State-dependent foraging: lactating voles adjust their foraging behavior according to the presence of a potential nest predator and season

Abstract

Parental care often produces a trade-off between meeting nutritional demands of offspring and the duties of offspring protection, especially in altricial species. Parents have to leave their young unattended for foraging trips, during which nestlings are exposed to predators. We investigated how rodent mothers of altricial young respond to risk of nest predation in their foraging decisions. We studied foraging behavior of lactating bank voles (Myodes glareolus) exposed to a nest predator, the common shrew (Sorex araneus). We conducted the experiment in summer (high resource provisioning for both species) and autumn (less food available) in 12 replicates with fully crossed factors "shrew presence" and "season." We monitored use of feeding stations near and far from the nest as measurement of foraging activity and strategic foraging behavior. Vole mothers adapted their strategies to shrew presence and optimized their foraging behavior according to seasonal constraints, resulting in an interaction of treatment and season. In summer, shrew presence reduced food intake from feeding stations, while it enhanced intake in autumn. Shrew presence decreased the number of visited feeding stations in autumn and concentrated mother's foraging efforts to fewer stations. Independent of shrew presence or season, mothers foraged more in patches further away from the nest than near the nest. Results indicate that females are not investing in nest guarding but try to avoid the accumulation of olfactory cues near the nest leading a predator to the young. Additionally, our study shows how foraging strategies and nest attendance are influenced by seasonal food provision.

Keywords: Interference; Myodes glareolus; Nest protection; Optimal foraging; Seasonality; Sorex araneus.

Fig. 1

a Seed tray exploitation by female voles in response to tray distance to nest. b Effect of the shrew treatment on the ratio of near trays/far trays. In both treatments, voles used more tray near to the nest than expected by random (reference line). Box plots show median quartiles and range of data. *p < 0.05

Fig. 2

a Effect of the season and shrew treatment on bank vole females’ mean intake of food in 24 h. b Effect of season and shrew treatment on the mean giving-up densities (GUDs) of the trays exploited by the animals. Each symbol represents a single-day average for one female from a seed tray grid around her nest. Near and far trays are pooled.*p < 0.05

Fig. 3

a Effect of shrew treatment on the number of foraging stations exploited by bank vole females. b Effect of shrew treatment on the concentration of foraging effort on the four most foraged trays (25 % would indicated an even distribution of foraging effort). Box plots show median quartiles and range of data. *p < 0.05