J Comp Physiol A (1995) 177:1 19 Springer-Verlag 1995 K. Lunau E. J. Maier Innate colour preferences of flower visitors Accepted: 16 January 1995 Abstract Freshly emerged flower visitors exhibit col- our preferences prior to individual experience with flowers. The understanding of innate colour preferences in flower visitors requires a detailed analysis, as, on the one hand, colour is a multiple-signal stimulus, and, on the other hand, flower visits include a sequence of behavioural reactions each of which can be driven by a preferential behaviour. Behavioural reactions, such as the distant approach, the close-range orienta- tion, the landing, and the extension of mouthparts can be triggered by colour stimuli. The physiological limitations of spectral sensitivity, the neuro-sensory filters, and the animals' different abilities to make use of visual information such as brightness perception, wavelength-specific behaviour and colour vision shape colour preferences. Besides these receiver- based factors, there are restrictions of flower coloura- tion due to sender-based factors such as the absorption properties of floral pigments and the dual function of flower colours triggering both innate and learned be- haviour. Recordings of the spectral reflection of col- oured objects, which trigger innate colour preferences, provide an objective measure of the colour stimuli. Weighting the spectral reflection of coloured objects by the spectral composition of the ambient light and the spectral sensitivity of the flower visitors' photorecep- tors allows the calculation of the effective stimuli. Per- ceptual dimensions are known for only a few taxa of flower visitors. Key words Colour preference Flower colouration Flower visitation Visual signals Innate behaviour K. Lunau (12N) E. J. Maier Institut fiir Zoologie der Universit~it Regensburg, Universitiitsstrasse 31, D-93040 Regensburg, Germany Introduction The signalling function of flower colours and floral colour patterns to flower visitors was firstly described by Sprengel (1793) in his monograph "The Discovered Mystery of Nature in the Construction and Fertiliza- tion of Blossoms". Flowering syndrome terminology dates back to the classification established by Delpino (1868-75). Non-related plant species with convergently evolved particular morphological and signalling traits adapted to the flower visitors were grouped together. Nowadays it is generally accepted that the display of colourful flowers provides effective releasers which trig- ger behavioural reactions in flower visitors (Daumer 1958; von Frisch 1965; Kevan 1978; Chittka and Menzel 1992; Menzel and Shmida 1993). Other visual, olfactory and tactile cues can aid the orientation at flowers (Butler 1951; Bolwig 1954; Cameron 1981; Dobson et al. 1990; Kevan and Lane 1985). Preference behaviour of flower visitors towards floral colours may develop for different reasons. Innate colour preferences represent phylogenetic adaptations of species operating prior to individual experience with flowers. They address themselves towards food signals, and are independent of the actual reward conditions. Learned colour preferences represent temporary spe- cializations of individuals. They are dependent on the learning abilities of these animals and on the reward conditions of food sources. Much more is known today about learned colour preferences than about innate colour preferences. We want to concentrate on this somewhat neglected topic. It is not surprising to find that flower-visiting animals have an innate preference for flowers that are impor- tant to them. However, colour is a multiple-signal stimulus. Individual aspects of the same colour (inten- sity, predominant wavelength, spectral purity, colour contrast) can be used in different behavioural contexts, such as initial flower detection and flower constant