Male bumblebees adapt foraging to environmental conditions to sustain mate-seeking efforts

Abstract

Male bees navigate complex trade-offs between energy acquisition and reproductive signalling, yet their movement strategies remain understudied. Unlike workers that optimise foraging to support the colony, males forage independently to collect nectar and deposit sex pheromones on selected plants. Using high-resolution 3D tracking in an indoor flight cage, we investigated how the spatial arrangement of nectar and scent-marking sites, along with nectar availability, influence male movement patterns. We manipulated the distribution of feeders (artificial flowers) and scent-marking locations (branches), and varied nectar delivery rates, to assess effects on foraging, scent-marking, and patrolling. Males responded strongly to spatial structure: in clumped arrays with evenly spaced resources, movements between consecutive visits were shorter and more localised, while in dispersed arrays with irregular spacing, transitions were longer and more variable. The combination of dispersed spacing and low nectar availability imposed the highest foraging demands, resulting in fewer feeding events and reduced total feeding time. Despite these increased costs, males maintained consistent investment in reproductive behaviours, suggesting a prioritisation of mate-seeking over energy gain. Rather than reducing signalling, males adjusted their foraging strategy--favouring fewer but prolonged feeding bouts when nectar availability allowed. These findings reveal a unidirectional behavioural adjustment, in which foraging is modulated to sustain reproductive effort, and show how spatial resource structure and nectar availability together shape movement decisions in male pollinators. LAY SUMMARYMale bumblebees keep searching for mates even when food is scarce, adjusting how they forage to conserve energy. Using 3D tracking in a controlled environment, we found that males reduce foraging effort but maintain reproductive behaviours. This shows how animals balance survival and reproduction in changing environments, offering new insights into pollinator behaviour and resilience.