<p>The theory to estimate density from detected sounds is clealy laid down (see e.g. <a href="https://onlinelibrary.wiley.com/doi/10.1111/brv.12001" rel="noreferrer">Marques et al. 2013</a>), and if you go for a cue counting apporach, you can estimate a density of calls and then convert that into a density of animals. But to do so you need to account for at least 3 factors: (1) detectability (2) detector performance like false positives (3) call rate. Some examples where this was done are <a href="https://asa.scitation.org/doi/10.1121/1.3089590" rel="noreferrer">Marques et al. 2009</a>, <a href="https://www.int-res.com/abstracts/esr/v13/n3/p163-172/" rel="noreferrer">Marques et al. 2011</a> and <a href="https://www.ace-eco.org/vol13/iss2/art7/" rel="noreferrer">Sébastian-González 2018</a>. Trully sorry for the blattant self promotion of my work, would be great to get some additional examples here from other folks out there!</p>
<p>An important tangent: I would be very careful when referring to the number of detected calls on sensors as a &quot;call rate&quot;. At best, a &quot;detected call rate&quot; or some such. Why am I saying this? A &quot;call rate&quot; should be the number of sounds produced by an animal per unit time. And in fact that &quot;call rate&quot; is one of the multipliers you require to estimate density from detected calls on sensors. What you call those counts becomes a matter of debate, but &quot;call rate&quot; is misleading because a &quot;call rate&quot; should apply to an animal, and when you are looking at detections on a sensor, these could be from many animals, or from a single animal with many calls from that animal being missed, so in neither way an animal &quot;call rate&quot;.</p>

CC BY-SA 4.0
2022-07-05T14:09:54.600Z
This is incredibly insightful and I appreciate you sharing your work. Thank you. I am making use of intermittent sampling (randomly assembled 5-min samples and 50 samples in total per site), and was contemplating using the detection of a species' call per sample as a potential measure of relative abundance at a given site.
Frowin Becker
CC BY-SA 4.0
2022-07-07T00:49:03.810Z
+1 for "detection rate" instead of "call rate!"
selene
CC BY-SA 4.0
2022-07-05T10:02:03.273Z
2022-07-05T10:02:03.273Z
Tiago Marques
<p>Above papers nicely capture some of the key information. Things to keep an eye out for are:</p>
<ul>
<li>variations in call rate of the species due to time of year, location, time of day, weather etc</li>
<li>individual differences in call rate (variation)</li>
<li>measure your detection area for the recorder so that you can estimate how close to the recorder calling birds are</li>
<li>different habitats might also lead to different signal transmission rates, both from the source (ie impact calling behaviour) through to detection (e.g. propagation).</li>
</ul>
<p>In short there are lots of things that might vary and impact your ability to do this, but with care they are all measurable and you can estimate their importance. Sometimes you get lucky and it can be a simple equation like we were with bell miners as per below, other times it is a little trickier. Lots of other examples here to review as well that are more detailed. Good luck!
<a href="https://www.researchgate.net/profile/Kathryn-Lambert/publication/261872461_A_low-cost_yet_simple_and_highly_repeatable_system_for_acoustically_surveying_cryptic_species/links/5a56923baca272bb6963f181/A-low-cost-yet-simple-and-highly-repeatable-system-for-acoustically-surveying-cryptic-species.pdf" rel="noreferrer">https://www.researchgate.net/profile/Kathryn-Lambert/publication/261872461_A_low-cost_yet_simple_and_highly_repeatable_system_for_acoustically_surveying_cryptic_species/links/5a56923baca272bb6963f181/A-low-cost-yet-simple-and-highly-repeatable-system-for-acoustically-surveying-cryptic-species.pdf</a></p>

CC BY-SA 4.0
2022-07-07T08:13:29.973Z
Thank you for this contribution!
Frowin Becker
CC BY-SA 4.0
2022-07-06T22:30:27.940Z
2022-07-06T22:30:27.940Z
Paul McDonald
<p>There are also these papers:</p>
<p>Acoustic estimation of wildlife abundance: methodology for vocal mammals in forested habitats. <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2028.2009.01161.x" rel="noreferrer">https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2028.2009.01161.x</a></p>
<p>Assessment of cue counting for estimating bird density using passive acoustic monitoring: recommendations for estimating a reliable cue rate. <a href="https://www.ace-eco.org/vol16/iss1/art11/" rel="noreferrer">https://www.ace-eco.org/vol16/iss1/art11/</a></p>
<p><a href="https://www.researchgate.net/profile/Kathryn-Lambert/publication/261872461_A_low-cost_yet_simple_and_highly_repeatable_system_for_acoustically_surveying_cryptic_species/links/5a56923baca272bb6963f181/A-low-cost-yet-simple-and-highly-repeatable-system-for-acoustically-surveying-cryptic-species.pdf" rel="noreferrer">A low-cost, yet simple and highly repeatable system for
acoustically surveying cryptic species</a>.</p>
<p>Estimating abundance of the Stripeless tree-frog Hyla meridionalis by means of replicated call counts. <a href="https://www.researchgate.net/publication/338233493_Estimating_abundance_of_the_Stripeless_tree-frog_Hyla_meridionalis_by_means_of_replicated_call_counts" rel="noreferrer">https://www.researchgate.net/publication/338233493_Estimating_abundance_of_the_Stripeless_tree-frog_Hyla_meridionalis_by_means_of_replicated_call_counts</a></p>
<p>Identifying and predicting occurrence and abundance of a vocal animal species based on individually specific calls. <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.3685" rel="noreferrer">https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.3685</a></p>
<p>Estimating Streaked Shearwater Calonectris leucomelas abundance in the Republic of Korea using automated acoustic recorders. <a href="http://www.marineornithology.org/content/get.cgi?rn=1406" rel="noreferrer">http://www.marineornithology.org/content/get.cgi?rn=1406</a></p>
<p>A spatial capture–recapture model to estimate call rate and population density from passive acoustic surveys. <a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/2041-210X.13522" rel="noreferrer">https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/2041-210X.13522</a></p>

CC BY-SA 4.0
2022-08-05T18:17:05.713Z
Hi Carly, could you give a summary of the most relevant paper(s) that allow to respond to Frowin's question please?
Noil
CC BY-SA 4.0
2022-07-06T17:32:20.543Z
Thank you for this.
Frowin Becker
CC BY-SA 4.0
2022-07-06T16:34:17.217Z
2022-07-06T16:34:17.217Z
Carly Batist
<p>What you may need to consider is if you can determine how many individuals are calling. A major hurtle, especially if your recording sites only have single sensors, is assurance that your recorded calls are coming from a single individual. However, if you can make some assumptions about group size based on territorial behavior (i.e. males having a nesting region that they only allow females access to), there are some paths.</p>
<p><a href="https://onlinelibrary.wiley.com/doi/full/10.1111/mms.12872?casa_token=DtcjakRUiC4AAAAA%3AiO8-qF4P7fQEGCfE71ma9hO1H_4rVcb7jG-4z9OtntkrPHbV3vO9ZHlVsy4ufCSEpif42Pm9z5MjyXJscA" rel="nofollow noreferrer">Barlow et al. 2022</a> uses a Bayesian approach, from multiple arrays of two sensors. Because of the two sensors, we were able to determine the declination angle, and thereby get an estimate of how many individuals were echolocating. We backed this up with historical comparitive visual survey data.</p>
<p>Our approach is based, though, on point-transects and the 'snapshot' survey method. Which originally came from the bird world, I believe. :)</p>
<p><strong>Reference</strong></p>
<p>Barlow, J., Moore, J. E., McCullough, J. L., &amp; Griffiths, E. T. (2022). Acoustic‐based estimates of Cuvier's beaked whale (Ziphius cavirostris) density and abundance along the US West Coast from drifting hydrophone recorders. Marine Mammal Science, 38(2), 517-538.</p>

CC BY-SA 4.0
2022-07-04T08:57:48.770Z
Thank you for this. In my case, it would only be relevant for single sensors.
Frowin Becker
CC BY-SA 4.0
2022-07-04T15:14:52.793Z
Again, if you can make some educated assumptions about group size based on call rate, you have more to work with. :)
etgriffiths
CC BY-SA 4.0
2022-07-04T06:29:59.837Z
2022-07-04T06:29:59.837Z
etgriffiths
<p>Other answers have already given lots of links, but I recently came across this brand new forum piece in Ibis from Wood &amp; Peery &quot;What does ‘occupancy’ mean in passive acoustic surveys?&quot; <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/ibi.13092" rel="nofollow noreferrer">https://onlinelibrary.wiley.com/doi/full/10.1111/ibi.13092</a></p>
<p>They raise some critical points about study design and (lack of) comparability among studies.</p>

CC BY-SA 4.0
2022-07-07T08:04:37.277Z
2022-07-07T08:04:37.277Z
EcologyTom
<p>It can be, but it depends. Most of these use cases at least in my experience have involved ground-truthed data to some extent (that is, get a call rate and determine its correlation to point counts, burrow grubbing, etc and then move forward using that call rate alone in subsequent years if it's a reliable indicator).</p>

CC BY-SA 4.0
2022-07-04T05:08:15.827Z
Are there any of these cases that you could share a link to? I guess, I am rather looking for justification to include it in my analysis.
Frowin Becker
CC BY-SA 4.0
2022-07-03T17:47:20.020Z
2022-07-03T17:47:20.020Z
dtsavage
<p>in relation to birds and call rates you should probably check out the following papers, especially the work of Cristian Pérez-Granados:</p>
<blockquote>
<p>Vocal activity rate index: a useful method to infer terrestrial bird
abundance with acoustic monitoring C Pérez‐Granados, G Bota, D Giralt,
A Barrero, J Gómez‐Catasús, ... Ibis 161 (4), 901-907</p>
<p>Effort needed to accurately estimate Vocal Activity Rate index using
acoustic monitoring: A case study with a dawn-time singing passerine C
Pérez-Granados, J Gómez-Catasús, D Bustillo-de la Rosa, A Barrero, ...
Ecological Indicators 107, 105608</p>
<p>Arneill, G.E., Critchley, E.J., Wischnewski, S., Jessopp, M.J. and
Quinn, J.L. (2020), Acoustic activity across a seabird colony reflects
patterns of within-colony flight rather than nest density. Ibis, 162:
416-428. <a href="https://doi.org/10.1111/ibi.12740" rel="noreferrer">https://doi.org/10.1111/ibi.12740</a></p>
<p>BORKER, A.L., MCKOWN, M.W., ACKERMAN, J.T., EAGLES-SMITH, C.A.,
TERSHY, B.R. and CROLL, D.A. (2014), Vocal Activity as a Low Cost and
Scalable Index of Seabird Colony Size. Conservation Biology, 28:
1100-1108. <a href="https://doi.org/10.1111/cobi.12264" rel="noreferrer">https://doi.org/10.1111/cobi.12264</a></p>
<p>Oppel S, Hervias S, Oliveira N, Pipa T, Silva C, Geraldes P, Goh M,
Immler E, McKown M (2014) Estimating population size of a nocturnal
burrow-nesting seabird using acoustic monitoring and habitat mapping.
Nature Conservation 7: 1-13.
<a href="https://doi.org/10.3897/natureconservation.7.6890" rel="noreferrer">https://doi.org/10.3897/natureconservation.7.6890</a></p>
</blockquote>
<p>And if you are desperate, then maybe my work on capercaillie:</p>
<blockquote>
<p>Abrahams, C. Comparison between lek counts and bioacoustic recording for monitoring Western Capercaillie (Tetrao urogallus L.). J Ornithol 160, 685–697 (2019). <a href="https://doi.org/10.1007/s10336-019-01649-8" rel="noreferrer">https://doi.org/10.1007/s10336-019-01649-8</a></p>
</blockquote>

CC BY-SA 4.0
2022-08-05T18:14:14.710Z
Hi Carlos, could you give a summary of the most relevant paper(s) that allow to respond to Frowin's  question please?
Noil
CC BY-SA 4.0
2022-07-05T13:57:57.373Z
Oh, this is absolutely brilliant. Thanks so much!
Frowin Becker
CC BY-SA 4.0
2022-07-05T12:01:14.490Z
2022-07-05T12:01:14.490Z
Carlos Abrahams
<p>I have been busy analyzing bird community data from close to 50 different sites in an urban forest matrix, but have only been making use of presence-absence. Are there any resources available that assess the utility of call detection rates as a relative abundance measure in community ecology (i.o.w. for multiple species)? I have found them hard, if not impossible, to come by.</p>
<p>A reference I can present is the methodology used in Chapter 4 of this <a href="https://researcharchive.vuw.ac.nz/xmlui/handle/10063/32/browse?type=author&amp;value=Fea%2C+Iona+Nyree" rel="noreferrer">doctoral dissertation</a>. However, there are no ground-truthed data for validation nor relevant references.</p>

CC BY-SA 4.0
2022-07-04T07:39:47.593Z
Could you please share work done on your own initiative (references, method names) and/or talk of why the existing methods are 'hard, if not impossible, to come by'. This will provide background for answers to come.
Thejasvi
CC BY-SA 4.0
2022-07-04T08:48:27.943Z
That's tricky, because my own initiative hasn't really yielded anything substantial. The one reference I can present is the methodology used in this [doctoral dissertation](https://researcharchive.vuw.ac.nz/xmlui/handle/10063/32/browse?type=author&value=Fea%2C+Iona+Nyree). However, there are no ground-truthed data for validation nor relevant references.
Frowin Becker
CC BY-SA 4.0
2022-07-04T09:01:22.257Z
I have also edited the original post to include the reference. Thank you for highlighting this.
Frowin Becker
<community>
Is call detection rate a reliable proxy for relative abundance?
# Is call detection rate a reliable proxy for relative abundance?

(Asked by: username_0 on 2022-07-03)

I have been busy analyzing bird community data from close to 50 different sites in an urban forest matrix, but have only been making use of presence-absence. Are there any resources available that assess the utility of call detection rates as a relative abundance measure in community ecology (i.o.w. for multiple species)? I have found them hard, if not impossible, to come by.

A reference I can present is the methodology used in Chapter 4 of this [doctoral dissertation](https://researcharchive.vuw.ac.nz/xmlui/handle/10063/32/browse?type=author&value=Fea%2C+Iona+Nyree). However, there are no ground-truthed data for validation nor relevant references.

**Tags:** community

> **Comments:**
> **username_1**: Could you please share work done on your own initiative (references, method names) and/or talk of why the existing methods are 'hard, if not impossible, to come by'. This will provide background for answers to come.  
> **username_0**: That's tricky, because my own initiative hasn't really yielded anything substantial. The one reference I can present is the methodology used in this [doctoral dissertation](https://researcharchive.vuw.ac.nz/xmlui/handle/10063/32/browse?type=author&value=Fea%2C+Iona+Nyree). However, there are no ground-truthed data for validation nor relevant references.  
> **username_0**: I have also edited the original post to include the reference. Thank you for highlighting this.  

---

## 7 answers

### Answer by username_10 on 2022-07-05. Score: 8 | Accepted answer

in relation to birds and call rates you should probably check out the following papers, especially the work of Cristian Pérez-Granados:

> Vocal activity rate index: a useful method to infer terrestrial bird
> abundance with acoustic monitoring C Pérez‐Granados, G Bota, D Giralt,
> A Barrero, J Gómez‐Catasús, ... Ibis 161 (4), 901-907
>
> Effort needed to accurately estimate Vocal Activity Rate index using
> acoustic monitoring: A case study with a dawn-time singing passerine C
> Pérez-Granados, J Gómez-Catasús, D Bustillo-de la Rosa, A Barrero, ...
> Ecological Indicators 107, 105608
>
> Arneill, G.E., Critchley, E.J., Wischnewski, S., Jessopp, M.J. and
> Quinn, J.L. (2020), Acoustic activity across a seabird colony reflects
> patterns of within-colony flight rather than nest density. Ibis, 162:
> 416-428. <https://doi.org/10.1111/ibi.12740>
>
> BORKER, A.L., MCKOWN, M.W., ACKERMAN, J.T., EAGLES-SMITH, C.A.,
> TERSHY, B.R. and CROLL, D.A. (2014), Vocal Activity as a Low Cost and
> Scalable Index of Seabird Colony Size. Conservation Biology, 28:
> 1100-1108. <https://doi.org/10.1111/cobi.12264>
>
> Oppel S, Hervias S, Oliveira N, Pipa T, Silva C, Geraldes P, Goh M,
> Immler E, McKown M (2014) Estimating population size of a nocturnal
> burrow-nesting seabird using acoustic monitoring and habitat mapping.
> Nature Conservation 7: 1-13.
> <https://doi.org/10.3897/natureconservation.7.6890>

And if you are desperate, then maybe my work on capercaillie:

> username_10, C. Comparison between lek counts and bioacoustic recording for monitoring Western Capercaillie (Tetrao urogallus L.). J Ornithol 160, 685–697 (2019). <https://doi.org/10.1007/s10336-019-01649-8>

> **Comments:**
> **username_0**: Oh, this is absolutely brilliant. Thanks so much!  
> **username_6**: Hi username_10, could you give a summary of the most relevant paper(s) that allow to respond to username_0's  question please?  

---

### Answer by username_2 on 2022-07-05. Score: 16

The theory to estimate density from detected sounds is clealy laid down (see e.g. [username_2 et al. 2013](https://onlinelibrary.wiley.com/doi/10.1111/brv.12001)), and if you go for a cue counting apporach, you can estimate a density of calls and then convert that into a density of animals. But to do so you need to account for at least 3 factors: (1) detectability (2) detector performance like false positives (3) call rate. Some examples where this was done are [username_2 et al. 2009](https://asa.scitation.org/doi/10.1121/1.3089590), [username_2 et al. 2011](https://www.int-res.com/abstracts/esr/v13/n3/p163-172/) and [Sébastian-González 2018](https://www.ace-eco.org/vol13/iss2/art7/). Trully sorry for the blattant self promotion of my work, would be great to get some additional examples here from other folks out there!

An important tangent: I would be very careful when referring to the number of detected calls on sensors as a "call rate". At best, a "detected call rate" or some such. Why am I saying this? A "call rate" should be the number of sounds produced by an animal per unit time. And in fact that "call rate" is one of the multipliers you require to estimate density from detected calls on sensors. What you call those counts becomes a matter of debate, but "call rate" is misleading because a "call rate" should apply to an animal, and when you are looking at detections on a sensor, these could be from many animals, or from a single animal with many calls from that animal being missed, so in neither way an animal "call rate".

> **Comments:**
> **username_0**: This is incredibly insightful and I appreciate you sharing your work. Thank you. I am making use of intermittent sampling (randomly assembled 5-min samples and 50 samples in total per site), and was contemplating using the detection of a species' call per sample as a potential measure of relative abundance at a given site.  
> **username_3**: +1 for "detection rate" instead of "call rate!"  

---

### Answer by username_4 on 2022-07-06. Score: 6

Above papers nicely capture some of the key information. Things to keep an eye out for are:

* variations in call rate of the species due to time of year, location, time of day, weather etc
* individual differences in call rate (variation)
* measure your detection area for the recorder so that you can estimate how close to the recorder calling birds are
* different habitats might also lead to different signal transmission rates, both from the source (ie impact calling behaviour) through to detection (e.g. propagation).

In short there are lots of things that might vary and impact your ability to do this, but with care they are all measurable and you can estimate their importance. Sometimes you get lucky and it can be a simple equation like we were with bell miners as per below, other times it is a little trickier. Lots of other examples here to review as well that are more detailed. Good luck!
<https://www.researchgate.net/profile/Kathryn-Lambert/publication/261872461_A_low-cost_yet_simple_and_highly_repeatable_system_for_acoustically_surveying_cryptic_species/links/5a56923baca272bb6963f181/A-low-cost-yet-simple-and-highly-repeatable-system-for-acoustically-surveying-cryptic-species.pdf>

> **Comments:**
> **username_0**: Thank you for this contribution!  

---

### Answer by username_5 on 2022-07-06. Score: 4

There are also these papers:

Acoustic estimation of wildlife abundance: methodology for vocal mammals in forested habitats. <https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2028.2009.01161.x>

Assessment of cue counting for estimating bird density using passive acoustic monitoring: recommendations for estimating a reliable cue rate. <https://www.ace-eco.org/vol16/iss1/art11/>

[A low-cost, yet simple and highly repeatable system for
acoustically surveying cryptic species](https://www.researchgate.net/profile/Kathryn-Lambert/publication/261872461_A_low-cost_yet_simple_and_highly_repeatable_system_for_acoustically_surveying_cryptic_species/links/5a56923baca272bb6963f181/A-low-cost-yet-simple-and-highly-repeatable-system-for-acoustically-surveying-cryptic-species.pdf).

Estimating abundance of the Stripeless tree-frog Hyla meridionalis by means of replicated call counts. <https://www.researchgate.net/publication/338233493_Estimating_abundance_of_the_Stripeless_tree-frog_Hyla_meridionalis_by_means_of_replicated_call_counts>

Identifying and predicting occurrence and abundance of a vocal animal species based on individually specific calls. <https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.3685>

Estimating Streaked Shearwater Calonectris leucomelas abundance in the Republic of Korea using automated acoustic recorders. <http://www.marineornithology.org/content/get.cgi?rn=1406>

A spatial capture–recapture model to estimate call rate and population density from passive acoustic surveys. <https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/2041-210X.13522>

> **Comments:**
> **username_0**: Thank you for this.  
> **username_6**: Hi username_5, could you give a summary of the most relevant paper(s) that allow to respond to username_0's question please?  

---

### Answer by username_7 on 2022-07-04. Score: 4

What you may need to consider is if you can determine how many individuals are calling. A major hurtle, especially if your recording sites only have single sensors, is assurance that your recorded calls are coming from a single individual. However, if you can make some assumptions about group size based on territorial behavior (i.e. males having a nesting region that they only allow females access to), there are some paths.

[Barlow et al. 2022](https://onlinelibrary.wiley.com/doi/full/10.1111/mms.12872?casa_token=DtcjakRUiC4AAAAA%3AiO8-qF4P7fQEGCfE71ma9hO1H_4rVcb7jG-4z9OtntkrPHbV3vO9ZHlVsy4ufCSEpif42Pm9z5MjyXJscA) uses a Bayesian approach, from multiple arrays of two sensors. Because of the two sensors, we were able to determine the declination angle, and thereby get an estimate of how many individuals were echolocating. We backed this up with historical comparitive visual survey data.

Our approach is based, though, on point-transects and the 'snapshot' survey method. Which originally came from the bird world, I believe. :)

**Reference**

Barlow, J., Moore, J. E., McCullough, J. L., & Griffiths, E. T. (2022). Acoustic‐based estimates of Cuvier's beaked whale (Ziphius cavirostris) density and abundance along the US West Coast from drifting hydrophone recorders. Marine Mammal Science, 38(2), 517-538.

> **Comments:**
> **username_0**: Thank you for this. In my case, it would only be relevant for single sensors.  
> **username_7**: Again, if you can make some educated assumptions about group size based on call rate, you have more to work with. :)  

---

### Answer by username_8 on 2022-07-07. Score: 2

Other answers have already given lots of links, but I recently came across this brand new forum piece in Ibis from Wood & Peery "What does ‘occupancy’ mean in passive acoustic surveys?" <https://onlinelibrary.wiley.com/doi/full/10.1111/ibi.13092>

They raise some critical points about study design and (lack of) comparability among studies.


---

### Answer by username_9 on 2022-07-03. Score: 1

It can be, but it depends. Most of these use cases at least in my experience have involved ground-truthed data to some extent (that is, get a call rate and determine its correlation to point counts, burrow grubbing, etc and then move forward using that call rate alone in subsequent years if it's a reliable indicator).

> **Comments:**
> **username_0**: Are there any of these cases that you could share a link to? I guess, I am rather looking for justification to include it in my analysis.  

---

