DOI: 10.5061/dryad.18931zcxr
title: Thermal flight performance reveals impact of warming on bumblebee foraging potential

description: The effects of environmental temperature on components of insect flight
 determine life-history traits, fitness, adaptability, and ultimately,
 organism ecosystem functional roles. Despite the crucial role of flying
 insects across landscapes, our understanding of how temperature affects
 insect flight performance remains limited. Many insect pollinators are
 considered under threat from climatic warming. Quantifying the
 relationship between temperature and behavioural performance traits allows
 us to understand where species are operating in respect to their thermal
 limits, helping predict responses to projected temperature increases
 and/or erratic weather events. Using a tethered flight mill, we quantify
 how flight performance of a widespread bumblebee, Bombus terrestris,
 varies over a temperature range (12-30oC). Given that body mass constrains
 insect mobility and behaviour, bumblebees represent a useful system to
 study temperature-mediated size-dependence of flight performance owing to
 the large intra-colony variation in worker body size they exhibit. Workers
 struggled to fly over a few hundred metres at the lowest tested
 temperature of 12oC, however flight endurance increased as temperatures
 rose, peaking around 25oC after which it declined. Our findings further
 revealed variation in flight capacity across the workforce, with larger
 workers flying further, longer, and faster than their smaller nestmates.
 Body mass was also positively related with the likelihood of flight,
 although importantly this relationship became stronger as temperatures
 cooled, such that at 12oC only the largest workers were successful fliers.
 Our study thus highlights that colony foraging success under variable
 thermal environments can be dependent on the body mass distribution of
 constituent workers, and more broadly suggests smaller-bodied insects may
 benefit disproportionately more from warming than larger-bodied ones in
 terms of flight performance. By incorporating both flight endurance and
 likelihood of flight, we calculated a simple metric termed
 ‘temperature-mediated foraging potential’ to gain a clearer understanding
 of how temperature may constrain colony foraging. Of our tested
 temperatures, 27oC supported the highest potential, indicating that for
 much of the range of this species, higher mean daily temperatures as
 forecasted under climate warming will push colonies closer to their
 thermal optimum for flight. Subsequently, warming may have positive
 implications for bumblebee foraging returns and pollination provision.
description: A raw flight data file (.dat) was produced for each flight bout,
 with each bout consisting of six workers.  Each file
 provides identifiying information for each bee flown in the bout, and then
 has a record of every circuit flown by each bee, providing information on
 the mill number, the circuit number, and the duration of the circuit in
 seconds. For reference, the circumference of each circuit is 0.848m, which
 allows the speed of each circuit and the total distacne flown by each
 bee to be calculated.  The overview spreadsheet then
 provides the flight metrics that have been calculated for each bee from
 the raw data files. Processing of the raw data files was done according to
 rules outlined in the manuscript (the R script used for this process can
 be provided upon request). The overview spreadsheet provides all necessary
 details for each bee, such as colony ID, body mass, and sucrose
 consumption data.
description: On the raw data files, lines 2 and 3 refer to the date and time
 of the trial.  The values on the subsequent lines that
 start Age/Weight/Sex actually refer to Colony ID / Temperature of Trial /
 Bee ID. For the circuit data, the 'Training
 Circuit' is just the first recorded impulse by the flight mill and is
 not timed as it will not have been a full circuit.  The
 two '_extra' data files are where the original flight data file
 was ended prematurely, so the programme was restarted to record the final
 stages of bee flight.