Behavioural and heart rate responses to stressors in two populations of Little Penguins that differ in levels of human disturbance and predation risk

Abstract

Species that are constantly exposed to disturbances, such as human disturbance or nonlethal contacts with predators or conspecifics, can experience chronic stress. Within a species range, variation in the frequency and predictability of such disturbances can lead to population differences in stress responses. Here, we investigated the stress response of Little Penguins Eudyptula minor to an introduced predator and a conspecific at two South Australian colonies that differed in habitat, conspecific density, levels of human disturbance and predation risk (high, low). We used playback experiments of Cat Felis catus or Little Penguin calls and recorded the behaviour and physiological (heart rate) response of adults in relation to playback type (Cat, Penguin) as well as habitat characteristics (habitat type, nest type, nest visibility) and number of conspecifics present. Our results showed that individuals from the high-disturbance colony (also living in a mixed habitat with fewer neighbours) exhibited higher vigilance and heart rate responses than individuals from the low-disturbance colony (living in a closed habitat with a high number of neighbours). Our results highlight that guidelines for managing penguin species cannot be generalized across populations and need to be colony-specific.

Noisy neighbours: effects of construction noises on nesting seabirds

“…Each track began with 45 min of silence to allow individuals to recover from the deployment of the equipment. Both Larcombe (2016) and Schaefer and Colombelli-Négrel (2021) showed that little penguin heart-rate values returned to baseline levels within half an hour of deployment; hence, we are confident that this interval was sufficient. The 45 min of silence included periodic short bursts (of 1 s) of environmental noises (noises caused by the wind and the ocean and obtained from previous recordings, played at ~65 dB at 1 m every 5 min) to prevent the iPod from shutting down.…”

“…For each tested nest, the sex of the adult penguin present in the nest was confirmed using photographic identification, as previously described for little penguins (Colombelli-Négrel and Smale 2018; Wasiak 2020; Schaefer and Colombelli-Négrel 2021); the fact that the bird was incubating eggs (and not sitting on young chicks) was also established. A dummy egg was then added to the clutch without removing any of the natural eggs to record their physiological response (heart rate) following Schaefer and Colombelli-Négrel (2021). The dummy egg contained an internal omnidirectional lavalier condenser microphone (WL183, Shure Inc., USA) connected to either a Zoom H4n (Zoom North America, USA) or a Tascam DR-05 (TEAC Corporation, USA) as described in Schaefer and Colombelli-Négrel (2021).…”

“…A dummy egg was then added to the clutch without removing any of the natural eggs to record their physiological response (heart rate) following Schaefer and Colombelli-Négrel (2021). The dummy egg contained an internal omnidirectional lavalier condenser microphone (WL183, Shure Inc., USA) connected to either a Zoom H4n (Zoom North America, USA) or a Tascam DR-05 (TEAC Corporation, USA) as described in Schaefer and Colombelli-Négrel (2021). Once the dummy egg was placed, a Sony AS20 Action Camera (Sony Corporation, Australia) was set up directly at the entrance of the nest to record the adult behavioural responses.…”

“…On the basis of previous literature in birds and their response to anthropogenic noises (Brown 1990;Melanie 2004;Hughes et al 2008;Humphries and Huettmann 2014;Watson et al 2014;Derose-Wilson et al 2015;Soldatini et al 2015;Buxton et al 2017aBuxton et al , 2017bFranks 2017;Bevan et al 2018), we hypothesised that individuals would display higher vigilance and distressed behaviours in response to the construction noises than to the rainfall noises. We also hypothesised that sexes will not differ in their behavioural and physiological response on the basis of previous studies in little penguins (Carroll et al 2016;Schaefer and Colombelli-Négrel 2021). Finally, we hypothesised that breeding success will be lower for the nests exposed to the noise experiments than for those that were not (Klomp et al 1991, Weerheim et al 2003Giling et al 2008).…”

The social transmission of stress in animal collectives

“…Repeated exposure to acute stressors can change physiological set points and lower the threshold at which physiological mediators start to act pathologically (see homeostatic overload [4]), paralleling effects of chronic stress and making individuals more vulnerable to other prospective stressors [19]. Repeated capture stress makes little penguins ( Eudyptula minor ) react more strongly to subsequent stressors [20] and penguins from a high-disturbance colony give stronger heart rate responses to predator cues [21]. Further, evidence is accumulating that not only the ability to trigger an appropriate stress response is an essential survival mechanism, but also the ability to switch off the stress response when the threat has passed (e.g.…”