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Fandel, Amber Desneige
Sealizacin vocal en Henicorhina leucosticta (Troglodytidae)
Vocal signaling in Henicorhina leucosticta (Troglodytidae)
The communication between organisms has long been a fascination of mankind. Birds have been the subject of many such studies as they commonly have a large repertoire of communication techniques. This study examines the changes in several song measurements in order to determine the vocal responses of the breeding pairs to playbacks
of various con-specifics. The researcher found that using measurements of low, high, center, maximum, and delta frequency of each pair before and after a playback, the pairs were easily differentiated from one another
(Wilks != 0.61629, F20.455=3.57, p<0.001). Following playbacks, all pairs evaluated showed a decrease in maximum frequency of song phrases and a narrowing of frequency ranges (smaller delta frequency). Such changes in song characteristics may function to make the singing pair sound larger to intruders or to decrease call interference and the distance that the call travels.
La comunicacin entre los organismos ha sido desde hace mucho tiempo de inters para la humanidad. Las aves han sido un tema de estudio en este campo debido a su gran variedad de repertorios utilizados para la comunicacin. En este estudio examine los cambios en varias medidas de las vocalizaciones para determinar la respuesta vocal de las reproducciones de las parejas de varios conspecficos.
Text in English.
Aves que cantan--Vocalizacin--Costa Rica
Tropical Ecology 2009
Ecologa Tropical 2009
t Monteverde Institute : Tropical Ecology
Vocal Signaling in Henicorhina leucostict a (Troglody tidae) Amber Desneige Fandel Department of Biology, Occidental College ABSTRACT The communication between organisms has long been a fascination of mankind. Birds have been the subject of many such studies as they commonly have a large repertoire of communication techniques. This study examines the changes in several song measurements in order to determine the vocal responses of the breeding pairs to playbacks of various con specifics. The r esearcher found that using measurements of low, high, center, maximum, and delta frequency of each pair before and after a playback, the pairs were easily differen tiated from one another (Wilks = 0.61629, F 20.455 =3.57, p<0.001 ). Following playbacks, all pairs eva luated showed a decrease in maximum frequency of song phrases and a narrowing of frequency ranges (smaller delta frequency). Such changes in song characteristics may function to make the singing pair sound larger to intruders or to decrease call interferen ce and the distance that the call travels. RESUMEN La comunicaciÂ—n animal desde hace mucho tiempo ha sido de interÂŽs para la humanidad. Las aves han sido un modelo de estudio en este campo debido a su gran variedad de repertorios utilizados para la comuni caciÂ—n. En este estudio examinÂŽ los cambios en varias medidas de las vocalizaciones para determinar la respuesta vocal de parejas al playback de varios conspecificos. EncontrÂŽ que cuantificando la frecuencia mas baja, la mas alta, la central, la mÂ‡xima y el rango de frecuencias, las parejas pueden ser identificadas acÂœsticamente (Wilks lambda= 0.61629, F 20.455 =3.57, p<0.001). DespuÂŽs de ser expuestos al playback, todas las parejas disminuyeron la frecuencia y estrecharon el rango de sus vocalizaciones. Est os cambios en la estrucura de las vocalizaciones pueden funcionar para que la pareja que emite el canto aparente un mayor tamaÂ–o a los intrusos o para evitar la atenuaciÂ—n de la seÂ–al. INTRODUCTION Communication is a necessary trait in nearly all organis ms and each goes about this behavior in a slightly different manner The evolution of communication between individuals required a signaler, a signal, and a receiver (Alcock 2005) In order for the signal to fulfill its purpose (that of communicating to an other individual), the signaler must emit a signal that can be interpreted by the receiver. Ideally this signal, which can be costly for the organism to produce, will elicit a certain response from the receiver ( Alcock 2005 Laidre and Venrencamp 2008, Mur ray 1971, Orians and Willson 1964, Price et al. 2005 ). Certain frequencies of sound are more difficult to produce than others and have different functions ( Fitzpatrick et al. 1977, Laidre and Venrencamp 2008, Price et al. 2005). From the perspective of the perspective of the evolution of effective communication in organisms, the examination of these characteristics is important. C ommunication in birds has been widely studied due to the relative ease of studying birds as well as the great knowledge of phyl ogeny, species assignment, and natural history of this taxon Birds are known for the wide variety of their songs between species, ranging from very complex and beautiful to quite dissonant and unpleasant to completely atonal noises ( Fitzpatrick et al. 197 7, Salaman et al. 2003, Skutch 1940). Extensive studies have been performed on many
!"#$%&' ( ! species to determine and characterize the function of their many songs and calls ( Fitz gerald et al. 1977, Kennedy and White 1996, Laidre and Venrencamp 2008 Marshall Ball et al. 2006 ) In nearly all species, the function of these vocalizations and the physical cues that go along with them serve to communicate territory boundaries, signal the opposite sex dur ing courtship, and communicate between individuals of a group ( Alco ck, 2005, Laidre and Venrencamp 2008, Marshall Ball et al. 2006, Salaman et al. 2003, Skutch 1940 ) All of the song s and calls vary according to individual, species, and location ( Dingle and Slabberkoorn 2008, Fitzpatrick et al. 1977 Ryan and Brenowitz 19 85 ) Some bird species maintain stable territories throughout the year which affects the function of songs ( Ashmole 1968, Fitzpatrick et al. 1977, Salaman et al. 2003, Skutch 1940) For many species that have stable territories, communication is either to inform other individuals in surrounding territories the location of the territory of the sender or functions to maintain con tact between the other member ( s ) of the nest ( Alcock 2005 Ashmole 1968, Fitzpatrick et al. 1977 ) Continued interaction between the groups occupy ing surrounding territories is necessary for territorial signaling to be efficient and elicit the proper response from both sender and receivers (McGregor 1993). In some studies, it has been shown that t he presence o f a con specific has re sulted in an increase in song complexity when compared to a spontaneous call from the sender ( Dunn 2006, Kennedy and White 1996, Laidre and Venrencamp 2008, Ryan and Brenowitz 1985 ) Maintaining contact among pairs is necessary between individuals in a pair during foraging especially for those that forage in the undergrowth, as visibility is usually low in such areas ( Fitzpatrick et al. 1977, Salaman et al. 2003, Skutch 1940). Henicorhina leucosticta will be used i n order to illuminate the changes in song characteristics of bird pairs to (1) neighboring con specifics and (2) an unknown con specific Previous studies have concluded that songs with lower frequencies indicate higher hostility then those of higher frequencies (Morton 1977), and H. leucosticta are expected to lower frequency accordingly in response to territory invaders. The song characteristics of Henicorhina leucosticta responses to playback have been relatively un examined T his study aims to add to the lack of information on this species in the Monteverde area specifically In order to examine song changes with the introduction of playback, i ndicative song characteristics such as low, hig h, maximum, and delta frequency will be examined. These qualities are related to the function of the song MATERIALS AND METHODS Study site and species Henicorhina leucosticta the Gray breasted wood wre n is a comm on understory birds along the mountainside of the cloud forest in the Monteverde area of Costa Rica Henicorhina leucosticta roos t in pairs, h ave distinct, constant territories throughout the year, and are usually found foraging within a short distance from their nest or roost site ( Fitzpatrick et al. 1977, Garrigues 2007, Salaman et al. 2003, Skutch 1940) Tropical w rens are known to sing all y ear round desp ite seasonal and daily weather conditions ( Fitzpatrick et al. 1977, Garrigues 2007, Salaman et al. 2003, Skutch 1940). Henicorhina leucosticta also participates in duetting, in which both members of the pair sing ( Fitzpatrick et al. 1977, Garr igues 2007, Salaman et al. 2003, Skutch 1940) This calling functions as both communication between the breeding pairs and signal territory locations between pairs in surrounding areas.
!"#$%&' ) ! This study wa s performed between 155 0 and 1650 meters above sea lev el on the Sendero Principal behind the Estacion Biologica Monteverde during April and May The l ocations of the territories of 3 pairs of H. leucosticta were located by their territorial calling in the early morning (0500 0700 hours) and locations were aff irmed using approaches in response to the Voices of Costa Rican Birds CD Gray Breasted Wood Wren playback. Playbacks were emitted using JBL portable speakers attached to an Apple iPod between the hours of 0500 and 0800 within the territory of the pair. Sa mpling methods and data analysis The researcher recorded the songs of H. leucosticta pairs with a Macally iVoicePro microphone attached to an Apple iPod. Spontaneous songs were recorded upon arrival to a territory from the pairs before the playback was emi tted. After one minute of recording spon taneous song the playback was produced to the pair while recording continued until up to two minutes after the playback ( if the pairs continued to sing following the playback ) Recordings from the Voices of Costa Ri can Birds CD were primarily used for playback data Five days of two recordings on each pair were gathered using playback. The researcher allowed between twenty minutes and one and a half hours between each recording of a pair to minimize the influence of the previous trial. The recordings were then down loaded into Raven Interactive Sound Analysis Software. From these recordings, a portion of the song of each of two pair s were isolated and amplified. These amplification s of each of the two pair s were saved as a new file in Raven and then transferred back onto the iPod. Using the is olated song from the pairs, the selection of approximately one minute for each pair (the time of the original CD playback) was then used as the playback. Playbacks of the pairs wh ose songs were isolated (only pair 2 and 4) were then used as playbacks for each of the three pairs. A total of six trials of each of the pair playbacks and ten trials of the CD playback were performed. All of the recordings obtained for the three pairs we re entered in the Raven Software and analyzed. In order to determine the characteristics of each pair's song and the differences in these characteristics of their songs before and after playback, song phrases were isolated within Raven If possible, five song phrases before and after the playback were isolated for each recording from each pair and each trial For every selection, measurements of high, low, center, max imum and delta frequency were taken. Maximum frequency indicates the point where the most energy of the song phrase is concentrated. The other measures are those that indicate relative frequency and changes of characteristics throughout the song. To determine differences between pairs regardless of the playback a Multivariate Discriminate Ana lysis was performed. In order to determine if there was a change in song characteristics before and after playbacks, paired t tests were used. RESULTS Analyses were performed to determine if the pairs were differentiable based on their song characterist ics. Using the characteristics of low, high, center, max, and delta frequency, the pairs were easily differentiated from one another prior to playback (Wilks = 0.61629, F 2 0 .455 =3.57, p<0.001). It was also found that by examining these measurements taken o n the songs of pairs
!"#$%&' ! before the playback, the pair c ould be determined with a 61.76% accuracy using a Multivariate Discriminate Analysis. The song phrases isolated from each pair were examined to determine if differ ences in characteristics before and afte r playback were present. General trends were observed, but these results were shown to be largely statis tically non significant (t test p>0.05). FIGURE 1. Average maximum frequency for H. leucostica pairs 2, 4, and 5 before and after playbacks from t he Voices of Costa Rican Birds CD, pair 2 and pair 4. Error bars indicate standard error. B oth pair 2 and pair 5 lowered their maximum frequency in repsonse to playback (Fig.1) O nly pair 4, whose frequency before the playbacks was already quite a bit lowe r than pair 2 and 5, raised its frequency. Figure 2. Average delta frequency for H. leaucostica pairs 2, 4, and 5 before and after playback from the CD, pair 2, and pair 4. Error bars indicate standard error.
!"#$%&' + ! Each of the pairs narrowed their range of f requ encies within their song phrases in response to playback with the exception, again, being pair 4, who already had relatively low delta frequency. DISCUSSION This study aimed to examine the changes in certain song characteristics before and after a pla yback of a con specific was presented. Clear differences between the songs of individuals within the few pairs of H. leucosticta were found. These findings indicate that though individual pairs are easily identifiable while they are spontaneously singing, once a playback is used the songs are not differentiable between pairs. These findings suggest that spontaneous singing of a pair performs a different function than the song that was recorded following a co n specific playback. P revious studies have shown that most birds have a large repertoire of calls that perform varying functions ( Fitzpatrick et al. 1977 ) The function of the spontaneous calling can be reasonably concluded to be communication between the members of a territorial pair during foraging and mate location and each pair has its own repertoire that it uses to communicate and ensure the identity of its mate. The songs that can not be differentiated bet ween pairs upon presentation of a threat within the pair's territory (the presence of a con sp ecific but not breeding partner call) probably can be concluded to serve as warning calls among con specifics These warning calls are desired to drive the intruder out of the territory T he general function of the response to the playback as one of terr itoriality may be the reason for the decreases in the maximum frequencies of calls as well as the narrowing of frequency ranges in calls that were observed All songs seem to converge to a l ower and smaller range of frequencies when an intruder was detecte d in a territory of H. leucosticta pair These findings may provide further support for Morton's (1977) findings that lower frequencies confer larger body size. As lower sounds require more energy to produce, only larger birds can reach certa in lower frequ encies ( Price et al. 2006 ) T he observed lowering of frequencies may express a desire of the members of the pair to appear larger to the intruder. Many studies have observed the emission of lower frequencies during a sort of competition between individuals ( Laidre and Venrencamp 2008, Morton 1977 Price et al. 200 6 Ryan and Brenowitz 1985). In addition to being correlated to large body size, lower frequencies travel farther and with lower interference than higher frequencies ( Alcock 2005 Price et al. 2006 Ryan and Brenowitz 1985) Lower maximum frequency and lower ranges of frequencies may be utilized to communicate over longer distances, ensuring that intruders at varying distances from the pair receive the warning signal. Smaller frequency ranges have a lso been found to make location of the pairs by predators more difficult (Alcock 2005 ). These alterations in song characteristics depend on the exact function of the call, whether it is to confuse predators that may be mimicking a con specific call or to increase the likelihood that the warning call reaches the intruder (McGregor 1993) It is certain though, that there is a trend of change for the calls of H. leucosticta following presence of an intruding con specific, though the sample size of this study was too small to indicate significant changes. The researcher believes that a variety of questions still remain to be answered about the behavioral response of H. leucosticta to con specific playbacks. Future studies could address the time and distance to approach by the pairs to the location of the playback and how this behavior differs depending on the familiarity of the con specific call used. A similar experiment to the one
!"#$%&' ! performed here could be done using con specific songs from pairs at varying dis tances from the pair's territory. Additional studies should also be completed in response to the dear neighbor theory ( Hyman 2005 ) determining if responses differ between various playbacks used. The function of a s ignal is useful only if this function ca n be proper ly interpreted by its receiver. As most organisms do not communicate only one piece of information and do not aim to communicate with only one organism, repertoires of communicative devices have developed. Changes in song function should incur c hanges in song structure and characteristics. The results found here indicate that pairs may desire to appear large r o r to send their signals farther by lowering their delta and maximum frequency as a territorial response to con specific intruders. This in fers that the receiver of the signal, whoever that may be, can interpret this change. Results of this study also further show the differentiation of calls of individuals within a species and the overall trend toward a general warning call within the specie s. AC KNOWLEDGEMENTS I would like to thank Anjali Kumar for her continued efforts to assist me in my research endeavors and her enthusiasm and encouragement I would also like t o give numerous thanks to Yi men Araya for his many hours teaching me about my birds, for his continual support throughout numerous technological mishaps, and for his extensive knowledge on statistics, without which I would be completely lost. Finally I would like to thank the CIEE Costa Rica, Monteverde program staff for the use of their equipment and trails and for providing me this amazing opportunity to study in a tropical paradise
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