It is not just about birds: what do acoustic indices reveal about a Costa Rican tropical rainforest?

Figures & data

Figure 1. Location of “Ceibo” and “Quebrada” study sites within the Braulio Carrillo National Park, Costa Rica, 2017–2018

Table 1. Description of bird and acoustic indices calculated for each sampling point at Ceibo and Quebrada sites, Braulio Carrillo National Park, Costa Rica, 2017–2018

Bird indices	Description
Abundance	Number of individuals from all species
Richness	Number of species
Shannon	Shannon diversity index [35]
Pielou	Evenness of Pielou [36]
Acoustic Indices	Description
ACI	Acoustic Complexity Index [9].
ADI	Acoustic Diversity Index [10].
AEI	Acoustic Evenness Index [10].
BIO	Bioacustic Index [15].
MAE	Median Amplitude Envelope [18].
NDSI	Normalized Difference Soundscape Index [11].
NP	Number of Peaks [14].
Hf	Spectral Entropy [3]
Ht	Temporal Entropy [3]
TE	Total Entropy [3]
SPLMean	Mean Sound Pressure Level

Figure 2. Correlation analysis of acoustic indices and bird indices at Ceibo and Quebrada sites, Braulio Carrillo National Park, Costa Rica, 2017–2018

Figure 3. Normalized mean absolute error (nmae), coefficient of determination (rsquared), and normalized root mean square error (nrmse) for random forest regression on four bird indices (abundance, richness, Pielou Evenness Index, and Shannon Diversity Index) at Ceibo and Quebrada sites, Braulio Carrillo National Park, Costa Rica, 2017–2018

Figure 4. Variable importance for random forest regression on four bird indices (abundance, richness, Pielou Evenness Index, and Shannon Diversity Index) at Ceibo and Quebrada sites, Braulio Carrillo National Park, Costa Rica, 2017–2018

Figure 5. Variable importance for the random forest classifier for two sites with two different level of anthropogenic perturbation based on 11 acoustic indices at Ceibo and Quebrada sites, Braulio Carrillo National Park, Costa Rica, 2017–2018

Table

Acoustic indices	Code	Description
Acoustic Complexity Index.	ACI	Measures the variability of sound intensity over time and frequency [9]. Higher values indicate more complex soundscapes. Range = [0, +].
Acoustic Diversity Index.	ADI	Summarizes sound intensity distribution applying the Shannon index over the proportion of signals above an intensity threshold across the spectrum [10]. Higher values indicate that acoustic energy is spread evenly across frequency bands. Range = [0, +].
Acoustic Evenness Index.	AEI	Same as the ADI, but the Gini index is applied across all frequency bins, instead of the Shannon index [10]. High values indicate acoustic energy is restricted to a narrow frequency range. Range = [0, 1].
Bioacoustic Index.	BIO	It is a function of both amplitude and number of occupied frequency bands between 2–11 kHz. It is calculated as the area under each curve included all frequency bands between 2–11 kHz associated with the dB value that was greater than the minimum dB value for each curve. Higher values indicate greater disparity between bands [15]. Range = [0, +].
Median Amplitude Envelope.	MAE	The median of the amplitude envelope normalized by the maximum value to give results between 0–1. Higher values reflect noisier soundscapes [18]. Range = [0, 1]
Normalized Difference Soundscape Index	NDSI	The ratio (biophony − anthrophony)/(biophony + anthrophony). Where biophony is the energy on the frequency range 2–8 kHz and anthrophony between 1–2 kHz [11]. Higher values indicate a higher proportion of acoustic energy in the biophony band. Range = [−1, 1].
Number of Peaks	NP	Counts the number of major frequency peaks obtained on a mean spectrum. Higher values indicates a greater frequency spectral complexity [14]. Range = [0, +].
Spectral Entropy	Hf	Divides intensity values by the sum of intensity in a frequency band. Calculates the entropy for these values using the negative sum of each value multiplied by the log of the value and divided by the log of the number of intensity values [3]. Higher values indicate evenly distributed sound across frequency bands. Range = [0, 1].
Temporal Entropy	Ht	Divide the intensity values by the sum of intensities in a time interval. Calculates entropy for these values using the negative sum of each value multiplied by the log of the value and divided by the log of the number of intensity values [3]. Higher values indicate evenly distributed sound over time. Range = [0, 1].
Total Entropy.	TE	It is the product of Hf * Ht. Quantifies the entropy across time and frequency [3]. Higher values indicate evenly distributed sounds across frequency and time. Range = [0, 1].
Mean Sound Pressure Level	SPLMean	Calculates the average sound pressure level in dB, using a decibel reference value of 2 × 10–5 Pa. Higher values indicate louder soundscapes. Range = [0, +].

Table

Species	Ceibo	Quebrada
Accipitridae
Harpagus bidentatus	x
Pseudastur albicollis	x
Alcedinidae
Chloroceryle americana		x
Bucconidae
Malacoptila panamensis		x
Capitonidae
Eubucco bourcierii		x
Caprimulgidae
Nyctidromus albicollis		x
Cardinalidae
Caryothraustes poliogaster	x	x
Chlorothraupis carmioli	x	x
Cyanoloxia cyanoides	x	x
Habia fuscicauda	x	x
Piranga flava		x
Piranga rubra		x
Saltator grossus	x	x
Saltator maximus		x
Cathartidae
Sarcoramphus papa		x
Columbidae
Geotrygon montana		x
Leptotila cassinii		x
Leptotila verreauxi	x
Leptotrygon veraguensis		x
Patagioenas fasciata		x
Patagioenas nigrirostris	x	x
Zentrygon lawrencii	x	x
Corvidae
Psilorhinus morio		x
Cotingidae
Lipaugus unirufus	x	x
Cracidae
Crax rubra		x
Penelope purpurascens		x
Cuculidae
Piaya cayana	x	x
Falconidae
Falco rufigularis	x
Micrastur ruficollis		x
Formicariidae
Formicarius analis		x
Fringillidae
Euphonia anneae	x	x
Euphonia gouldi	x	x
Furnariidae
Automolus ochrolaemus	x	x
Automolus subulatus		x
Dendrocincla fuliginosa		x
Glyphorynchus spirurus	x	x
Lepidocolaptes souleyetii	x
Sclerurus mexicanus		x
Sittasomus griseicapillus		x
Xenops minutus		x
Xiphorhynchus erythropygius	x	x
Xiphorhynchus lachrymosus	x
Xiphorhynchus susurrans	x	x
Grallaridae
Hylopezus dives	x	x
Hylopezus perspicillatus	x	x
Icteridae
Cacicus uropygialis	x	x
Dives dives		x
Icterus galbula		x
Psarocolius montezuma	x	x
Psarocolius wagleri	x	x
Mitrospingidae
Mitrospingus cassinii	x	x
Momotidae
Baryphthengus martii		x
Electron platyrhynchum	x	x
Onychorhynchidae
Myiobius sulphureipygius		x
Terenotriccus erythrurus		x
Oxyruncidae
Oxyruncus cristatus		x
Parulidae
Myiothlypis fulvicauda		x
Oreothlypis peregrina		x
Setophaga castanea		x
Setophaga pensylvanica	x	x
Setophaga pitiayumi		x
Vermivora chrysoptera	x
Passerellidae
Arremon aurantiirostris	x	x
Arremonops conirostris		x
Picidae
Campephilus guatemalensis	x
Celeus loricatus	x	x
Melanerpes pucherani	x	x
Piculus simplex	x	x
Pipridae
Corapipo altera	x	x
Manacus candei		x
Polioptilidae
Microbates cinereiventris	x	x
Polioptila plumbea		x
Ramphocaenus melanurus	x	x
Psittacidae
Amazona autumnalis	x	x
Amazona farinosa	x	x
Ara ambiguus	x
Pionus senilis	x	x
Psittacara finschi		x
Pyrilia haematotis	x	x
Ramphastidae
Pteroglossus torquatus	x	x
Ramphastos ambiguus	x	x
Ramphastos sulfuratus	x	x
Selenidera spectabilis	x	x
Thamnophilidae
Cercomacroides tyrannina	x
Dysithamnus mentalis		x
Dysithamnus striaticeps	x	x
Epinecrophylla fulviventris		x
Gymnocichla nudiceps		x
Gymnopithys bicolor	x	x
Hylophylax naevioides		x
Microrhopias quixensis	x	x
Myrmotherula axillaris	x	x
Myrmotherula schisticolor		x
Phaenostictus mcleannani	x	x
Poliocrania exsul	x	x
Sipia laemosticta	x	x
Thamnistes anabatinus	x	x
Thamnophilus atrinucha		x
Thraupidae
Bangsia arcaei		x
Chlorophanes spiza	x	x
Chrysothlypis chrysomelas		x
Coereba flaveola		x
Cyanerpes cyaneus		x
Cyanerpes lucidus		x
Lanio leucothorax		x
Ramphocelus passerinii		x
Tachyphonus delatrii	x	x
Tachyphonus luctuosus	x	x
Tachyphonus rufus		x
Tangara florida		x
Tangara gyrola		x
Tangara icterocephala	x	x
Tangara inornata		x
Threskiornithidae
Mesembrinibis cayennensis		x
Tinamidae
Crypturellus boucardi	x
Tinamus major	x	x
Tityridae
Pachyramphus cinnamomeus		x
Trochilidae
Campylopterus hemileucurus	x
Chalybura urochrysia	x	x
Florisuga mellivora		x
Glaucis aeneus	x
Heliothryx barroti		x
Klais guimeti		x
Phaethornis guy	x	x
Phaethornis longirostris	x	x
Phaethornis striigularis	x	x
Thalurania colombica	x	x
Threnetes ruckeri		x
Troglodytidae
Campylorhynchus zonatus	x	x
Cantorchilus nigricapillus	x
Cantorchilus thoracicus	x	x
Cyphorhinus phaeocephalus		x
Henicorhina leucosticta	x	x
Microcerculus philomela	x	x
Pheugopedius atrogularis	x
Trogonidae
Trogon caligatus	x	x
Trogon clathratus	x
Trogon massena	x
Trogon rufus	x	x
Turdidae
Catharus mexicanus	x	x
Catharus minimus		x
Catharus ustulatus		x
Hylocichla mustelina	x	x
Turdus grayi		x
Turdus obsoletus		x
Turdus plebejus		x
Tyrannidae
Attila spadiceus	x	x
Contopus virens	x
Empidonax flaviventris	x	x
Empidonax virescens		x
Megarynchus pitangua	x	x
Mionectes oleagineus		x
Mionectes olivaceus		x
Myiarchus crinitus	x
Myiarchus tuberculifer		x
Myiornis atricapillus	x
Myiozetetes granadensis		x
Myiozetetes similis		x
Oncostoma cinereigulare		x
Pitangus sulphuratus	x	x
Platyrinchus coronatus		x
Rhytipterna holerythra	x	x
Todirostrum nigriceps		x
Tolmomyias sulphurescens	x	x
Tyrannus melancholicus		x
Zimmerius vilissimus	x	x
Vireonidae
Pachysylvia decurtata	x	x
Vireo olivaceus	x	x
Vireolanius pulchellus	x

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