Abstract
Insect pollinators such as bumblebees play a vital role in many ecosystems, so it is important to understand their foraging movements on a landscape scale. We used harmonic radar to record the natural foraging behaviour of Bombus terrestris audax workers over their entire foraging career. Every flight ever made outside the nest by four foragers was recorded. Our data reveal where the bees flew and how their behaviour changed with experience, at an unprecedented level of detail. We identified how each bee’s flights fit into two categories—which we named exploration and exploitation flights—examining the differences between the two types of flight and how their occurrence changed over the course of the bees’ foraging careers. Exploitation of learned resources takes place during efficient, straight trips, usually to a single foraging location, and is seldom combined with exploration of other areas. Exploration of the landscape typically occurs in the first few flights made by each bee, but our data show that further exploration flights can be made throughout the bee’s foraging career. Bees showed striking levels of variation in how they explored their environment, their fidelity to particular patches, ratio of exploration to exploitation, duration and frequency of their foraging bouts. One bee developed a straight route to a forage patch within four flights and followed this route exclusively for six days before abandoning it entirely for a closer location; this second location had not been visited since her first exploratory flight nine days prior. Another bee made only rare exploitation flights and continued to explore widely throughout its life; two other bees showed more frequent switches between exploration and exploitation. Our data shed light on the way bumblebees balance exploration of the environment with exploitation of resources and reveal extreme levels of variation between individuals.
Highlights
Recent advances in animal-tracking technology have brought within reach the goal of tracking every movement of individual animals over their entire lifetimes [1]
Dates Total days Track days Total flights Explorations preceding 1st exploitation flight Total number of exploitation flights Proportion of flights that were exploitation Flights/day (Mean ± sd) Flight duration Time in flight Time between flights Flight distance (m, Mean ± sd) Max distance from nest (m, Mean ± sd) Number of nights bee did not return to nest Number of flights during which we made observations Number of thistle patches bee observed in Number of marked thistles
We have gathered a wealth of data on the movements of individual bees and shed light on several important aspects of their foraging behaviour, including quantifying the relative frequency of flights fitting our definitions of exploration and exploitation flights, examining when forage sites are first discovered and illuminating the high degree of inter-individual variation in foraging behaviour
Summary
Recent advances in animal-tracking technology have brought within reach the goal of tracking every movement of individual animals over their entire lifetimes [1]. The potential of such lifelong tracks to advance our understanding of animal behaviour has been compared to that of the PLOS ONE | DOI:10.1371/journal.pone.0160333. We are able to tell the ‘life stories’ of our focal bees, providing fresh insights into the way they explore their environment and exploit the floral resources they find there, and answering a number of questions that can only be addressed by continuous, life-long monitoring: How do the flight characteristics of individual bees change over a lifetime? We are able to tell the ‘life stories’ of our focal bees, providing fresh insights into the way they explore their environment and exploit the floral resources they find there, and answering a number of questions that can only be addressed by continuous, life-long monitoring: How do the flight characteristics of individual bees change over a lifetime? Do flights transform gradually from exploration of the environment to focussed foraging trips or switch suddenly? Does exploration occur only at the start of a foraging career or does it continue throughout a bee’s life? Do individuals switch fluidly between multiple foraging sites or specialise on a single one? And do individual bees show similar patterns over their lives or do different bees employ different foraging strategies? Globally, pollinator species are in decline [6,7,8], so a deeper understanding of their movements and foraging behaviour is needed for understanding population dynamics and informing conservation efforts [9]
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