We examined potential benefits of group living in juvenile lake sturgeon (Acipenser fulvescens Rafinesque, 1817) and whether those benefits applied equally to associations with conspecific and allospecific individuals. In the first experiment, one focal lake sturgeon was placed with either seven size-matched conspecifics, allospecifics, or in isolation and given a 30 s air exposure. In the second experiment, one focal lake sturgeon was placed with either seven conspecifics or in isolation and was exposed to a conspecific skin homogenate as a potential alarm substance or a control of distilled water. Cortisol, norepinephrine, and epinephrine levels were measured before and after exposure in each experiment via an indwelling cannula in the caudal sinus. In the first experiment, lake sturgeon held with allospecifics and in isolation had a significantly longer norepinephrine response. Furthermore, plasma norepinephrine concentration in the focal lake sturgeon in the allospecific treatment was significantly higher than the other treatments following air exposure. In the second experiment, there was no behavioural or hormonal response to the introduction of conspecific skin homogenate, yet isolated fish had elevated baseline norepinephrine and cortisol levels. Finally, comparison of baseline levels of all three hormones between two ages of juveniles indicated an effect of age on baseline epinephrine levels. Our findings confirm the potential physiological benefit of group living in lake sturgeon and suggest an ontogenetic shift in both the behavioural response to potential stressors and the baseline hormonal levels that may influence fitness.

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Sympatric species derive benefits by attending to information conveyed by heterospecifics. Our previous finding of reduced vigilance among jackdaws and lesser kestrels residing in mixed‐species colonies suggested a reliance on interspecific communication of information regarding predatory threats. To test for interspecific communication of threat, we first determined whether jackdaw and lesser kestrel call structure varied with perceived threat. In this call production phase of our study, free‐living birds in mixed‐species colonies were presented with models representing a potential nest predator (European magpie) or with non‐threatening stimuli (wood pigeon or wooden dowel) in proximity to nests. We recorded and subsequently analysed those calls to determine if any temporal or frequency‐related call parameters differed by model type. In a second, perceptual phase of our study, we tested whether receivers perceive threat‐related variation in both conspecific and heterospecific call structure by playing back call exemplars recorded in response to the predator model or to innocuous control stimuli, to determine whether free‐living jackdaws or lesser kestrels respond differentially to playbacks of the different call types. We detected differences in vocalizations of both jackdaws and lesser kestrels relative to the model type presented, with more broadband (lesser kestrel) or noisy calls (jackdaws) in response to magpie versus innocuous model types. We also detected differential behavioural responses to call playbacks, with both jackdaws and lesser kestrels increasing vigilance and alarm calling in response to magpie‐elicited jackdaw calls, but not to other call types. Taken together, our results suggest that jackdaw, but not lesser kestrel vocalizations, communicate enhanced threat associated with European magpies as possible nest predators. This interspecific alarm communication benefits both jackdaws and lesser kestrels, and, at least in part, explains asymmetric responses of jackdaws and lesser kestrels to magpies attending mixed‐species colonies in nature.