Determinants of the acoustic behaviour of red deer during breeding in a wild alpine population, and implications for species survey

Abstract

A necessary step in the application of animal communication studies to population ecology involves quantitative descriptions of acoustic variation within individuals. Stereotypy is in fact fundamental to allow individual recognition based on call structure and, in turn, to establish the number of different calling individuals in a population (complementing censuses), or to track individuals through years by the acoustic characteristics of their signals (complementing monitoring). Here we centred on the acoustic behaviour of red deer stags during reproduction to analyze its ecological determinants and to test whether calls are individual specific. Scanty information is available on how day time and weather may affect red deer acoustic activity, and whether spectrotemporal analyses of calls could permit to discriminate among different individuals. We centred on roars, the loud repeated calls given by stags throughout the rut, in a mountainous forest habitat, over two rutting seasons. Significant inter-annual differences were found in the duration of the roaring period and in the magnitude of roaring rates. Roaring rate dropped in the wettest days, suggesting that counts by ear may be biased by changeable environmental conditions within and among breeding seasons. By analysing the spectrotemporal features of roars, we found that several spectro-temporal variables varied more among than within individuals. Discriminant analysis classified a posteriori the 72% of the calls to the individuals that uttered them, and the fundamental frequency was the acoustic parameter that best discriminated individuals. Therefore, in areas in which visual information is limited by habitat characteristics, surveys by ear should be performed in dry weather and over several nights to well cover the roaring period. This count method could be complemented by spectrografic analysis of Acoustic activity and stereotypy in red deer 53 stag call bouts to assist in censusing populations and reduce the probability of double counts when stags are moving.

Spring spotlight counts provide reliable indices to track changes in population size of mountain‐dwelling red deer Cervus elaphus

“…Mazzarone et al (1991), per le Foreste Casentinesi, hanno riscontrato che il picco della frequenza dei bramiti si colloca nell'ultima settimana di settembre nelle ore comprese tra le 21 e le 24 e tra le 3 e le 6. Bocci et al (2012) indicano che l'attività di bramito mostra un picco 5-7 ore dopo il tramonto.…”

“…La necessità di effettuare una o più repliche è evidenziata anche da Bocci et al(2012), che suggeriscono che l'analisi spettrografica dei suoni emessi durante il periodo del bramito potrebbe migliorare l'applicazione di questo metodo, evitando doppi conteggi di maschi in bramito che si spostano durante la sessione di rilevamento.…”

Vocal activity and acoustic structure of the rutting calls of Siberian wapiti (Cervus elaphus sibiricus) and their imitation with a hunting luring instrument

“…As a consequence, vocalizations of Siberian wapiti are much more similar to those of American wapiti than to European red deer (Tembrock, 1965;Nikolski & Wallschlager, 1983;Volodin et al, 2013). European red deer stags produce low-pitched roars with fundamental frequency (f0) ranges from 40 to 380 Hz: Corsican C. e. corsicanus Erxleben, 1777 (mean f0 = 40 Hz: Kidjo et al, 2008); Scottish C. e. scoticus Lonnbert, 1906 (mean f0 = 107 174 Hz: Long et al, 1998;Reby & McComb, 2003); Iberian C. e. hispanicus Hilzheimer, 1909 (mean f0 = 180 186 Hz: Frey et al, 2012;Passilongo et al, 2013); C. e. hippelaphus Erxleben, 1777 (maximum f0 = 273 Hz: Bocci et al, 2013). In contrast, the available data for American and Siberian wapiti suggest produce high-pitched bugles with an f0 above 1000 Hz: Siberian wapiti from Altai C. e. sibiricus (Nikol skii, 2011); Canadian wapiti C. e. canadensis (Struhsaker, 1968); Roosevelt wapiti C. e. roosevelti Merrian, 1897 (Bowyer & Kitchen, 1987), Tule wapiti C. e. nannodes Merriam, 1905(Volodin et al, 2013 and Rocky Mountain wapiti C. e. nelsoni Bailey, 1935 (Feighny et al, 2006;Frey & Riede, 2013).…”

Vocal activity of the red deer and the acoustic structure of its rutting calls in the Russian Far East

“…The effect of temperature on the vocal activity of stags in the wildlife Alpine population was also absent [13], while a 31 year study in France has demonstrated a negative correlation between ambient temperature and the counted rutting calls. This is explainable by a decrease in animal activity with increase in temperature [11].…”

“…In the Alpine population (Italy), stags mainly roared in the night and early morning (5 a.m. to 7 a.m.) [13]. However, the stags of the Isle of Rum red deer [14] roared mainly during daytime, as did farmed red deer stags in France [15].…”