too consistent in showing such a tendency to "hook" at the bottom and the extent of that hooking is greater than I expect in NYsp, so the minimum slope of a call is lower than in NYsp. I wouldn't expect Nyctophilus to keep doing that for long, but that depends on how you chose these. For example, if there were lots of normal Nyctophilus and you just chose these because they looked different, then that is a very different situation to if these were the whole set of calls you thought fitted with NYsp. It is a probability game!
Assuming these are representative of what was going on there, I would say you are definitely looking at one of SCOR, SCRU or FATA. These three are hard to tell apart and these files could fit any of them. I don't know which of those you might get at Somersby. Visual observations can easily separate SCOR from the bigger species (with experience!), but telling SCRU from FATA, or any of them from acoustics only, is not easy, with a great deal of overlap.
Just want to clarify some of the issues around the types of calls being emitted. None of these files looks like a bat leaving a roost, though they could be close to a roost. When a bat leaves a roost, it will typically show a progression from very high clutter calls at a high Pulse Repetition Rate (PRR), to calls more typical of their usual hunting behaviour, though this depends very much on circumstances and differs a lot between species. But the features which make you speak of "excited" and clutter are results of how far a bat is flying from objects which reflect echoes back to it. They have nothing to do with habitat - but only with where a bat is flying in relation to the structures in its habitat. So you could have the most open habitat possible, but if the bat is flying close to the ground, it will still be in high clutter. OK, then you could say its habitat is close to the ground instead of in open space, but we usually think of habitat in a broader sense. So a SCRU can be in a rainforest, but flying in quite open situations such as along creeks or roadways.
Secondly, it is important to remember that search phase does not define a call type, but a whole continuum of call types depending on clutter. The calls you have posted are not typical of a SCRU/SCOR/FATA in low clutter - those would reach lower slopes and have longer durations. But if they were given by Nyctophilus, those call types would represent what that genus does when flying completely in the open. In general, I find that species which tend to hunt in higher clutter also tend to produce steeper, shorter calls when flying in the open (zero clutter) than those which tend to hunt more in the open. Rules are only meant to be broken, of course, but if we knew the level of clutter in which a bat was flying, it would often help to resolve some of these thorny ID issues. This is an important reason why bats recorded passively are harder to ID than bats which are being recorded while they are being watched - that contextual information is simply not available in passive recordings.
In your case, the bat/s are clearly giving a range of call shapes and PRR values, and so are clearly moving in and out of clutter. That could just mean flying straight along a road but passing closer to trees at some points. My suggestion is that calls like these would likely only be given by Nyctophilus in very open situations, and if you were seeing this much variation in clutter in Nyctophilus, you would also be seeing a wider range of call types, including many which were more obviously typical of Nyctophilus. The range of call types in these sequences is pretty typical for the SCOR/SCRU/FATA trio.
Also, in case the thought occurred, these are not Chalinolobus gouldii in clutter - even in relatively low clutter for CHGO, their intial sweep slopes would be much higher.
Cheers, Chris.
-- Chris Corben.
BitBatty
Feb 11, 2018, 6:06:40 PM2/11/18
to Australasian bat call group
Hi Chris
Thanks so much for your detailed and very informative response. I promise to never think about 'clutter' in the same clutter / no clutter way!
The calls were all of the ones around that frequency that were recorded during the stag watch (a couple of hours). There weren't any typical Nyctophilus calls in there. So you are right in assuming these are typical of what was happening at the site, rather than strange calls in amongst typicaly Nyto calls.
The comments about bats leaving roosts progressing from high pulse repetition to normal calls, rather than these sequences that contain a range of call shapes and pulse repetition.
Thanks again for giving me tonnes to think about when looking at my next batch of bat calls.
AM
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