The role of chromatic and achromatic signals for fruit detection by birds

H. Martin Schaefer, Douglas J. Levey, Veronika Schaefer and Michael L. Avery

Behavioral Ecology, 2006, vol. 17, issue 5, 784-789

Abstract: Fruit color changes during ripening are typically viewed as an adaptation to increase signal efficacy to seed dispersers. Plants can increase signal efficacy by enhancing chromatic (wavelength related) and/or achromatic (intensity related) contrasts between fruit and background. To assess how these contrasts determine the detectability of fruit signals, we conducted 2 experiments with free-flying crows (Corvus ossifragus) under seminatural conditions in a 2025 m-super-2 aviary. Crows searched first for artificial red and black fruits and detected red fruits from a larger distance. Because artificial red fruits had higher chromatic and lower achromatic contrasts against foliage than artificial black fruits, crows apparently prioritized chromatic contrasts. Thus, the common change in fruit color from red to black during ripening does not increase signal efficacy to crows. In a second trial, crows searched for UV-reflecting and black blueberries (Vaccinum myrtillus) against backgrounds of foliage and sand. Against foliage, UV-reflecting berries had higher chromatic and achromatic contrasts than black berries, and crows detected them from a larger distance. Against sand, UV-reflecting berries had low achromatic contrasts and black berries low chromatic contrasts. Crows detected both fruit types equally, suggesting that they used chromatic contrasts to detect UV-reflecting berries and achromatic contrasts to detect black berries. Birds prioritized chromatic contrasts when searching for artificial red fruits in foliage but not when searching for blueberries on sand. We suggest that the relative importance of chromatic and achromatic contrasts is contingent on the chromatic and achromatic variance of the background. Models of signal perception can be improved by incorporating background-specific effects. Copyright 2006.

Keywords: eye model; frugivory; fruit color; perception; seed dispersal; vision (search for similar items in EconPapers)
Date: 2006
References: Add references at CitEc
Citations: View citations in EconPapers (1)

Downloads: (external link)
http://hdl.handle.net/10.1093/beheco/arl011 (application/pdf)
Access to full text is restricted to subscribers.

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:oup:beheco:v:17:y:2006:i:5:p:784-789

Ordering information: This journal article can be ordered from
https://academic.oup.com/journals

Access Statistics for this article

Behavioral Ecology is currently edited by Louise Barrett

More articles in Behavioral Ecology from International Society for Behavioral Ecology Oxford University Press, Great Clarendon Street, Oxford OX2 6DP, UK.
Bibliographic data for series maintained by Oxford University Press ().