Bioacoustics of Megatibicen harenosus

Male calling song description and behavioral observations. Megatibicen harenosus is apparently the only Megatibicen species with adult activity in the Mescalero-Monahans dunes during late summer and fall (pers. obs.). During observations at the type locality, males produced calling songs in late morning between 1050–1120 h. Males typically employed sing-fly behavior, in which a given male produced one bout of song from any given location followed by a short flight to a new location for another bout of song. Individual males produced as many as three bouts in a single location, and these bouts were separated by a variable interval of 5 s to 51 s. Calling song bouts consist of a single brief phrase (19.1± 5.4 s ) that is amplitude and frequency modulated ( Fig. 3 A-C). Dorsoventral undulation of the abdomen ( Cole 2008 ; Sanborn & Phillips 2004 ; Stucky 2013 ) produces alternating high amplitude peaks and a low amplitude troughs ( Fig. 3 B). Both peak and trough are of similar duration: 29.1±4.0 ms and 26.4±3.4 ms, respectively. The period of amplitude modulations is 55.2±2.9 ms and the syllable repetition rate is 17.7± 1.0 s -1 ( Fig. 3 B). The frequency range of the peak (2.7–14.7 kHz) is broader than that of the trough (2.9–10.4 kHz), and the frequency at maximum amplitude is 5.8±0.5 kHz ( Fig. 3 C). The calling song structure of M. harenosus lacks the often prolonged, unmodulated introductory and concluding phrases found in M. tremulus . The fine scale syllable structure also differs ( Fig. 3 B–E). Significant correlations were found between durations of the modulated trough and modulated peak (r = 0.91, p <0.0001), as well as between the duration of the modulated trough and both syllable period (r = 0.67, p = 3.3 × 10-3) and syllable repetition rate (r= -0.73, p = 9.0 × 10-4). Syllable period and syllable repetition rate are mathematically related and were therefore strongly correlated (r = -0.89, p <0.0001). Response variables for MANOVA were thus pared down to three independent characters: duration of the modulated peak, frequency, and syllable repetition rate. Using these three characters as response variables, the null hypothesis that song character means do not differ between M. harenosus and M. tremulus was rejected ( p = 4.538 × 10-4). In M. harenosus songs the syllable repetition rate is faster ( p = 7.359 × 10-3) with a correspondingly shorter syllable period, and the duration of the high amplitude peaks is longer ( p = 4.245 × 10-4) with correspondingly shorter low amplitude trough compared with M. tremulus . Frequency at maximum amplitude did not differ between the two species ( p = 6.36 × 10-2). Calling songs of New Mexico and Texas M. harenosus populations were not significantly different ( p = 0.221). Example songs will be posted in the BioAcoustica online repository (Natural History Museum, London; www.bio.acoustica.com).