Predator effects on terrestrial vertebrate prey: an integrated approach to responses at multiple scales

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Predators scare more prey than they kill. Killing prey obviously reduces their number but does scaring them do so as well? If so, then the predator's presence may have a far greater impact on the prey population than could be guessed from the kill rate. Minimizing the impact of introduced or invasive predators is crucial to the conservation of numerous species at risk. Dr Zanette's objectives are to, quantify the full impact of predators on terrestrial vertebrate (bird and mammal) prey, and so aid in effective conservation planning. Though recent work on insects and aquatic species shows that scaring prey can reduce their numbers faster than killing them does, it is not certain the same will be found in birds and mammals given their greater behavioural flexibility. Dr Zanette has already shown that songbirds: 1) suffer chronic stress where predators are naturally more abundant; 2) can only dramatically increase their reproductive success in response to more food, where predators are less abundant; and 3) may produce far fewer daughters than sons when exposed to predators. These and other of her discoveries have been repeatedly featured in both the international scientific, and popular, media. Dr Zanette will now take the critical next step of experimentally removing both an introduced (raccoon) and an invasive (brown-headed cowbird) predator to quantify all of the impacts on their prey, in B.C.'s southern Gulf Islands, where she conducts her research. Dr Zanette and her students will test the effects on the physiology, behaviour and reproductive output of adults; and the growth, development and survival of their young; in both song sparrows and deer mice. She and her team are singularly able to address these questions using a globally-unique, digital video system she designed that allows them to catch predators in the act. It is thanks to this system that Dr Zanette can now proceed with experimental predator removals since, like most other terrestrial vertebrate ecologists, she was previously unable to say who the principal predators were. In addition to addressing fundamental ecological processes, Dr Zanette's research will be used in planning an introduced/invasive predator mitigation program for the new Southern Gulf Islands National Park.