Date Published: June 19, 2019
Publisher: Public Library of Science
Author(s): Mª Carmen Hernández, Álvaro Navarro-Castilla, Isabel Barja, Ofer Ovadia.
Animals making foraging decisions must balance the energy gained, the time invested, and the influence of key environmental factors. In our work, we examined the effect of predation risk cues and experience on feeding efforts when a novel food resource was made available. To achieve this, we live-trapped wood mouse Apodemus sylvaticus in Monte de Valdelatas (Madrid), where 80 Sherman traps were set in four plots. Traps were subjected to two food-access difficulties in treatments consisting of three consecutive nights: open plastic bottles (easy) and closed bottles (difficult), both using corn as bait. To simulate predation risk, we set fox faeces in half of the traps in each plot. We also considered moonlight (medium/low) as an indirect predation risk cue. We analysed whether bottles had been bitten by mice and the gnawed area of each bottle was measured. Our results indicated that food access difficulty, experience, and predation risk determined mice feeding decisions and efforts. The ability of mice to adapt feeding effort when a new food source is available was demonstrated because a higher proportion of closed bottles exhibited bite marks and the gnawed area was bigger. Moreover, mouse experience was determinant in the use of this new resource since recaptured mice gnawed broader orifices in the bottles and the gnawed area increased each time an individual was recaptured. Additionally, direct predation risk cues prompted mice to bite the bottles whereas the effect of different moon phases varied among the food access treatments. This study provides direct evidence of formidable efficacy of wild mice to exploit a new nutrient resource while considering crucial environmental factors that shape the decision-making procedure.
According to the optimal foraging theory, choices made by animals when foraging and selecting food aim to maximise fitness [1, 2, 3]. The variable food availability challenges animals to evaluate the trade-offs between nutrient demands and the energetic cost of foraging, thereby selecting the type of food with the maximum net benefit [1, 2]. These changeable environmental conditions have led to the development of a wide array of adaptations to efficiently exploit and utilise heterogeneous food resources in several life forms [4, 5]. The mechanisms which underly feeding choices are rather diverse, with both endogenous and environmental factors involved in the decision process [6, 7]. It is known that animals possess the ability to learn about the characteristics of the items in their diet and that feeding choices are dependent upon experience [7, 8]. Moreover, gathering information about food availability in a novel environment comes at a cost, because exploratory behaviours increase exposure to predation and divert time and energy from other fitness-enhancing activities (i.e., foraging, reproduction, predation risk assessment, etc.) . However, those individuals that early allocate more energy to acquire information can learn the true value of the environment more quickly, which can lead to higher fitness gains due to a more efficient exploitation . In this manner, learning can provide animals with the key to quickly adapt to this ever-changing environment by displaying novel feeding strategies when new food sources are present.