Rutting vocal display in male impala (Aepyceros melampus) and overlap with alarm context

Abstract

Background The rutting vocal display of male impala Aepyceros melampus is unique for its complexity among ruminants. This study investigates bouts of rutting calls produced towards potential mates and rival males by free-ranging male impala in Namibia. In particular, a comparison of male rutting and alarm snorts is conducted, inspired by earlier findings of mate guarding by using alarm snorts in male topi Damaliscus lunatus. Results Rutting male impala produced 4–38 (13.5 ± 6.5) rutting calls per bout. We analyzed 201 bouts, containing in total 2709 rutting calls of five types: continuous roars produced within a single exhalation-inhalation cycle; interrupted roars including few exhalation-inhalation cycles; pant-roars distinctive by a pant-phase with rapidly alternating inhalations and exhalations; usual snorts lacking any roar part; and roar-snorts starting with a short roar part. Bouts mostly started and ended with usual snorts. Continuous roars were the shortest roars. The average duration of the exhalatory phase was longest in the continuous roars and shortest in the pant-roars. The average fundamental frequency (49.7–51.4 Hz) did not differ between roar types. Vocal tract length, calculated by using measurements of the first four vocal tract resonances (formants), ranged within 381–382 mm in all roar types. In the studied male impala, rutting snorts within bouts of rutting calls were longer and had higher values of the upper quartile in the call spectra than alarm snorts produced towards potential danger. Conclusions Additional inhalations during the emission of the interrupted and pant-roars prolong their duration compared to the continuous roars but do not affect the fundamental frequency or the degree of larynx retraction while roaring. Alarm snorts are separated from one another by large intervals, whereas the intervals between rutting snorts within bouts are short. Sometimes, rutting snorts alternate with roars, whereas alarm snorts do not. Therefore, it is not the acoustic structure of individual snorts but the temporal sequence and the occasional association with another call type that defines snorts as either rutting or alarm snorts. The rutting snorts of male impala may function to attract the attention of receptive females and delay their departure from a male’s harem or territory.

Male impala (Aepyceros melampus) vocal activity throughout the rutting period in Namibia: daily and hourly patterns

“…This is a native Namibian habitat with approximately 60% bush cover and open areas around artificial watering places. In 2015, it accommodated about 800 free‐ranging impalas originating from about 100 individuals released in 1994 (Frey et al, 2020; Volodin et al, 2021).…”

“…A clearly defined rutting period exists only in regions of Africa with prominent seasonal changes of temperature, day length and rainfall, as, for example, in Zimbabwe (Murray, 1982;Warren, 1974), South Africa (Oliver, 2002;Oliver et al, 2006) and Namibia (Frey et al, 2020;Volodin et al, 2021). In such a temperate climate, rutting male impala produce their bouts of rutting calls in May-June, depending on the latitude (Dasmann & Mossman, 1962;Fairall, 1983;Frey et al, 2020;Mason, 1976;Oliver, 2002;Oliver et al, 2006;Volodin et al, 2021). During the rutting period, males keep territories rich in food and/or water resources of about 34 ha (Oliver, 2002;Oliver et al, 2006) that attract females, and defend them against rival males (Anderson, 1972a(Anderson, , 1972b(Anderson, , 1975Frey et al, 2020;Jarman, 1979;Leuthold, 1970;Murray, 1982;Oliver, 2002;Oliver et al, 2006;Volodin et al, 2021).…”

“…In such a temperate climate, rutting male impala produce their bouts of rutting calls in May-June, depending on the latitude (Dasmann & Mossman, 1962;Fairall, 1983;Frey et al, 2020;Mason, 1976;Oliver, 2002;Oliver et al, 2006;Volodin et al, 2021). During the rutting period, males keep territories rich in food and/or water resources of about 34 ha (Oliver, 2002;Oliver et al, 2006) that attract females, and defend them against rival males (Anderson, 1972a(Anderson, , 1972b(Anderson, , 1975Frey et al, 2020;Jarman, 1979;Leuthold, 1970;Murray, 1982;Oliver, 2002;Oliver et al, 2006;Volodin et al, 2021). But in the tropical climate of Eastern Africa, impala breed year-round and dominant impala males constantly herd females and defend them against rival males, at low levels of roaring activity (Leuthold, 1970;Schenkel, 1966).…”

“…In impala, the timing of the rut differs between temperate and tropical climate zones. A clearly defined rutting period exists only in regions of Africa with prominent seasonal changes of temperature, day length and rainfall, as, for example, in Zimbabwe (Murray, 1982; Warren, 1974), South Africa (Oliver, 2002; Oliver et al, 2006) and Namibia (Frey et al, 2020; Volodin et al, 2021). In such a temperate climate, rutting male impala produce their bouts of rutting calls in May‐June, depending on the latitude (Dasmann & Mossman, 1962; Fairall, 1983; Frey et al, 2020; Mason, 1976; Oliver, 2002; Oliver et al, 2006; Volodin et al, 2021).…”

“…In polygynous ruminants, vocal activity represents an important part of male advertising behaviour in the rutting period (Briefer et al, 2010;Clutton Brock & Albon, 1979;Frey et al, 2007aFrey et al, , 2007bFrey et al, , 2011Frey et al, , 2012Golosova et al, 2017;Jarman, 1979;Volodin et al, 2019). Impala (Aepyceros melampus) are polygynous ruminants with impressive male rutting displays including complex behaviour (Frey et al, 2020) and bouts of rutting calls including different types of roars and snorts (Volodin et al, 2021). In other studied polygynous ruminants, the rutting periods are known to have a strict seasonality (Rusin et al, 2019(Rusin et al, , 2021Volodin et al, 2013Volodin et al, , 2015Volodin et al, , 2016Yen et al, 2013).…”