1105 INTRODUCTION Bumblebees perform learning flights to acquire visual information about the arrangement of landmarks around the nest that can help guide their later return flights. They control flight direction and body orientation in relation to both nest-based coordinates (Philippides et al., 2013) and compass bearings (Hempel de Ibarra et al., 2009). Bees thus obtain similar views when facing in directions close to the nest in particular segments of the stereotyped loop and zigzag motifs that characterize their learning and return flights (Philippides et al., 2013). This dual control of flight can be seen in plots of the frequency distributions of body orientation and flight direction during these motifs. Body orientation has a more prominent and narrower peak than flight direction in both nest- and compass-based coordinates (Fig. 1). When plotted relative to the nest, the mode of the distribution is in the direction of the nest (Fig. 1A). Flight direction is less focused. There is a peak in the direction of the nest during zigzags and peaks either side of the nest during loops (Fig. 1B). The mode of body orientation plotted in compass coordinates is just west of north (Fig. 1C), whereas flight directions are broadly distributed in loops and zigzags (Fig. 1D). To face towards the nest while flying over a wider range of flight directions, bees adjust the angle between flight direction and body orientation (Philippides et al., 2013). The results presented here allow us to explain the similar concentration of viewing directions relative to compass bearings. The bee’s direction of travel in particular surroundings may in principle be controlled by the surrounding panorama (von Frisch and Lindauer, 1954; von Frisch, 1967; Towne and Moscrip, 2008; Graham and Cheng, 2009), or by celestial compass information (Wehner and Rossel, 1985; Riley et al., 2005), or by both reference frames (Dyer, 1987; Towne and Moscrip, 2008). In familiar surroundings, the distant panorama and compass information usually provide concordant guidance cues. If the two are put in conflict, cues from the panorama can overwhelm compass information and control the insect’s direction of movement (von Frisch, 1967; Graham and Cheng, 2009). In unfamiliar surroundings, or when flying insects are tethered, guidance can be by compass cues alone (Mouritsen and Frost, 2002). Bumblebee learning flights provide an interesting case. Because body orientation is tied more closely to the position of the nest than is flight direction (Fig. 1A,B), the relation between body orientation and flight direction varies. Were body orientation to be fixed relative to flight direction, it would be straightforward to maintain a set flight direction by keeping features of the surrounding panorama in fixed retinal positions. It is more complicated if, as here, body orientation varies relative to flight direction. The image of the panorama on the retina is not then an easy cue to use for controlling flight direction. How do bees control their flight direction under these circumstances? We approach this question by analysing how straight segments of flight are maintained and find that the direction of straight segments is probably set by compass cues. We then show that bees have preferred compass directions of flight associated with different phases of their nest-based loops and zigzags, and examine how nest- SUMMARY Bumblebees tend to face their nest over a limited range of compass directions when learning the nestʼs location on departure and finding it on their approach after foraging. They thus obtain similar views of the nest and its surroundings on their learning and return flights. How do bees coordinate their flights relative to nest-based and compass-based reference frames to get such similar views? We show, first, that learning and return flights contain straight segments that are directed along particular compass bearings, which are independent of the orientation of a beeʼs body. Bees are thus free within limits to adjust their viewing direction relative to the nest, without disturbing flight direction. Second, we examine the coordination of nest-based and compass- based control during likely information gathering segments of these flights: loops during learning flights and zigzags on return flights. We find that bees tend to start a loop or zigzag when flying within a restricted range of compass directions and to fly towards the nest and face it after a fixed change in compass direction, without continuous interactions between their nest-based and compass-based directions of flight. A preferred trajectory of compass-based flight over the course of a motif, combined with the tendency of the bees to keep their body oriented towards the nest automatically narrows the range of compass directions over which bees view the nest. Additionally, the absence of interactions between the two reference frames allows loops and zigzags to have a stereotyped form that can generate informative visual feedback. Key words: compass-based flight, nest-based flight, coordinating reference frame, insect navigation, learning flight. Received 11 October 2012; Accepted 20 November 2012 The Journal of Experimental Biology 216, 1105-1113 © 2013. Published by The Company of Biologists Ltd doi:10.1242/jeb.081463 RESEARCH ARTICLE Coordinating compass-based and nest-based flight directions during bumblebee learning and return flights Thomas S. Collett 1, *, Natalie Hempel de Ibarra 1,† , Olena Riabinina 2,‡ and Andrew Philippides 2, * 1 Department of Informatics and 2 School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK *Authors for correspondence (t.s.collett@sussex.ac.uk; andrewop@sussex.ac.uk) † Present address: Psychology, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QG, UK ‡ Present address: Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA THE฀JOURNAL฀OF฀EXPERIMENTAL฀BIOLOGY