Anthropogenic noise alters dwarf mongoose responses to heterospecific alarm calls

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. (0) 960028260, no fax number Statement of authorshipAll authors contributed to the conception and design of the study; AM and AB collected the data; AM and AB analysed the data with advice from JMK and ANR; ANR and AM wrote the first draft of the manuscript, and all authors contributed significantly to revisions. 2Anthropogenic noise is an evolutionarily novel and widespread pollutant in both terrestrial and aquatic habitats. Despite increasing evidence that the additional noise generated by human activities can affect vocal communication, the majority of research has focused on the use of conspecific acoustic information, especially sexual signals.Many animals are known to eavesdrop on the alarm calls produced by other species, enhancing their likelihood of avoiding predation, but how this use of heterospecific information is affected by anthropogenic noise has received little empirical attention.Here, we use two field-based playback experiments on a habituated wild population of dwarf mongooses (Helogale parvula) to determine how anthropogenic noise influences the response of foragers to heterospecific alarm calls. We begin by demonstrating that dwarf mongooses respond appropriately to the alarm calls of sympatric chacma baboons (Papio ursinus) and tree squirrels (Paraxerus cepapi); fleeing only to the latter.We then show that mongoose foragers are less likely to exhibit this flee response to tree squirrel alarm calls during road-noise playback compared to ambient-sound playback.One explanation for the change in response is that noise-induced distraction or stress result in maladaptive behaviour. However, further analysis revealed that road-noise playback results in increased vigilance and that mongooses showing the greatest vigilance increase are those that do not subsequently exhibit a flee response to the alarm call. These individuals may therefore be acting appropriately: if the greater gathering of personal information indicates the absence of an actual predator despite an alarm call, the need to undertake costly fleeing behaviour can be avoided. Either way, our study indicates the potential for anthropogenic noise to interfere with the use of acoustic information from other species, and suggests the importance of considering how heterospecific networks are affected by this global pollutant.Capsule: Anthropogenic noise reduces the likelihood of fleeing to a heterospecific alarm call.3

Why does noise reduce response to alarm calls? Experimental assessment of masking, distraction and greater vigilance in wild birds

“…Although the patterns of fleeing in Experiment 2 could in principle arise from increased vigilance during Overlapping noise, there was no evidence for this mechanism. Specifically, if playback of Overlapping noise prompted greater vigilance, then birds might not respond to the alarm calls because they already knew that there was no predator nearby, not because the calls were inaudible (Morris‐Drake et al, ). Contrary to this explanation, blind‐scoring of video revealed that there was no difference in the proportion of time birds had their head up during Overlapping and Non‐overlapping noise immediately before the alarm call.…”

“…A similar logic has been used to discriminate the effects of masking and distraction on the foraging performance of bats in the presence of noise (Luo et al, ), and female frogs responding to male mating calls (Senzaki et al, ). A reduced response specifically during Overlapping noise could, however, also arise if birds were more vigilant during Overlapping noise, and so were aware that no predator was nearby and were therefore less likely to flee (Morris‐Drake et al, ). We therefore quantified vigilance during the background noise immediately before the alarm playback to test whether differences in vigilance could explain observed responses.…”

“…Anthropogenic noise from resource extraction, industry and transportation is now pervasive in both aquatic and terrestrial ecosystems around the world, and can disturb wildlife and affect the physiology, behaviour and fitness of species in diverse taxa (Barber, Crooks, & Fristrup, ; Cox, Brennan, Gerwing, Dudas, & Juanes, ; Kunc, McLaughlin, & Schmidt, ; Morley, Jones, & Radford, ; Shannon et al, ; Slabbekoorn et al, ). The most commonly studied behavioural impact of anthropogenic noise is that on acoustic communication, where the empirical focus has been on effects rather than mechanisms (Chan, Giraldo‐Perez, Smith, & Blumstein, ; Cox et al, ; Francis & Barber, ; Morris‐Drake, Bracken, Kern, & Radford, ; Radford, Kerridge, & Simpson, ; Shannon et al, ; Slabbekoorn & den Boer‐Visser, ). However, understanding mechanisms is important because it can help predict effects of noise and suggest methods to ameliorate these effects (Francis & Barber, ).…”

“…Signallers may change their singing behaviour—for instance, the time of day that they vocalize and acoustic characteristics of songs—as a consequence of noise, and receiver responses to song can be compromised in noisy conditions (Brumm & Zollinger, ; Halfwerk et al, ; Moseley et al, ; Read et al, ; Slabbekoorn & den Boer‐Visser, ). Far less work has considered how noise affects other types of acoustic communication, including anti‐predator signalling (Kern & Radford, ; Lowry, Lill, & Wong, ; Morris‐Drake et al, ; Potvin, Mulder, & Parris, ). Compromised response to signals about predators is likely to reduce survival, so it is important to understand constraints imposed by noise (Templeton, Zollinger, & Brumm, ).…”

“…Similarly, great tits ( Parus major ) usually approached a loudspeaker playing conspecific mobbing calls during simultaneous playback of low‐amplitude but not high‐amplitude traffic noise (Templeton et al, ). Responses to heterospecific alarm calls can be similarly compromised: dwarf mongooses ( Helogale parvula ) were less likely to flee to tree squirrel ( Paraxerus cepapi ) alarm calls during traffic‐noise playback compared to ambient‐sound playback (Morris‐Drake et al, ), and northern cardinals ( Cardinalis cardinalis ) failed to respond to tufted titmice ( Baeolophus bicolor ) alarm calls in noisier locations near roads (Grade & Sieving, ).…”