The function of crocodile hatchling (Crocodylus acutus) distress calls


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The function of crocodile hatchling (Crocodylus acutus) distress calls
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La función de las llamadas de socorro de crías de cocodrilo (Crocodylus acutus)
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Ramireddy, Dhiraj
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This study attempts to describe communication and behavior among Crocodylus acutus hatchlings. By understanding when and why vocalizations occur, new insight can be found regarding extant ancestors of crocodilians including dinosaurs. In Cuajiniquil, Costa Rica, I observed two Crocodylus acutus nests and captured five crocodile hatchlings. I observed the captured hatchling and its siblings recording vocalizations and movement patterns. After catching a random hatchling, it vocalized distress calls, and in response, the siblings would vocalize and approach the captive. These results support the hypothesis that a distress call of a hatchling seeks help from sibling crocodiles. An acoustical analysis displayed a similar spectrogram for the distress call of the captive and the response of sibling hatchlings. This echoing of the captive’s distress call could possibly alert or call for the mother crocodile. ( , )
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Este estudio intenta describir la comunicación y el comportamiento entre las crías de Crocodylus acutus. Al comprender cuándo y por qué se producen las vocalizaciones, se puede conocer más sobre los antepasados de los cocodrilos, incluidos los dinosaurios. En Cuajiniquil, Guanacaste Costa Rica, observé dos nidos de Crocodylus acutus, con cinco crías de cocodrilo. Observé cada cría capturada y sus hermanos grabando sus vocalizaciones y patrones de movimiento. Después de atrapar cada cría al azar, ésta vocalizó las llamadas de socorro, y en respuesta las crías hermanas vocalizaron y se acercaron a la cría cautiva. Estos resultados apoyan la idea de que una llamada de emergencia de una cría busca la ayuda de los demás cocodrilos emparentados. El análisis acústico mostró un espectrograma similar en la llamada de socorro del cautivo y las respuestas acústicas de las crías hermanas. La llamada de socorro de la cría cautiva también podría alertar y llamar a la madre cocodrilo.
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Student affiliation : Department of Ecology and Evolutionary Biology; University of California Los Angeles
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The function of crocodile hatchling ( Crocodylus acu tus ) distress calls Dhiraj Ramireddy Department of Ecology and Evolutionary Biolog y University of California Los Angeles EAP Tropical Biology and Conservation Program, Spring 2019 7 June 2019 ABSTRACT This study attempts to describe communication and behavior among Crocodylus acutus hatchlings. By understanding when and why vocalizations occur, new insight can be found regarding extant ancestors of crocodilians including dinosaurs. In Cuajiniquil, Costa Rica, I observed two Crocodylus acutus nests and captured five crocodile hatchlings. I observed the captured hatchling and its siblings record ing vocalizations and movement patterns. After catching a random hatchlin g , it vocalized distress calls, and in response, the siblings would vocalize and approach the captive. These re sults support the hypothesis that a distress call of a hatchling seeks help from sibling crocodiles . An acoustical analysis displayed a similar sp ectrogram for the distress call of the captive and the response of sibling hatchlings. This echoing of the captive's distress call could possibly alert or call for the mother crocodile. La funci—n de las llamadas de socorro de cr’as de cocodrilo ( Crocodylus acutus ) RESUMEN Este estudio intenta describir la comunicaci—n y el comportamiento entre las cr’as de Crocodylus acutus . Al comprender cu‡ndo y por quŽ se producen las vocalizaciones, se puede conocer m‡s sobre los antepasados de los cocodrilos , incluidos los dinosaurios. En Cuajiniquil, Guanacaste Costa Rica, observŽ dos nidos de Crocodylus acutus , con cinco cr’as de cocodrilo. ObservŽ cada cr’a capturada y sus hermanos grabando sus vocalizaciones y patrones de movimiento. DespuŽs de atrapar ca da cr’a al azar, Žsta vocaliz— las llamadas de socorro, y en respuesta las cr’as hermanas vocalizaron y se acercaron a la cr’a cautiva. Estos resultados apoyan la idea de que una llamada de emergencia de una cr’a busca la ayuda de los dem‡s cocodrilos empa rentados. El an‡lisis acœstico mostr— un espectrograma similar en la llamada de socorro del cautivo y las respuestas acœsticas de las cr’as hermanas. La llamada de socorro de la cr’a cautiva tambiŽn podr’a alertar y llamar a la madre cocodrilo. I NTRODUCTIO N Crocodilians and birds are the last remaining extant descendants of the Phylum Archosauria (Appendix 1). Despite recent advances in understanding the phylogeny and ecology of ancient dinosaurs, obtaining information regarding their behavior remains a challenge. By studying the extant relatives one can acquire behavioral information. In Costa Rica, Crocodylu s acutu s, the A merican crocodile is also known locally as lagarto or cocodrilo . Male adults range in size from 2.5 to 7 meters. Female adults can grow up

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C rocodile hatchling distress call functions Ramireddy 2 ! to 4 m eters . Hatchling crocodiles are roughly 25 to 30 cm, brown in color , black speckle d , whit e or yellow white ventral unmarked, iris greenish in life (Savage 2002). On 11 May 2019, around 10 pm, Gilbert h Ampie , a local parataxonomist, and his son were strolling along the partially dried up Rio Murcielago in Cuajiniquil, Costa Rica. They heard a squeal , approached the noise, and discovered a " mont—n " ( or "mountain") of hatchling crocodiles along the bank of a small pool. As they were exploring the area, the hatchlings squealed and rushed into the water. They found a crocodile nest that included two eggs roughly 16 cm in circumference and 7.25 cm in height as well as a hatchling crocodile , 25 cm in length. As he picked up the hatchling, he noticed that the other siblings began to vocalize and move towards him and the captive hatchling. After Gilbert h shared his encounter with me, I asked the question : Why do hatchling crocodiles vocalize? To better understand the hatchlings response to a captive sibling, one must understand the mechanisms behind nesting behaviors between hatchlings and the mother. The Crocodylus acutus species has a breeding season from March to May. On ce impregnated, the female digs a hole in sand or soil to form a nest for approximately twenty to sixty eggs then proceeds to cover it with soil and vegetation. The eggs are calcareous, elliptical, about 6.5 cm x 4 cm and weigh about 56 g (Savage 2002 ) . The nest size can range from 40 to 70 cm deep and 50 to 60 cm in diameter. The female tend s to the nest as the eggs take about 75 to 90 days until the cries of the hatchlings trigger her to dig up the eggs with her claws and nose. She will then pick them u p one by one with her mouth and carry them to the nearby water source. M aternal instin cts are strong in all species of crocodilians . F emales guard the nest, help the hatchling s reach the water, and provide protection from predators as the hatchlings grow r apidly in the weeks following hatching. T he eggs and hatchlings are eaten by a variety of small carnivorous mammals and birds (Savage 2002). While the hatchlings are in the mother's care, she frequently excavates a subterranean cave in the banks of waterwa ys; these can be entered only from underwater, are mostly above water level and are used as refuges by the mother and her offspring (Savage 2002). Sound signaling is an efficient means of communication, propagating quickly over long distances even in obstr ucted or dark environments without leaving trails (Bradbury & Vehrencamp, 1998). Crocodiles use olfaction in social interactions but not for hunting prey. Crocodiles have acute hearing ranging from low frequencies (100 Hz) to medium frequencies (6000 Hz) ( Savage 2002). Adults, juveniles, and hatchlings all vocalize but for various reasons. In the case of Gilbert h 's findings, it is the hatchling crocodiles that vocalized in response to the captured sibling. Juvenile crocodilians emit a variety of communication calls that are categorize d into four groups: " hatching calls, " " contact calls, " " distress calls, " and " threat calls " (Vergne 2009) . " Hatching calls " are described as vocalizations with the purpose of al erting the mother that they are ready to hatch as well as synchronizing the time of hatching among st siblings. " Contact calls " are defined as calls that occur to maintain cohesion among the group after hatching. " Distress calls " are the calls whose descrip tion match with the context of G ilbert h 's discovery : vocaliz ation by the hatchling in the presence of a predator or when being seized. D istress calls are separated into two different calls : the ÔÔscreech , '' a loud and high pitched vocalization, and the ÔÔmoan , '' a softer and low pitched distress call (Herzog & Burghardt 1977) . The acoustic structure of distress calls is a complex sound with multiple harmonics showing a down sweeping frequency modulation over the duration of the call (Britton, 2001). It i s believed that the primary

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C rocodile hatchling distress call functions Ramireddy 3 ! function of distress calls is to solicit the protection of an adult (Britton, 2001; Gorzula, 1978; Romero, 1983; A.L. Vergne, T. Aubin, P. Taylor & N. Mathevon, unpublished data). Based on this information regarding the nesting behavior and contexts for vocalization, I was able to hypothesize a few possibilities to why crocodile hatchling s vocalize as depicted in Table 1. Table 1 : Possible hypotheses about the function of hatchling vocalizations and the associated expected obser vation Hypothesis Prediction Alert Siblings Siblings show alertness (raised head) Warn Siblings Siblings flee away from captive Request Help from Siblings Siblings respond and move toward captive Request Help from Mother Mother responds or appears Request Help from another predator Another predator responds or appears Group calls to each other to stay w/ each other Group forms among siblings MATERIALS AND METHODS Capture Methods To recreate the situation Gilbert h observed, we captured hatchling crocodiles and recorded the vocalizations and movements of the captured and sibling hatchlings. Frank Joyce, Gilbert h and I visit ed the site and prepare d a noose stick by tying cord to a long dead branch. One person began r ecording video with a TG 5 camera, one recording sound with a Rode NTG2 microphone a ttached to a Tascam DR 40 Recorder at 44 Hz , and finally one capturing the hatchling. We captured the hatchling by moving with stealth and slipping the noose over the head of the hatchling. Once we removed the noose, we recorded the vocalizations and movements of the captured and sibling hatchlings. We held the hatchling in our hands or in a bucket for about ten minutes and ten meters from the resident pool water. After brin ging the captured hatchling to the shore line, we held it for about three minutes before releasing. We continued to record both audio and video as we observed the original positions of the siblings, mother, and other organism s and record any changes in sta te of being or movements. We would continue to record three minutes after releasing the hatchling. We repeated this method with different hatchlings at two different nests and at various times of the day for a total of five captures. Observation Methods I observed the hatchling crocodiles behind a blind, as to not be seen by them . I set up a blind with trash bags tied by cord to branches of a dense brush. I set up a TG 5 Camera on a tripod and the Rode NTG2 microphone attached to a Tascam DR 40 Recorder nea r the resident pool shoreline. This helped capture evidence of the hatchlings' natural movements and vocalizations. With this information I was able to compare calls made in natural circumstances to those during a capture. With a set of binoculars and a no tebook, I sat quietly behind the blind for hours recording movements, vocalizations, and abnormal behavior with a timestamp. When I was done observing, I pack ed up all supplies and le ft area better than when I found it.

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C rocodile hatchling distress call functions Ramireddy 4 ! RESULTS We captured five hatchlings over one week (Table 2) . Three were caught at night and two during the day. In addition to the captures, I observed both resident pools for a total of 20 hours. All five captives vocalized a distress call when released, and only three vocalized when caught. There were sibling responses in each case. Each case can be broken into three phases: pre capture, capture, release. Table 2 : Summary of behaviors observed during each capture. (+) means observed ( ) did not observe. The pre capture phase represents the period before a capture wa s made. During this time, a potential predator, Gilberth, approache d the pool with a noose stick. Usually , the hatchlings w e re found basking along the bank during the day and floating in the resident pool during both day and night. D uring all five occurrences, the hatchlings fled by turning around and dipping underwater to swim away towards the refuge of the fallen branches . Thre e of the five times the hatchlings vocalized before fleeing (Figure 1). Figure 1 : Flowchart showing actual and possible behavioral paths of the hatchling crocodiles during the pre capture phase. Individual letters refer to individual captures. The capture phase begins once a hatchling is captured and ends when the hatchling is brought back to the shoreline. During the capture phase, the behavior flowchart of the target hatchling was separated from the siblings to better explain what occurred (Fi gure 2). Each target hatchling from the first three captures (A, B, C) vocalized when captured, but neither of two from the last captures (D, E) vocalized. For the instances A, B, C, it did eventually stop vocalizing . Siblings had four possible reactions to a fellow sibling being captured: move towards or away and vocalize or no t vocaliz e . However, it is important to note that the category of moving towards does not mean that all siblings moved towards the call , just at least o ne . For the captures , most or all the hatchlings were hidden , seeking refuge in the den , which means not all possible

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C rocodile hatchling distress call functions Ramireddy 5 ! movements were observ abl e . W hen the captured hatchling was being brought to shore away from the den, four of the five captures ( A, C, D, E ) resulted in at least one sibling crocodile moving in the direction of the captive . During all five occurrences, there were siblings who responded with vocalizations (Figure 2) . Figure 2 : Flowchart showing actual and possible behavioral paths of the ha tchling crocodiles during the capture phase. During the release phase, the target hatchling would be held at shoreline for a minute before being released. Once again, the behavior flowchart of the target hatchling was separated from the siblings to better explain what occurred (Figure 3). Once the hatchling was released, it would vocalize before scurrying of into the water and swimming towards the den. This pattern occurred with all five releases. Like the capture phase, most or all the hatchlings were hidden, seeking refuge from the potential predator, so not all movements were observable. Releases A, B, C, had responses from the siblings. Releases D and E did not have sibling vocal responses, but in addition to release A , at least one of the siblings w as observed moving towards the distress calls of the captive hatchling. Capture B did not have any visible siblings to observe. Capture C had one sibling croc odile that changed head positions from a normal submerged position to an above water alert position.

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C rocodile hatchling distress call functions Ramireddy 6 ! Fig ure 3 : Flowchart showing actual and possible behavioral paths of the hatchling crocodiles during the release phase. The siblings reacted vocally and behaviorally during both phases : once in the capture phase with a noose stick and once in the release phase with a captive hatchling. Vocalization of hatchlings are not significantly associated with a human approach (Figure 4, Fisher exact test, p= 0.35). Therefore, whether a sibling vocalizes when fleeing does not depend on if the human is holding a captive or not. Figure 4: Contingency table if hatchlings vocalized when a human approaches . ( Fisher exact test, p= 0.35 ) Movement directionality of hatchlings are significantly associated with a human approach (Figure 5, Fisher exact test, p = 0.0063). The hatchling will move towards the human

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C rocodile hatchling distress call functions Ramireddy 7 ! only if the human is holding a captive hatchling. It always flees when the human d oes not have a captive. Figure 5: Contingency table on hatchling directional movement when a human approaches. Significant ( Fisher exact test, p = 0.0063 ) An acoustical analysis of the recordings using Raven 2.0 Software shows a spectrogram of the vocalizations of the hatchlings. The spectrogram of vocalizations generated by a hatchling are composed by multiple elements. There are three elements that can be found as six different combinations (Figure 6). Every call has the predom inant Element A. Element A starts at a higher frequency followed by downward sloping harmonics. Element B has upward sloping harmonics that end s at a higher frequency . Element C is a repeated set o f pulse s. Element B will always precede Element A. Element C can either precede or succeed Element A.

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C rocodile hatchling distress call functions Ramireddy 8 ! Figure 6 : Six s pectrogram s of various Crocodylus acutus distress call s composed of Elements A, B, and C.

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C rocodile hatchling distress call functions Ramireddy 9 ! For the instances where siblings would vocalize responses, there were many in the span of a few minutes. Four distress calls and five response calls were heard in the span of five seconds (Figure 7). Responses immediately preceded or succeeded a distress c all. Figure 7 : Spectrogram of a dialogue between captive hatchling distress calls and sibling hatchling response calls. Additional Capture Observation s Hatchling A G ilbert h caught the first crocodile hatchling in the nest, not the pool. Hatchling D The hatchlings were dispersed more than usual throughout pond 1 . Gilberth caught this hatchling with his bare hands. Hatchling E The hatchlings were dispersed more than usual throughout pond 2. Gilberth caught this hatchling with his bare hands. O bse rvational Results Both nests were found along the a partially dried up Rio Murcielago in Cuajiniquil, Costa Rica. The first nest was discovered on 11 May 2019 at 10:00 PM with two eggs and a hatchling inside. The second nest was discovered 12 May 2019 at 1 0:10 AM with no eggs, but the hatchlings in the pool were clearly larger supporting the idea that they hatched earlier. Nest 1 is approximately three meters from the resident pool. Nest 2 is about ten meters from the resident pool. Resident Pool 1 has the base of a fallen tree providing much of the refuge along with a few brushes growing over the pool ( A ppendix 2 ). Resident Pool 2 is much larger with a large trunk laying in the middle of the pool ( A ppendix 3 ). Much of the refuge is composed of roots and fallen branches of nearby trees. Large crocodile tracks were found near Nest 1 that measured 16 cm by 16cm. Based on ratios between claw sizes and body length it could be calculated that the crocodile was abou t 2.3m long (Hutton 1987). Pepe, the owner of the farm near the sites, confirmed the length of the mother of Nest 1 as roughly two meters. He stated that the mother of Nest 2 was roughly three and a half meters long. During my time observing, most hatchlings came out of the refuge of the fallen branches to sunnier spots in the pool or along the bank as the day progressed. I heard vocalizations when they scurried away from me as I approached the pool to change a camera or recording. I noticed

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C rocodile hatchling distress call functions Ramireddy 10 ! one time when a tiger heron flew by the pool 2 and landed on a nearby log. When this predator flew in, the hatchlings vocalized and dipped from their basking location on logs into the water. On 18 May 2019, a thunderstorm occurred, and no hatchlings were present in pool 1. However, I heard vocalizations that came from within the refuge during the thunderstorm for about thirty seconds. That was the only instance during the storm and no movements were recorded. D ISCUSSION Table 3: Summarizes whether the results support the original hypotheses and predictions. When the hatchling vocalized a distress call, the siblings responded and moved toward the captive hatchling: the response associated with the hypothesis that the distress ca ll of a hatchling crocodile ( Crocodylus acutus) has the function of requesting help from siblings (Table 3 ). In five of the five captures, the siblings vocalized, and moved towards the captive four of five times (Table 2). The siblings were noticeably aler t in one of the five captures and fleeing from the call two of the five times . These observations support two other h ypotheses that a distress call functions to alert siblings and warn siblings. A predator that could have attacked the holder of the hatchling never appeared , thus refuting its associated hypothesis (Table 3) . Despite never seeing a group form among siblings, t he low visibility through the refuge's vegetation cover prevented me from noticing if a group formed or not. There was n either a response nor an appearance from the mother of either den , but the hypothesis about requesting help from the mother is not necessarily refuted. It was assumed the mother s w ere hidden in their respective den because of certain evidence: personal accounts, tracks, and prey displaying crocodile eating methods. The proximity of dens to nests allows females to remain nearby and more effectively guard nests against predators. Dens may also serve as a refuge for hatchlings. Hatchlings readily enter dens to escape predators and at the Belize Zoo they were frequently observed with the female in the den (Platt 2000). A possible explanation include s that the mother s could have been sleeping during the captures. She could have heard the calls but chose to ignore it to reduce the potential risk it could take on itself. The mother s could have left the area and settled in other locations ot her than the re sident pools. The hatchlings fled their basking spot toward the refuge of fallen vegetation every time they were approached during the pre capture phase (Figure 1). This aligns with normal behaviors of prey when encountering a larger potential predator. However, the sib lings did not vocalize for two of the five approaches. In a total of 25 approaches to a pool, the hatchling s vocalized eleven times (Figure 4). This table combines approaches from the pre capture phase, release phase, and random approaches. Whether a sibli ng vocalizes when fleeing does not depend on if the human is holding a captive or not (Figure 4, Fisher exact test, p= 0.35). However, the vocalizations

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C rocodile hatchling distress call functions Ramireddy 11 ! emitted when approached with a captive were different than vocalizations emitted when approached withou t a captive hatchling. The former resulted in a single quick cry by multiple individuals that was vocalized immediately before they fled towards the refuge. The latter results more in a back and forth exchange between the siblings and the captive hatchling . There were multiple calls for a short duration by multiple siblings that occurred either immediately before or immediately after a distress call (Figure 7). During the release phase, the released hatchling scurried off into the pool towards the refuge f ive out of five times. This behavior makes sense as the hatchling has a chance to escape from the predator. It chose to go towards the safest location as the refuge of the fallen vegetation , fellow siblings and the den of the mother. Only in three occurren ces (A, B, C) was a response vocalized by the siblings, and oddly in three other occurrences (A, D, E) was a movement towards the captive recorded (Figure 3). Therefore, there is no direct relation between a sibling vocalizing a response and whether it moves towards the captive. However, the sibling's direction of movement is significantly correlated with a human approach (Figure 5, Fisher exact test, p = 0.0063). They only approach if the human is holding a captive hatchling whi is vocalizing distress calls. This is a significant finding because in all other cases, the hatchlings flee from the presence of a potential predator. The response to distress calls overrules the fear cre ated by a potential predator to a certain extent. The siblings never swam all the way up to meet the captive but would swim a considerable distance from safety to either learn more about the situation of the captive or to possibly assist. During the capture phase, two of the five captures (D, E) interestingly did not initially vocalize a distress call when captured (Figure 2) . A factor that could have influence this lack of vocalization was that b oth captures occurred at night . Perhaps the hatchlings chose not to vocalize whe n caught because the predator did not know what it had caught and could potentially let it go. Vocalizing would further confirm that the predator had caught some sort of prey, or more specifically, a crocodile hatchling. Once a hatchling was caught, four o f the five instances (A, C, D, E) resulted in at least one sibling crocodile moving in the direction of the captive and a response in all five instances . Despite a potential predator in the vicinity, the movement towards the captive further supports the hy pothesis that the distress calls are to elicit help from fellow siblings. The capture phase begins once a hatchling is captured and ends when the hatchling is brought back to the shoreline. A notable observation was that not all hatchlings would vocalize on the transport to the resid ent pool or even at the shore. R ather, every crocodile would vocalize when brought to the level of the pool. This could be because the crocodile hatchlings have better understandings and more accommodated to a pool level view. Crocodiles have a fovea (a depression in the retina where there is a high density of photoreceptors that provide a high resolution view of the world) that stretches across the back of the eye in line with the horizon (Nagloo 2016). This adaptation proves vital to the stalking predation tactic of crocodiles where only the eyes and nostrils are above water. It allows them to scan the shore at water level for possible prey. However, once the hatchling was raised, it had a new unnatural horizon of air and vege tation. Once it was lowered, the hatchling would be able to see a more memorable environment and understand that there was now a much more likely escape path ( through the pool water ) which w ould lead to vocaliz ations in search of help. Once the hatchling w as

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C rocodile hatchling distress call functions Ramireddy 12 ! released, it wo uld vocalize before scurrying into the water and swimming towards the den , a pattern that occurred in all five releases. An acoustical analysis of the recordings using Raven 2.0 Software shows a spectrogram of the vocalizations of the ha tchlings. Further analysis shows the acoustical shape of a distress call ( E lement A) in all vocalizations of the captive. However, additional harmonics or pulses were found before or after each Element A. These additional elements, B and C, created a total of six possible variations of a distress call that were found throughout the r ecordings. The purpose of vary ing the distress call does not seem to be understood as no notable observations were made in relation to these call variations. Sibling responses f requency (Hz) or likelihood did not alter between the variations. More research regarding the elements and their function is needed. When analyzing the responses in relation to the distress calls, the difference in timing of a response call to a distress c all is much shorter than the timing difference between two distress calls. Not every distress call received its own response (Figure 7) . The frequency of the responses was much lower than the frequency of distress calls. The microphone was held much closer to the captive than to the siblings. This resulted in more harmonics on the spectrogram for the distress calls than for the responses. The distance of the microphone influences the maximum frequency of the call, but not the fundamental frequency. Analyzing the harmonics of the response call, it seemed to fit into the category of distress calls rather than contact calls or either of the other possible categories (Figure 8). The response has downward sloping harmonics that are a key characteristic of only distress calls. Further research with more data po ints will be vital to confirm this categorization. It is a potentially exciting discovery if the siblings responded to a distress call with distress calls of their own. Desp ite being in a safe state, emitting a distress call could have the motive of echoing the call of the captive to the rest of the hatchlings and possibly the mother as well. T his could help explain why some siblings move towards the call: to shorten the dist ance between the captive and the rest of the group, creating a communication bridge from the captive to the rest of the group. Figure 8 : Comparison of response spectrogram (left) and distress call s pectrogram (right) of a juvenile Nile crocodile ( Vergne 2009; Fig. 2C).

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C rocodile hatchling distress call functions Ramireddy 13 ! A CKNOWLEDGEMENTS Warm thanks to Gilberth A mpie and Andres Ampie for finding the nest and observing the spark for my research project. Many more thanks to G ilbert h for his time, dedication to help wherever and whenever possible, and ability to captur e crocodiles with bravery and ease despite the presence of a mother. Many t hanks to Frank Joyce for sharing his intelligence, wit, jokes, guidance and willingness to push me past my limits to produce the best work I could muster. Thank you to Emi Triana for the plethora of knowledge regarding acoustical analysis and the insights I would not have been able to come across was it not for her. Thank you to Pepe for allowing us to use his farm as a research site. A final t hank you to the Mon teverde Institute for the hospitality and resources needed to complete this research project. L ITERATURE CITED Bradbury, J. W. & Vehrencamp, S. (1998). Principles of Animal Communication. Sinauer Associates, Sunderland Britton, A. R. C. (2001). Review and Classification of Call types of Juvenile Crocodilians and Factors affecting Distress Calls. In Crocodilian Biology and Evolution (Ed. G. C. Grigg, F. Seebacher and C. E. Franklin), pp. 364 Ð 377. Surrey Beatty & Sons, Chipping Norton. Coombs, J. (1982). Juv enile specimens of the ornithischian 25, dinosaur Psittacosaurus. Paleontology 89 Ð 107. Gorzula, S. J. (1978). An ecological study of Caiman crocodilus inhabiting savana lagoons in the Venequelan Guyana. Oecologia 35, 21 Ð 34. Herzog, H. A. & Burghardt, G. M. (1977). Vocalization in 44, juvenile crocodilians. Herpetologica 294 Ð 303. Hutchinson, John. "Archosaur Lineage (ÔFamily Tree')." Dawndinos Testing the Locomotor Superiority Hypothesis for Early Dinosaurs, 2019, dawndinos.com/. Hutton, J M. "Morphometrics and Field Estimation of the Size of the Nile Crocodile ." African Journal of Ecology, vol. 25, 1987, pp. 225 Ð 230. Kettler, Lutz, and Catherin E Carr. "Neural Maps of Interaural Time Difference in the American Alligator: A Stable Feature in Modern Archosaur s." Journal of Neuroscience , vol. 39, no. 20, 15 May 2019, doi:https://doi.org/10.1523/JNEUROSCI.2989 18.2019. Nagloo, Nicolas, et al. "Spatial Resolving Power and Spectral Sensitivity of the Saltwater Crocodile, Crocodylus p orosus , and the Freshwater Crocodile, Crocodylus j ohnstoni ." Journal of Experimental Biology, vol. 219, 2016, pp. 1394 Ð 1404. Norell, M. A., Clark, J. M., Chiappe, L. M. & Dashzeveg, D. 378, (1995). A nesting dinosaur. Nature 774 Ð 776. Platt, Steven G. "Dens and D enning Behavior of Morelet's Crocodile ( Crocodylus m oreletii )." Amphibia Reptilia, vol. 21, no. 2, 2000, pp. 232 Ð 237.

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C rocodile hatchling distress call functions Ramireddy 14 ! Romero, G. A. (1983). Distress call saves a Caiman Caiman 15, crocodilus hatchling in the Venezuelan Llanos. Biotropica 71. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. London: University of Chicago Press. Smith, Dave. "The Great Archosaur Lineage." The Archosauria, 26 Oct. 2005, ucmp.berkeley.edu/diapsids/archosauria.html. Stephens, Tim. "Scientists Reconstruct Genome of Common Ancestor of Crocodiles, Birds, Dinosaurs." UC Santa Cruz News, 11 Dec. 2014, news.ucsc.edu/2014/12/crocodile genomes.html. Varricchio, D., Jackson, F., Borkowski, J. & Horner, J. (1997). Nest and egg clutches of the dinosaur Troodon fromosus and th e 385, evolution of avian reproductive traits. Nature 247 Ð 250. Vergne, Amelie L, et al. "Acoustic Communication in Crocodilians: from Behaviour to Brain." Biological Reviews, vol. 84, 2009, pp. 391 Ð 411., doi:10.1111/j.1469 185X.2009.00079.x. Wesolowski, T. (2004). The origin of parental care in birds: 15, a reassessment. Behavioral Ecology 520 Ð 523.

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C rocodile hatchling distress call functions Ramireddy 15 ! APPENDIX Appendix 1: A cladogram that depicts the lineage of the Phylum Archosauria (Hutchinson 2019) Appendix 2: Resident Pool 1 with about 12 hatchlings swimming

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C rocodile hatchling distress call functions Ramireddy 16 ! Appendix 3: Resident Pool 2 Appendix 4: Side and top view of Captive Hatchling C

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C rocodile hatchling distress call functions Ramireddy 17 ! Appendix 5: Close up of Captive Hatchling C head Appendix 6: Ventral side of Captive Hatchling C

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C rocodile hatchling distress call functions Ramireddy 18 ! Appendix 7: Crocodiles, Crocodylus acutus , encountered in Cuajiniquil


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