Variability of Female Responses to Conspecific vs. Heterospecific Male Mating Calls in Polygynous Deer: An Open Door to Hybridization?

Males of all polygynous deer species (Cervinae) give conspicuous calls during the reproductive season. The extreme interspecific diversity that characterizes these vocalizations suggests that they play a strong role in species discrimination. However, interbreeding between several species of Cervinae indicates permeable interspecific reproductive barriers. This study examines the contribution of vocal behavior to female species discrimination and mating preferences in two closely related polygynous deer species known to hybridize in the wild after introductions. Specifically, we investigate the reaction of estrous female red deer (Cervus elaphus) to playbacks of red deer vs. sika deer (Cervus nippon) male mating calls, with the prediction that females will prefer conspecific calls. While on average female red deer preferred male red deer roars, two out of twenty females spent more time in close proximity to the speaker broadcasting male sika deer moans. We suggest that this absence of strict vocal preference for species-specific mating calls may contribute to the permeability of pre-zygotic reproductive barriers observed between these species. Our results also highlight the importance of examining inter-individual variation when studying the role of female preferences in species discrimination and intraspecific mate selection

Ambient noise monitoring in the Southern Ocean applying EU good environmental status descriptors

Concerns regarding the acoustic quality of habitats have increased over the past years. Within the EU Marine Strategy Framework Directive, this has led to the proposal of environmental status indicators for underwater noise levels. One indicator, based on 1/3- octave band levels at 63- and 125-Hz, intends to monitor anthropogenic noise, particularly from shipping. In this context, ambient noise is defined as the acoustic energy not assignable to a specific source. We applied this indicator to passive acoustic underwater recordings from the Southern Ocean, which represents an environment relatively void of anthropogenic noise. To collect multi-year passive acoustic data, two autonomous underwater recorders were deployed in the Weddell Sea at 0°W/E 66°S and 0°W/E 69°S between March 2008 and December 2010. The analysis of the data revealed three caveats in the current implementation of this indicator: 1.) Usually, band noise calculations are based on temporal averages over all available data at the temporal resolution desired. However, this approach will bias towards transient, single loud and nearby acoustic events rather than representing the typical ambient noise. We propose to calculate ambient noise levels on the basis of the quietest 10 s each e.g. 5-min recording. 2.) Ambient noise levels in the 125-Hz band were strongly influenced by biotic sources. We propose that definitions of noise bands suitable for monitoring of anthropogenic noise need to be tuned as to avoid region-specific biotic interference. 3.) Our recordings reveal a substantial seasonal variability of ambient noise levels (102- 115 dBrms re 1 μPa, broadband sound pressure level 5th and 95th percentile), even if selected outside biotic bands, primarily due to sea state and ice cover. This implies that detecting gradual changes in ambient noise (e.g. the frequently reported 0.3dB/a) on the basis of annual averages is rather challenging if statistical significance is required

Hydrographic influences on the summer dive behaviour of Weddell seals (Leptonychotes weddellii) in Atka Bay, Antarctica

In order to gain insights into species-level behavioural responses to the physical environment, it is necessary to obtain information from various populations and at all times of year. We analysed the influences of physical environmental parameters on the mid-summer dive behaviour of Weddell seals (Leptonychotes weddellii) from a little-known population at Atka Bay, Antarctica. Dive depth distributions followed a typical bimodal pattern also exhibited by seals from other populations and seals targeted both shallow water layers of less than 50 m and depths near the seafloor. Increased stratification of temperature layers within the water column resulted in increased forage efforts by the seals through relatively high numbers of dives to the seafloor, as well as forage effort associated with shallow dives. We interpret these behavioural responses to be due to increased water temperature stratification resulting in the concentration of prey species in particular depth layers