Attack and feeding calls to differentiate genera?

[Michael Pennay]

Hi, 

I remember some time ago someone talking about how they observed different genera used different approach/attack type calls.  

I was wondering if  anyone had experience or advice on this?  

Im trying  to find ways differentiate Miniopterus tristis from Pipistrellus angulatus in Solomon Islands. 

Thanks

Michael 

[Chris Corben]

Hi Michael

See:

Corben, Chris. 2010. Feeding Buzzes. The Australasian Bat Society Newsletter 35: 40 - 44.

PDF attached.

I have no experience with tristis, but with several other species, and all have shown this distinction. In general, I find Miniopterus can closely resemble other genera in calls (eg Pipistrellus or Vespadelus)  but some subset of their calls are usually quite distinctive, typically with longer duration and calls which don't drop right down to zero slope (so still dropping in frequency somewhat at lowest slope).  Small species like australis, with their high frequency calls, tend to differ in other ways, with their longest duration calls not being so long, but they still show the distinctive feeding buzzes. However, feeding buzzes aren't always easy to come by in Miniopterus. Sometimes they do it a lot, but it is also common to see lots of sequences without buzzes.

Visually, Miniopterus look larger than the species which are similar in echolocation, with much faster looking flight, narrower pointed wings and long tails, and all the species I have seen have been dull in  colour, almost uniform but for a darker head. But they are hard to watch in flight, as they are very fast and manoevrable, especially the small species. The larger ones can be easy to watch when hunting around streetlights.


Cheers, Chris.

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Chris Corben.

[Michael Pennay]

Thanks Chris, that's very interesting- and much appreciated.

I certainly agree about  identifying Miniopterus on the wing, they are very fast (and relatively large), watching them its hard to fathom how their echolocation calls can closely resemble something small and fluttery like Vespadelus vulturnus.

One of the things I have noticed, both with Pipistrellus and Vespadelus where they overlap with Miniopterus is that these behavioral differences are sometimes visible in sequences. Eg a 'pass' of Miniopterus is just that, a pass, its in and out of detector range in one pass but Vespadelus and Pipistrelle 'passes' are sometimes long with multiple doppler effects reflecting the close circling foraging pattern of the sepecies (for example this 15 second Pipistrellus sequence)

​

Another thing I have noticed in full spectrum calls, which is similar and may be related to your observation about Miniopterus calls not flattening out, is that the maximum amplitude in Miniopterus calls is often (not always) in the middle to tail end of the call pulse, whereas in most Vespadelus (and Pipistrellus that I have seen) calls the maximum amplitude usually around the 'knee' or just after, but rarely towards the tail. Have you noticed this?

Thanks again

Michael

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[Michael Pennay]

Here's an example of what I was talking about using Miniopterus oceanensis and Vespadelus vulturnus calls from southern tablelands on NSW where they overlap almost completely in many call characteristics.

You can see max amplitude in the Miniopterus is later than Vespadelus and Vespadelus has more energy in the downsweep, which gives them different time/amplitude patterns.

Both species use both types of calls, but the pattern of most energy in the latter part and not so much in the downsweep is much more common in Miniopterus,

Vespadelus usually seem to be loudest in the middle of the flattest part  or at the knee.
​

[Chris Corben]

Hi Michael

That's interesting and no, I haven't noticed it. But don't have too many FS recordings of Aus bats. I note in your two examples, that there are a couple of other things going on. The initial downsweep (neck) is steeper and more abruptly separated from the body in the VEVU and I wonder if that might correlate with the amplitude display? It would be interesting if the differences you see are due to a difference in the frequency with which the two genera produce pulses with a sharper transition from neck to body. I also note that in many genera, there seems to be a relationship between the initial slope and the lowest slope achieved. You can see this effect if you compare CHGO (steep neck, low slope body) with FATA (less steep neck, but not tending to be so flat in the body). Also, it has intrigued me that Miniopterus typically show more slope in the longest duration pulses while shorter pulses are often more Vespadelus like and tend to hook round more at the bottom. Not sure that helps ID much, since the biggest problem is the shorter calls of Miniopterus and the longer calls of Vespadelus. 

I assume you are talking about the amplitude as judged by the oscillogram at the bottom of the screen?

Just to be pedantic, the oscillogram shows the amplitude, which may be significantly altered from what the bat emitted (eg due to overlapping echoes). On the other hand, the energy content is shown by the colour of the trace in the spectrogram. The difference can be important, because the energy content is a function of both the amplitude and the slope. Energy involves time, so the longer a signal spends in the same frequency range, the higher the energy content.

Cheers, Chris.

On 5/15/2017 12:13 AM, Michael Pennay wrote:

Here's an example of what I was talking about using Miniopterus oceanensis and Vespadelus vulturnus calls from southern tablelands on NSW where they overlap almost completely in many call characteristics.

You can see max amplitude in the Miniopterus is later than Vespadelus and Vespadelus has more energy in the downsweep, which gives them different time/amplitude patterns.

Both species use both types of calls, but the pattern of most energy in the latter part and not so much in the downsweep is much more common in Miniopterus,

Vespadelus usually seem to be loudest in the middle of the flattest part  or at the knee.
​

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Chris Corben.