Roars, Rumbles, and Resonance: A Systematic Review and Meta‐Analysis of Crocodylian Acoustic Signals

Classified as probably not a substantial claim. May combine two claims.

Multiple terms may be used for the same metric, and single terms have multiple definitions in bioacoustics in other taxa such as amphibians and birds.

“Such issues have been longstanding in the field of bioacoustics in other taxa such as amphibians and birds, whereby multiple terms may be used for the same metric, and single terms have multiple definitions (Köhler et al. 2017; Odom et al. 2021).”

• cites Köhler et al. 2017 sourceSupported
• cites Odom et al. 2021 sourcePartly supported

  The Abstract (page unavailable) advocates standardizing acoustic terminology across disciplines and taxa, supporting the general point that terminology is an issue. The retrieved copy does not specify that multiple terms name the same metric or that a single term has multiple definitions, or identify amphibians and birds in this connection. (LLM, conf=0.72)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

Standardising methodologies will avoid confusion and enable meaningful comparisons across species, populations, sexes, developmental stages, and behavioural contexts.

“Standardising methodologies will avoid confusion and enable meaningful comparisons across species, populations, sexes, developmental stages, and behavioural contexts (Broughton 1963; Ruxton and Schaefer 2011; Kershenbaum et al. 2016).”

• cites Broughton 1963Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Ruxton and Schaefer 2011 sourceNot checked — no full text of the source
• cites Kershenbaum et al. 2016 sourcePartly supported

  The Abstract (page unavailable) proposes a uniform approach to clarify terminology and facilitate comparative studies across taxa, supporting the claim’s general point. The Introduction likewise describes bridging inconsistent terminology across disciplines and taxa. The paper does not specifically say that standardisation will enable comparisons across populations, sexes, developmental stages, and behavioural contexts. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Vocalisations are composed of a fundamental frequency, harmonics, and for some species formants, all of which potentially modulate in frequency and amplitude across time.

“Vocalisations, for example, are composed of a fundamental frequency, harmonics (Vergne et al. 2012), and for some species formants (Reber et al. 2015, 2017), all of which potentially modulate in frequency and amplitude across time (Vergne et al. 2012).”

• cites Vergne et al. 2012 sourceNot checked — no full text of the source
• cites Reber et al. 2015 sourceSupported
• cites Reber et al. 2017 sourceSupported

May combine two claims.

Crocodylians appear most vocal during the mating season and at night.

“Overall, crocodylians appear most vocal during the mating season (Garrick and Lang 1977) and at night (Vliet 1989; Brien et al. 2013; Campbell et al. 2014; Staniewicz et al. 2023).”

• cites Garrick and Lang 1977 sourcePartly supported

  The Discussion (page not provided) says American alligator bellowing peaks at the same time as courtship, supporting the mating-season portion of the claim for that vocalization. It does not establish that crocodylians generally are most vocal then; the Comparison of Signals and Signalling Systems section says vocal signals are used more commonly in American alligators than in the two crocodile species. The nighttime portion is attributed to other citations, not this paper. (LLM, conf=0.85)

  Experimental — accuracy not yet measured
• cites Vliet 1989 sourceNot checked — no full text of the source
• cites Brien et al. 2013Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Formants exist in the bellows produced by the Chinese alligator and likely also the American alligator.

“Such formants exist in the bellows produced by the Chinese alligator (Alligator sinensis, Fauvel 1879) (Reber et al. 2015) and likely also the American alligator (Alligator mississippiensis, Daudin 1801) (Reber et al. 2017).”

• cites Reber et al. 2015 sourceSupported
• cites Reber et al. 2017 sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

Percussion is a means of acoustic signalling involving sounds created by body-body or body‐object striking, such as jaw pops and headslaps.

“A third means of acoustic signalling is percussion, involving sounds created by body–body or body‐object striking, such as jaw pops and headslaps (Vergne et al. 2009; Riede et al. 2011, 2015).”

• cites Vergne et al. 2009 sourceNot checked — no full text of the source
• cites Riede et al. 2011 sourceCould not verify

  The Materials and Methods and Results passages describe juvenile alligator contact calls produced by vocalization, not percussion. Searches for jaw pops, headslaps, striking, and non-vocal acoustic signals found no passage in our copy addressing the claimed form of signalling; page numbers were unavailable. (LLM, conf=0.76)

  Experimental — accuracy not yet measured
• cites Riede et al. 2015 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S2 (checkable).

Understanding acoustic signal measurements is essential for interpreting species-specific communication strategies, ecological adaptations and behavioural functions.

“This is significant as understanding acoustic signal measurements is essential for interpreting species‐specific communication strategies, ecological adaptations and behavioural functions (Alcocer et al. 2022).”

• cites Alcocer et al. 2022 sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Vocalisations such as growls, roars, and bellows are produced by air pressure travelling through the laryngeal vocal folds causing them to vibrate through the trachea, with resonance produced by the vocal tract.

“These include vocalisations such as growls, roars (in crocodiles) and bellows (in alligators), all of which are produced by air pressure travelling through the laryngeal vocal folds causing them to vibrate through the trachea, with resonance produced by the vocal tract (Riede et al. 2011; Reber et al. 2017).”

• cites Riede et al. 2011 sourcePartly supported

  The Introduction and Materials and Methods describe airflow through the alligator larynx causing vocal-fold vibration, and the Discussion mentions alligator bellows. But the study examines juvenile contact calls, not the production of growls, crocodile roars, or bellows; the Discussion says the vocal tract’s contribution to sound properties needs further study, so it does not establish the claimed resonance mechanism. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites Reber et al. 2017 sourcePartly supported

  The Introduction identifies bellowing and roaring as crocodilian vocalisations, and the Discussion supports vocal-tract resonance in alligator bellows. But the Discussion explicitly says it remains unclear whether the vibrating tissue is the vocal folds, so the cited paper does not support that part of the proposed mechanism. The supplied passages have no page numbers. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

Signals measured in air were (and are) not comparable to the same signals measured underwater, due to both differences in sound propagation and differences in crocodylian acoustic signal perception.

“Likewise, signals measured in air were (and are) not comparable to the same signals measured underwater, due to both differences in sound propagation and differences in crocodylian acoustic signal perception (Higgs et al. 2002; Papet et al. 2019).”

• cites Higgs et al. 2002 sourceNot checked — no full text of the source
• cites Papet et al. 2019 sourcePartly supported

  The Introduction says air and water have different sound-propagation properties. But the Methods specify that the ears remained above water, and the Discussion says the study focused on aerial hearing and leaves underwater localization for future research. It therefore does not establish that the same signals measured in air and underwater are incomparable, or that differences in crocodilian perception make them so. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

May combine two claims.

Speight et al. (2025) demonstrate an uneven distribution of studies based on IUCN threat status, gross domestic product per capita, and taxonomic group, with notable biases toward 'Least Concern' species, studies conducted in the United States and a general neglect of reptile groups.

“For example, Speight et al. (2025) demonstrate an uneven distribution of studies based on IUCN threat status, gross domestic product per capita, and taxonomic group, with notable biases toward ‘Least Concern’ species, studies conducted in the United States and a general neglect of reptile groups.”

• cites Speight et al. (2025) sourceSupported

May combine two claims.

In other studies, the acoustic parameters of crocodylian acoustic signals are affected by habitat, anthropogenic disturbance and signalling location (air vs. water).

“In other studies, the acoustic parameters of crocodylian acoustic signals are affected by habitat (Dinets 2011, 2013a, 2013b), anthropogenic disturbance (Boucher et al. 2020) and signalling location (air vs. water) (Jensen et al. 2024) indicating the importance of context.”

• cites Dinets 2011, 2013a, 2013bNot matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Boucher et al. 2020 sourcePartly supported

  The Abstract reports that distress-call parameters of juvenile and hatchling American crocodiles varied among sites in relation to human disturbance. However, the Discussion (Call production; page unavailable) says further research is needed to determine whether those differences truly reflect anthropogenic impact. The citing sentence states the effect more definitively than the source does; the habitat and air-versus-water portions are attributed to other citations. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Research effort to document crocodylian species repertoires may be disproportionately concentrated in regions where species are less threatened, due to more readily available funding.

“we acknowledge that research effort to document crocodylian species repertoires may be disproportionately concentrated in regions where species are less threatened, due to more readily available funding”

• cites Moura and Jetz 2021 sourcePartly supported

  The Main Text (page unavailable) describes geographically uneven species-discovery activity and says that expertise and support for discovery are tied to nations. It does not say that crocodylian research is concentrated where species are less threatened, or that greater funding causes such a pattern. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

The contexts for hissing in crocodylians are highly variable and include aggression, defence and courtship.

“Additionally, the contexts for hissing in crocodylians are highly variable and include aggression, defence and courtship (Garrick and Lang 1977; Garrick et al. 1978; Wang et al. 2007; Dinets 2010).”

• cites Garrick and Lang 1977 sourceSupported
• cites Garrick et al. 1978 sourceNot checked — no full text of the source
• cites Dinets 2010Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

This size-frequency relationship is based on whether vocal fold size (the main determinant of frequency) correlates with overall body size, which may not be the case for all species.

“This size‐frequency relationship is based on whether vocal fold size (the main determinant of frequency) correlates with overall body size, which may not be the case for all species (Reber et al. 2017; Jensen et al. 2024).”

• cites Reber et al. 2017 sourcePartly supported

  The Introduction (page unavailable) says that fundamental frequency reflects the rate of source-tissue vibration and that, in many species, it has no apparent link to body size, possibly because vibrating-tissue size is not tightly constrained by anatomy. This supports the claim that a size–frequency relationship need not hold across species, but the paper does not establish that vocal-fold size is the main determinant of frequency. (LLM, conf=0.81)

  Experimental — accuracy not yet measured
• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The spectral centroid is an important predictor of individuality in the American alligator bellow, and size in the contact call of juveniles from various species.

“The spectral centroid is an important predictor of individuality in the American alligator bellow (Jensen et al. 2024), and size in the contact call of juveniles from various species (Chabert et al. 2015).”

• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Chabert et al. 2015 sourceSupported

May combine two claims.

Differences in acoustic signalling syntax may allow species identification and potentially contain contextual, individual and/or behavioural information.

“Differences in acoustic signalling syntax (i.e., the sequence of signal elements) may allow species identification and potentially contain contextual, individual and/or behavioural information (Garrick et al. 1978; Kershenbaum et al. 2016).”

• cites Garrick et al. 1978 sourceNot checked — no full text of the source
• cites Kershenbaum et al. 2016 sourcePartly supported

  Section VI(3), “How do individual differences in acoustic sequences arise?”, says variation in syntax may reflect aggression and that phrase sequences can distinguish individual birds. Section IV(7) describes different call sequences carrying different meanings, supporting the possibility of contextual or behavioural information. Section VI(4) discusses a possible role for sequence syntax in speciation, but does not establish that syntactic differences allow species identification. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

Sex appears to significantly predict some of the acoustic parameters of different call types, and dominant frequency (along with all formant-related parameters) in American alligator bellows is higher in females than in males, with this trend consistent across studies.

“Sex appears to significantly predict some of the acoustic parameters of different call types.”

• Also stated in: § Influence of Species, Sex, Size and Life Stage · plain

  “Dominant frequency (along with all formant‐related parameters) in American alligator bellows is also higher in females than that of males, with this trend consistent across studies (Reber et al. 2017; Jensen et al. 2024).”

• cites Reber et al. 2017 sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured
• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Recent breakthroughs have demonstrated that less data can be sufficient for machine learning call detection and identification, depending on research goals.

“but recent breakthroughs have demonstrated that less data can be sufficient, depending on research goals (Knight et al. 2020; Eichinski et al. 2022).”

• cites Knight et al. 2020 sourceNot checked — no full text of the source
• cites Eichinski et al. 2022 sourceSupported

May combine two claims.

Formants are produced from the resonance of the vocal tract and therefore scale with body size, and have been shown to contain individual identity, predict sex in American alligator bellows, and likely contain information pertaining to body size and fitness in this species.

“Formants are produced from the resonance of the vocal tract and therefore scale with body size (Reber et al. 2017).”

• Also stated in: § Acoustic Parameter Measurements and Associated Behaviours · hedged

  “They have been shown to contain individual identity, and to predict sex in American alligator bellows and likely contain information pertaining to body size and fitness in this species (Jensen et al. 2024).”

• cites Reber et al. 2017 sourceSupported
• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Formant frequency of an acoustic signal is produced from resonant frequencies of the vocal tract, which is constrained and scales according to body size.

“Formant frequency of an acoustic signal, in contrast, is produced from resonant frequencies of the vocal tract, which is constrained and scales according to body size.”

• cites Fitch and Hauser 2002Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Hodges‐Simeon et al. 2014 sourcePartly supported

  The Introduction says vocal-tract dimensions determine formants, supporting the claim about their acoustic origin. It also says evidence that formant structure scales with overall body size is inconclusive. The Discussion reports that strength, rather than height or adiposity, predicts formant position when those measures are considered together. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

Manually processing the vast amount of data gathered through passive acoustic monitoring can require significant time investment, often not feasible for most researchers.

“Manually processing the vast amount of data gathered through passive acoustic monitoring can require significant time investment, often not feasible for most researchers (Stowell 2022).”

• cites Stowell 2022 sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

Machine learning techniques are revolutionising acoustic data processing through the development of automatic detection, measurement, and species-specific call recognisers.

“However, machine learning techniques to process acoustic data are revolutionising such studies, through the development of techniques including automatic detection, measurement, and the application of species‐specific call recognisers (Bianco et al. 2019; Teixeira et al. 2019; Eichinski et al. 2022; Stowell 2022).”

• cites Bianco et al. 2019 sourceSupported
• cites Teixeira et al. 2019 sourcePartly supported

  Section 3 (page unavailable) describes algorithms that automatically detect vocalizations and gives species-specific examples of call recognizers. It does not establish that machine learning is revolutionising acoustic-data processing or describe automatic measurement; it also cautions that recognizer reliability is mixed. The conclusion (section 4, page unavailable) says sound-data processing remains a limitation. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites Eichinski et al. 2022 sourcePartly supported

  The Abstract describes a neural-network recognizer that automatically detects calls from seven bird species, and Related Research describes advances in automated acoustic analysis. These passages support detection and species-specific call recognition, but they do not establish the claim about automatic measurement; the paper also does not itself characterize these techniques as revolutionising acoustic studies. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

Machine learning for call detection and identification has traditionally required a significant amount of pre-processed data.

“Machine learning for call detection and identification has traditionally required a significant amount of pre‐processed data”

• cites Knight et al. 2020 sourceNot checked — no full text of the source
• cites Eichinski et al. 2022 sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

It is unknown whether crocodylians produce hissing via the mouth or the nose.

“Hissing in particular is intriguing, as it is unknown whether animals produce this signal via the mouth (Garrick and Lang 1977) or the nose (Wang et al. 2007).”

• cites Garrick and Lang 1977 sourceCould not verify

  The Comparison of Signals and Signalling Systems section says all three species hiss, but does not say whether hissing is produced through the mouth or nose, or that its route is unknown. Searches for hissing with an open mouth and for nasal exhalation found no passage connecting either route to hissing; the mouth-open display described there accompanies a growl. (LLM, conf=0.76)

  Experimental — accuracy not yet measured
• cites Wang et al. 2007 sourceNot checked — no full text of the source

May combine two claims.

The distress call was represented most broadly across crocodylian species (84.6%, n=11), with only the Chinese alligator and African dwarf crocodile missing measurements for this call type.

“The distress call was represented most broadly across crocodylian species (84.6%, n = 11) with only the Chinese alligator and African dwarf crocodile missing measurements for this call type (Figure 3a).”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Six of the species with published acoustic parameters are Least Concern, three are Vulnerable, and four are Critically Endangered.

“Six of these are Least Concern, three are Vulnerable and four are listed as Critically Endangered by the IUCN (IUCN 2024) (Figure A1).”

• cites IUCN 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

In sub-adults and adults, distress calls have very little frequency modulation, lower frequency, and longer duration.

“Sub‐adults & adults: very little frequency modulation, lower frequency, longer duration 4 , 8”

• cites [4]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [8]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Bubbles have a bandwidth of 1068 ± 562 Hz.

“Bandwidth (Hz)W: 1068 ± 562 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Contact calls are short, often repeated chirp-like sounds.

“Short, often repeated chirp‐like sound 7 , 15 , 36”

• cites [7]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [15]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [36]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Bubbles have a duration of 2.06 ± 1.54 s.

“Duration (s)W: 2.06 ± 1.54 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Coughs have a dominant frequency of 300 Hz.

“Dominant frequency (Hz):300 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

77% (n=17) of included publications were published after 2007.

“A total of 22 publications were included for analysis in our systematic literature review, with the first study published in 1973 (Campbell 1973) and 77% (n = 17) published after 2007.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Drums have a duration of 0.29-0.38 s.

“Duration (s): 0.29–0.38 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims. The quote only partly states this claim.

Coughs are noisy, broadband sounds of short duration with energy concentrated in lower frequencies.

“Noisy, broadband sound of short duration with energy concentrated in lower frequencies 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Coughs are produced by adult male and female crocodilians.

“Adult male & female 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The 'Moo' reported by Staniewicz et al. (2023) and Wang et al. (2007) appeared to exhibit distinct spectrographic characteristics, suggesting they may represent acoustically different call types.

“Upon examination of the spectrograms, the signal, referred to as a ‘Moo’ by both Staniewicz et al. (2023) and Wang et al. (2007) appeared to exhibit distinct spectrographic characteristics, suggesting it may represent acoustically different call types.”

• cites Staniewicz et al. (2023) sourceNot checked — no full text of the source
• cites Wang et al. (2007) sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

The first study was published in 1973.

“A total of 22 publications were included for analysis in our systematic literature review, with the first study published in 1973 (Campbell 1973) and 77% (n = 17) published after 2007.”

• cites Campbell 1973Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Coughs are often produced in a sequence of three.

“Often produced in a sequence of three. 17 , 29”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The number of individuals sampled in each study ranged from 1 to 31 crocodiles of known identity and included groups of 20 to 120 individuals.

“The number of individuals sampled in each study ranged from 1 to 31 crocodiles of known identity and included groups of crocodiles ranging between 20 and 120 individuals, as well as 67 instances where the exact number of individuals was unknown.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Drums are produced by adult crocodilians of unknown sex (paired male and female observed).

“Adult, sex unknown (paired male & female observed) 29 , 30”

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Drums are low frequency hollow thump sounds that are repeated depending on whether the signal is a single, double or triple drum.

“Low frequency hollow thump sound that is repeated depending on whether the signal is a single, double or triple drum”

May combine two claims.

Distress calls are graded upwards in intensity from the contact call, being louder, repeated more frequently, and having higher amplitude, energy and volume.

“Graded upwards in intensity from the contact call, so is louder, repeated more frequently and has higher amplitude, energy and volume 37”

• cites [37]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The quote only partly states this claim.

Drums have a dominant frequency of 30-34 Hz.

“Dominant frequency (Hz): 30–34 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

Coughs lack harmonics.

“Harmonics absent 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Coughs are deep, short, bark-like sounds with an abrupt ending.

“Deep, short, bark‐like, with abrupt ending 17 , 29”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

In hatchlings and juveniles, distress calls have complex frequency modulation, higher frequency, and shorter duration.

“Hatchlings & juveniles: complex frequency modulation, higher frequency, shorter duration 4 , 8 , 25 , 35 , 36 , 37”

• cites [4]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [8]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [25]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Species with published acoustic parameters were globally distributed, with seven from the Americas, two each from Africa and Southeast Asia, and one each from China and the Indian subcontinent.

“Those species with acoustic parameters published were also globally distributed, with seven from the Americas, two each from Africa and Southeast Asia, and one each from China and the Indian subcontinent.”

May combine two claims.

Distress call frequency varies depending on the position of the palatal valve (moan-like when closed, screech-like when open) and the life stage of the individual.

“Varies in frequency depending on the position of the palatal valve (moan‐like = closed, screech‐like = open) 25 and the life stage of the individual 4”

• cites [25]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [4]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Bubbles are a low-energy acoustic signal with energy concentrated in the lower frequencies and bandwidth decreasing over time.

“Low energy acoustic signal with energy concentrated in the lower frequencies and bandwidth decreasing over time”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Coughs have a duration of 0.20-0.31 s.

“Duration (s): 0.20–0.31 17 , 29”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Drums are mostly produced singularly but may occur in sequences of up to five or with other signal types.

“Mostly produced singularly but may occur in sequences of up to five or with other signal types 29 , 30”

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S4 (based).

There is no peer-reviewed publication that consolidates and standardises acoustic signal measurements collected from crocodylians in captive and wild settings.

“To our knowledge, there is no peer‐reviewed publication that consolidates and standardises acoustic signal measurements collected from crocodylians in captive and wild settings.”

May combine two claims.

Most call measurements were recorded in response to a threat (49.7%, n=309), followed by calls made in an unknown context (14.8%, n=92) and then those emitted during courtship (11.1%, n=69).

“Most call measurements were recorded in response to a threat (49.7%, n = 309), followed by calls made in an unknown context (14.8%, n = 92) and then those emitted during courtship (11.1%, n = 69).”

May combine two claims.

All species produced distress calls with similar durations and fundamental frequency (when measured across the entire call), apart from gharials, whose calls were longer in duration and higher in fundamental frequency than all other species.

“All species produced distress calls with similar durations (Figure 4f) and fundamental frequency (when measured across the entire call), apart from gharials, whose calls were longer in duration and higher in fundamental frequency than all other species.”

May combine two claims.

The dataset contained 623 total observations and 54 distinct acoustic parameters, with most parameters (55.0%, n=343) related to FED.

“For the 623 total observations collated (Supporting Information Table S4) we were able to categorise 54 distinct acoustic parameters, most of which (55.0%, n = 343) were related to FED.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Moos have a duration of 1.03 ± 0.27 s.

“Duration (s): 1.03 ± 0.27 41”

• cites [41]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Most studies included in this review targeted calls made in a threat context (50.8%), whereby calls were induced primarily by capture, and these distress calls were produced predominantly by hatchling or juvenile individuals.

“Most studies included in this review targeted calls made in a threat context (50.8%), whereby calls were induced primarily by capture.”

• Also stated in: § Focuses in the Published Literature and Knowledge Gaps · plain

  “Furthermore, these distress calls were produced predominantly by hatchling or juvenile individuals.”

May combine two claims.

Most parameters (92.2%, n=573) were measured from individuals of unknown sex, with 4.3% (n=27) and 3.5% (n=22) measured from known males and females, respectively.

“Most parameters (92.2%, n = 573) were measured from individuals of unknown sex, with 4.3% (n = 27) and 3.5% (n = 22) measured from known males and females, respectively”

Probably not a substantial claim: may not pass S3 (load-bearing).

Pops are sudden, hollow sounding percussive signals.

“Sudden, hollow sounding percussive signal 1”

• cites [1]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

All distress call measurements reported in the literature were measured in air and produced by individuals of unknown sex.

“All distress call measurements reported in the literature were measured in air and produced by individuals of unknown sex.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Gusts decrease in both frequency and energy throughout.

“Decreases in both frequency and energy throughout”

May combine two claims.

Adult male American alligators produced calls longer in duration than conspecific female adults, and for American alligators, the duration of bellow cycles was longer in males than in females, and formant frequency was lower in males than in females.

“adult male American alligators produced calls longer in duration than conspecific female adults.”

• Also stated in: § Parameter Comparison Across Species, Sex and Life Stage · plain

  “For American alligators, the duration of bellow cycles was longer in males than in females, and formant frequency was lower in males than in females”

May combine two claims.

There was a low degree of consistency in the use of acoustic parameters when measuring crocodylian calls, with the majority (67.9%, n=36) representing <1% each within the dataset.

“There was a low degree of consistency in the use of acoustic parameters when measuring crocodylian calls, with the majority (67.9%, n = 36) representing < 1% each within the dataset.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Gusts have a duration of 1.88-2.34 s.

“Duration (s): 1.88–2.34 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The quote only partly states this claim.

Moos have a dominant frequency of 273 ± 57.01 Hz.

“Dominant frequency (Hz): 273 ± 57.01 41”

• cites [41]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The rumble acoustic signal was measured in both air and underwater across two species; however the only parameter available for comparison across the same media was dominant frequency measured underwater, which was much higher when produced by false gharials than by African dwarf crocodiles.

“The rumble acoustic signal was measured in both air and underwater across two species; however the only parameter available for comparison across the same media was dominant frequency measured underwater, which we found was much higher when produced by false gharials than by African dwarf crocodiles.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Moo-1 sounds have harmonics present.

“Harmonics present 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Gusts have a dominant frequency of 179-259 Hz.

“Dominant frequency (Hz): 179–259 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Moans are short sigh-like sounds that decrease in frequency.

“A short sigh‐like sound that decreases in frequency”

May combine two claims.

Adult Chinese alligator (unknown sex) hisses were much longer in duration than those of adult (female) Yacare caiman, or adult American alligator (unknown sex) adults.

“Adult Chinese alligator (unknown sex) hisses were much longer in duration than those of adult (female) Yacare caiman ( Caiman yacare , Daudin 1801), or adult American alligator (unknown sex) adults.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Growls are deep, guttural, rumbling noises of any volume.

“Deep, guttural, rumbling noise of any volume 17 , 40”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [40]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Growls have a dominant frequency of 100 Hz.

“Dominant frequency (Hz): 100 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Growls are frequency modulated with energy concentrated in lower frequencies.

“Frequency modulated with energy concentrated in lower frequencies 7 , 17”

• cites [7]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Parameters measuring time window, time energy distribution, and other measurements comprised 16.4% (n=102), 15.1% (n=94), and 13.5% (n=84) respectively.

“Parameters measuring time window (TW), time energy distribution (TED), and other measurements (OT) comprised just 16.4% (n = 102), 15.1% (n = 94) and 13.5% (n = 84), respectively”

May combine two claims.

More than half of the dataset (64.2%, n=400) represents measurements made by calls that were induced, with the majority of these made by capture of an individual (49.0%, n=305), all of which were emitted as distress calls.

“More than half of the dataset (64.2%, n = 400) represents measurements made by calls that were induced, with the majority of these made by capture of an individual (49.0%, n = 305), all of which were emitted as distress calls”

May combine two claims.

Most publications measured distress or contact calls in young and focused on American alligators and/or Nile crocodiles.

“Most publications measured distress or contact calls in young and focused on American alligators and/or Nile crocodiles.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Gusts are low frequency wind-like sounds.

“Low frequency wind‐like sound”

Probably not a substantial claim: may not pass S3 (load-bearing).

Gusts usually occur with rumbles or drums.

“Usually occurs with rumbles or drums”

Probably not a substantial claim: may not pass S3 (load-bearing).

Grunts have harmonics present.

“Harmonics present Formants unknown F0 (Hz): 50 17”

May combine two claims.

Duration was measured in five species for the contact call and showed that the American crocodile had the longest duration and the black caiman the shortest.

“Duration was measured in five species for the contact call and showed that the American crocodile ( Crocodylus acutus , Cuvier 1807) had the longest duration and the black caiman the shortest”

Probably not a substantial claim: may not pass S3 (load-bearing).

Moans have a bandwidth of 306 ± 92 Hz.

“Bandwidth (Hz)W: 306 ± 92 29”

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Headslaps may be repeated by the same individual and may be produced in a chorus of multiple individuals.

“May be repeated by the same individual 16 , 17 , 18 , 40 May be produced in a ‘chorus’ of multiple individuals 16 , 17 , 18 , 40”

• cites [16]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [18]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Life stages were represented by juveniles 31.0% (n=193), adults 27.7% (n=172), hatchlings 20.6% (n=128), sub-adults 14.0% (n=87), and pre-hatching 1.6% (n=10).

“Life stages were more evenly represented, with juveniles accounting for 31.0% (n = 193), adults 27.7% (n = 172), hatchlings 20.6% (n = 128), sub‐adults 14.0% (n = 87) and pre‐hatching 1.6% (n = 10)”

Probably not a substantial claim: may not pass S3 (load-bearing).

Moo-1 sounds have a duration of 2.91-3.14 s.

“Duration (s): 2.91–3.14 30”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Hisses are noisy, broad bandwidth sounds lacking melodic structure.

“Noisy, broad bandwidth sound lacking melodic structure 28”

• cites [28]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Moo-1 sounds are groan-like sounds that increase in volume and frequency toward the centre of the call and decrease in frequency at the end of the call.

“A groan‐like sound that increases in volume and frequency toward the centre of the call, and decreases in frequency at the end of the call”

Probably not a substantial claim: may not pass S3 (load-bearing).

Grunts are deep, short, burp-like sounds.

“Deep, short, burp‐like 17 , 33”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [33]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Duration was the most commonly measured parameter (9.3%, n=58), followed by dominant frequency (7.7%, n=48) and fundamental frequency at the end of the measured signal (F0 [END]) (5.9%, n=37).

“Duration (s) was the most commonly measured parameter (9.3%, n = 58), followed by dominant frequency (Hz) (7.7%, n = 48) and fundamental frequency at the end of the measured signal (F0 [END] (Hz)) (5.9%, n = 37).”

May combine two claims.

Distress calls produced by juvenile American alligators had the highest dominant frequency but one of the lowest centre frequency measurements when compared to the five other species measured.

“Notably, distress calls produced by juvenile American alligators had the highest dominant frequency but one of the lowest centre frequency measurements when compared to the five other species measured”

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Headslaps have a duration of 0.16 s.

“Duration (s): 0.16 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Grunts have an F0 of 50 Hz.

“F0 (Hz): 50 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Drum calls could only be compared between species underwater, with the dominant frequency of African dwarf crocodile signals found to be much higher than that of false gharials.

“Drum calls could only be compared between species underwater, with the dominant frequency of African dwarf crocodile signals found to be much higher than that of false gharials.”

May combine two claims.

Headslaps are high energy rapid sounds with a broad bandwidth spike.

“High energy rapid sound, with a broad bandwidth spike”

Probably not a substantial claim: may not pass S3 (load-bearing).

Moos are often produced before a headslap.

“Often produced before a headslap 41”

• cites [41]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Moans have harmonics present.

“Harmonics present 29”

• cites [29]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Hisses are long, soft, 'SSSSSS' sounds.

“Long, soft, ‘SSSSSS’ sound 16 , 17 , 18 , 41”

• cites [16]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [18]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

It is unclear whether the stronger response of Nile crocodile mothers to smaller offspring depended on formant frequencies, because formants were not measured in that study.

“Unfortunately, it is unclear whether this response was dependent on formant frequencies, since these were not measured.”

May combine two claims.

Published, peer-reviewed studies to date focus primarily on only a few species, with most extant crocodylians lacking any published acoustic signal data.

“Published, peer‐reviewed studies to date focus primarily on only a few species, with most extant crocodylians lacking any published acoustic signal data.”

May combine two claims.

No studies have specifically measured and compared crocodylian acoustic features over longer timeframes, so very little is known about how signals develop or vary across an individual's lifespan.

“no studies have specifically measured and compared these features over longer timeframes; thus very little is known about how signals develop or vary across an individual's lifespan.”

May combine two claims.

This review found a strong research focus on frequency-based parameters, comprising over half of the dataset, while time-window and time-energy parameters were reported far less frequently in the published literature.

“This is particularly noteworthy as our review highlights a strong research focus on frequency‐based parameters (comprising over half of the dataset), while time‐window and time‐energy parameters were reported far less frequently in the published literature.”

Classified as probably not a substantial claim.

The authors were able to construct a standardised ethogram of each crocodylian acoustic signal type, including representative spectrograms.

“we were able to construct a standardised ethogram of each acoustic signal type, including representative spectrograms.”

May combine two claims.

Across 13 crocodylian species, over 600 measurements of acoustic parameters were able to be analysed from the literature, and the analysis consolidated the existing information into a standardised and detailed ethogram.

“Across 13 crocodylian species, over 600 measurements of acoustic parameters were able to be analysed from the literature.”

• Also stated in: § Acoustic Parameter Measurements and Associated Behaviours · plain

  “was able to consolidate the existing information in such a way that allowed the creation of a standardised and detailed ethogram that we hope will be used in future studies.”

Classified as probably not a substantial claim.

It is unknown whether formants exist in calls produced by crocodylian genera other than the alligators studied.

“It is unknown whether formants exist in calls produced by other crocodylian genera however, highlighting a significant gap in our understanding of crocodylian acoustic communication and its evolution”

May combine two claims.

Where comparisons of acoustic signals were possible, differences in measured parameters of signals could often be explained by sex, life stage or size of the calling individual, and species-specific differences were found in virtually every call type where comparisons of parameter mean values were possible.

“Where comparisons of acoustic signals were possible, we found differences in measured parameters of signals could often be explained by sex, life stage or size of the calling individual.”

• Also stated in: § Influence of Species, Sex, Size and Life Stage · plain

  “We found species‐specific differences in virtually every call type where comparisons of parameter mean values were possible (bellow, contact call, distress call, drum, grunt, hiss, rumble).”

Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based).

Coughs are emitted in a courtship context.

“Courtship 17”

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Distress calls function to solicit protection and signal distress and threat response.

“Solicit protection, distress, threat response 3 , 4 , 7 , 8 , 15 , 16 , 17 , 18 , 25 , 35 , 36 , 37”

• cites [3]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [4]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [7]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Classified as probably not a substantial claim. May combine two claims.

Roars (Crocodylidae) and bellows (Alligatoridae) are functionally equivalent signals and were combined under the term 'bellows'.

“Common terms for specific signal types were chosen to represent the same functionally equivalent signal, e.g., ‘roars’ (Crocodylidae) and ‘bellows’ (Alligatoridae), which were combined under the term ‘bellows’ (Grigg and Kirshner 2015; Jensen et al. 2024).”

• cites Grigg and Kirshner 2015Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Jensen et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Recent advances in bioacoustic technology have enabled identification of low frequency underwater signals including moos, rumbles, drums, gusts and moans.

“Additionally, recent advances in bioacoustic technology have enabled identification of low frequency underwater signals including moos, rumbles, drums, gusts and moans (Staniewicz et al. 2022, 2023).”

• cites Staniewicz et al. 2022Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Staniewicz et al. 2023 sourceNot checked — no full text of the source

May combine two claims.

Contact calls originate from the vocal tract, subglottal pressure, and vocal fold adduction.

“Vocal tract, subglottal pressure, and vocal fold adduction 24”

• cites [24]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Respiratory signals differ from vocalisations in that they are produced by forceful exhalation without tracheal vibration or resonance.

“Respiratory signals differ from vocalisations in that they are produced by forceful exhalation without tracheal vibration or resonance.”

Probably not a substantial claim: may not pass S3 (load-bearing). The quote only partly states this claim.

Drums are emitted in a courtship context.

“Not specified 30 , Courtships”

• cites [30]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The screening approach ensured that all included data was reliable, repeatable, and suitable for synthesis.

“This approach ensured that all included data was reliable, repeatable, and suitable for synthesis.”

May combine two claims.

These modulations can make vocalisations appear indistinct on a spectrogram, making crocodylian vocalisations complex to measure.

“These modulations can make vocalisations appear indistinct on a spectrogram, thus making crocodylian vocalisations complex to measure.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The dataset was complete and free of missing values.

“No data imputation, statistical corrections or transformations were applied during analysis, as the dataset was complete and free of missing values.”

May combine two claims.

Contact calls function in social cohesion, alerting to environmental features (i.e., food), individual localisation, and interest.

“Social cohesion, alert to environmental features (i.e., food), individual localisation, interest 7 , 18 , 35 , 36 , 37 , 38”

• cites [7]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [18]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [35]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The lack of description of underwater acoustic signals represents a significant gap in the literature, and limits our understanding of crocodylian communication systems and their underwater social behaviours.

“The lack of description of underwater acoustic signals thus represents a significant gap in the literature, and limits our understanding of crocodylian communication systems and their underwater social behaviours.”

May combine two claims.

Headslaps originate from body-body (upper-lower jaw) and body-object (underside of jaw and head-water surface) contact.

“Body—body (upper—lower jaw) & body—object (underside of jaw & head—water surface) 16 , 17 , 18 , 40”

• cites [16]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [17]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [18]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.