Bejder Lars

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Bejder
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Lars
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  • Article
    Estimated communication range and energetic cost of bottlenose dolphin whistles in a tropical habitat
    (Acoustical Society of America, 2012-01) Jensen, Frants H. ; Beedholm, Kristian ; Wahlberg, Magnus ; Bejder, Lars ; Madsen, Peter T.
    Bottlenose dolphins (Tursiops sp.) depend on frequency-modulated whistles for many aspects of their social behavior, including group cohesion and recognition of familiar individuals. Vocalization amplitude and frequency influences communication range and may be shaped by many ecological and physiological factors including energetic costs. Here, a calibrated GPS-synchronized hydrophone array was used to record the whistles of bottlenose dolphins in a tropical shallow-water environment with high ambient noise levels. Acoustic localization techniques were used to estimate the source levels and energy content of individual whistles. Bottlenose dolphins produced whistles with mean source levels of 146.7±6.2 dB re. 1 μPa(RMS). These were lower than source levels estimated for a population inhabiting the quieter Moray Firth, indicating that dolphins do not necessarily compensate for the high noise levels found in noisy tropical habitats by increasing their source level. Combined with measured transmission loss and noise levels, these source levels provided estimated median communication ranges of 750 m and maximum communication ranges up to 5740 m. Whistles contained less than 17 mJ of acoustic energy, showing that the energetic cost of whistling is small compared to the high metabolic rate of these aquatic mammals, and unlikely to limit the vocal activity of toothed whales.
  • Article
    Population comparison of right whale body condition reveals poor state of the North Atlantic right whale
    (Inter Research, 2020-04-23) Christiansen, Fredrik ; Dawson, Stephen M. ; Durban, John W. ; Fearnbach, Holly ; Miller, Carolyn A. ; Bejder, Lars ; Uhart, Marcela ; Sironi, Mariano ; Corkeron, Peter ; Rayment, William ; Leunissen, Eva ; Haria, Eashani ; Ward, Rhianne ; Warick, Hunter A. ; Kerr, Iain ; Lynn, Morgan S. ; Pettis, Heather M. ; Moore, Michael J.
    The North Atlantic right whale Eubalaena glacialis (NARW), currently numbering <410 individuals, is on a trajectory to extinction. Although direct mortality from ship strikes and fishing gear entanglements remain the major threats to the population, reproductive failure, resulting from poor body condition and sublethal chronic entanglement stress, is believed to play a crucial role in the population decline. Using photogrammetry from unmanned aerial vehicles, we conducted the largest population assessment of right whale body condition to date, to determine if the condition of NARWs was poorer than 3 seemingly healthy (i.e. growing) populations of southern right whales E. australis (SRWs) in Argentina, Australia and New Zealand. We found that NARW juveniles, adults and lactating females all had lower body condition scores compared to the SRW populations. While some of the difference could be the result of genetic isolation and adaptations to local environmental conditions, the magnitude suggests that NARWs are in poor condition, which could be suppressing their growth, survival, age of sexual maturation and calving rates. NARW calves were found to be in good condition. Their body length, however, was strongly determined by the body condition of their mothers, suggesting that the poor condition of lactating NARW females may cause a reduction in calf growth rates. This could potentially lead to a reduction in calf survival or an increase in female calving intervals. Hence, the poor body condition of individuals within the NARW population is of major concern for its future viability.
  • Article
    Vessel noise effects on delphinid communication
    (Inter-Research, 2009-12-03) Jensen, Frants H. ; Bejder, Lars ; Wahlberg, Magnus ; Aguilar De Soto, Natacha ; Johnson, Mark P. ; Madsen, Peter T.
    Increasing numbers and speeds of vessels in areas with populations of cetaceans may have the cumulative effect of reducing habitat quality by increasing the underwater noise level. Here, we first use digital acoustic tags to demonstrate that free-ranging delphinids in a coastal deep-water habitat are subjected to varying and occasionally intense levels of vessel noise. Vessel noise and sound propagation measurements from a shallow-water habitat are then used to model the potential impact of high sound levels from small vessels on delphinid communication in both shallow and deep habitats, with bottlenose dolphins Tursiops sp. and short-finned pilot whales Globicephala macrorhynchus as model organisms. We find that small vessels travelling at 5 knots in shallow water can reduce the communication range of bottlenose dolphins within 50 m by 26%. Pilot whales in a quieter deep-water habitat could suffer a reduction in their communication range of 58% caused by a vessel at similar range and speed. Increased cavitation noise at higher speeds drastically increases the impact on the communication range. Gear shifts generate high-level transient sounds (peak– peak source levels of up to 200 dB re 1 µPa) that may be audible over many kilometres and may disturb close-range animals. We conclude that noise from small vessels can significantly mask acoustically mediated communication in delphinids and contribute to the documented negative impacts on animal fitness.
  • Article
    Impact assessment research : use and misuse of habituation, sensitisation and tolerance in describing wildlife responses to anthropogenic stimuli
    (Inter-Research, 2009-12-03) Bejder, Lars ; Samuels, Amy ; Whitehead, Hal ; Finn, H. ; Allen, S.
    Studies on the effects of anthropogenic activity on wildlife aim to provide a sound scientific basis for management. However, misinterpretation of the theoretical basis for these studies can jeopardise this objective and lead to management outcomes that are detrimental to the wildlife they are intended to protect. Misapplication of the terms ‘habituation’, ‘sensitisation’ and ‘tolerance’ in impact studies, for example, can lead to fundamental misinterpretations of research findings. Habituation is often used incorrectly to refer to any form of moderation in wildlife response to human disturbance, rather than to describe a progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial. This misinterpretation, when coupled with the widely held assumption that habituation has a positive or neutral outcome for animals, can lead to inappropriate decisions about the threats human interactions pose to wildlife. We review the conceptual framework for the use of habituation, sensitisation and tolerance, and provide a set of principles for their appropriate application in studies of behavioural responses to anthropogenic stimuli. We describe how cases of presumed habituation or sensitisation may actually represent differences in the tolerance levels of wildlife to anthropogenic activity. This distinction is vital because impact studies must address (1) the various mechanisms by which differing tolerance levels can occur; and (2) the range of explanations for habituation- and sensitisation-type responses. We show that only one mechanism leads to true behavioural habituation (or sensitisation), while a range of mechanisms can lead to changes in tolerance.