Is call detection rate a reliable proxy for relative abundance?

Question

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. However, there are no ground-truthed data for validation nor relevant references.

Answer 1

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:

Abrahams, 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

Answer 2

The theory to estimate density from detected sounds is clealy laid down (see e.g. Marques et al. 2013), 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 Marques et al. 2009, Marques et al. 2011 and Sébastian-González 2018. 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".

Answer 3

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

Answer 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 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.

Answer 5

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.

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

Answer 6

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 7

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).