Fruit selection in the olive thrush: the importance of colour

Abstract

Free-living olive thrushes Turdus o/ivaceus were offered a choice of wild olive Olea africana fruit of four colours, representing four ripeness categories. The thrushes ate mostly black fruit (ripest), followed by maroon (ripe) and olivecoloured (partially ripe) fruit. When riper fruit was unavailable, the thrushes selected more maroon or olive-coloured fruit. Green fruit (unripe) were never eaten, even when these were the only ones available. When offered pieces of dyed pear Pyrus communis, the thrushes preferentially selected orange pieces, followed by red and black pieces. Green pieces were never eaten. The results indicated that olive thrushes selected fruit on the basis of fruit colour, and that colour preferences differed between the two types of fruit offered.

Inter‐specific and intra‐specific variability in fruit color preference in two species of Turdus

“…The data available, however, do not allow us to conclude that there is a clear and general preference for red fruits. Although in some cases red was preferred (McPherson 1988;Puckey et al 1996;Traveset & Willson 1998;Giles & Lill 1999;Alves-Costa & Lopes 2001), there are other cases where different colors were preferred over red (Murray et al 1993;Willson 1994;Sanders et al 1997;Schmidt 2002;Stanley et al 2002;Galetti et al 2003;Honkavaara et al 2004). These results suggest that color preferences are not an invariant trait in frugivorous birds, but rather show ample variation among species.…”

“…Third, the artificial green fruits used showed higher reflectance than all other colors; hence, they were (relative to these) more conspicuous than would be expected under natural conditions. Instead, avoidance of unripe fruits seems to be a more likely reason for the avoidance of green color by Redwings and Eurasian Blackbirds (McPherson 1988;Sanders et al 1997). The use of visual cues for assessing fruit quality has been previously reported (Traveset & Willson 1995;Stanley et al 2002), although it can be strongly contextdependent (e.g.…”

“…Both species consistently avoided green fruits, and this was a pervasive trend in all trials and for all individuals from both species. Although green has often been left out of color-preference experiments, avoidance of green fruits seems to be a common pattern among fruit-eating birds (Knight & Siegfried 1983;McPherson 1988;Willson & Comet 1993;Sanders et al 1997; but see . Several authors have proposed that green color is less consumed due to its low conspicuousness against the background , although this hypothesis awaits proper experimental testing, and some results seem to contradict it: for example, in a sample of 43 species from southern Venezuela, the only green fruit showed a higher contrast than the majority of fruits (Schmidt 2002).…”

“…Several authors have proposed that green color is less consumed due to its low conspicuousness against the background , although this hypothesis awaits proper experimental testing, and some results seem to contradict it: for example, in a sample of 43 species from southern Venezuela, the only green fruit showed a higher contrast than the majority of fruits (Schmidt 2002). Other authors have proposed that birds might be using green as a cue to detect unripe fruits (McPherson 1988;Sanders et al 1997). In the present study, conspicuousness was not a likely determinant of (green) fruit-color preferences.…”

“…claimed that improving our knowledge on disperser preferences is a priority if we are to understand the forces driving the evolution of color in fleshy fruits. Studies on fruit color preferences of dispersers are still scarce and have involved a very small number of species, mainly birds (McPherson 1988;Murray et al 1993;Willson & Comet 1993;Puckey et al 1996;Sanders et al 1997;Giles & Lill 1999;Siitari et al 1999;Alves-Costa & Lopes 2001;Schmidt 2002;Stanley et al 2002;Honkavaara et al 2004). Moreover, some of these studies present important statistical and procedural problems (e.g.…”