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Chromaticity in the UV/blue range facilitates the search for achromatically background-matching prey in birds
University of Freiburg, Department of Evolutionary Biology and Animal Ecology.
Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology. Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology. Stockholm University, Faculty of Science, Department of Zoology.
University of Freiburg, Department of Evolutionary Biology and Animal Ecology.
2009 (English)In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, Vol. 364, no 1516, 511-517 p.Article in journal (Refereed) Published
Abstract [en]

A large variety of predatory species rely on their visual abilities to locate their prey. However, thesearch for prey may be hampered by prey camouflage. The most prominent example of concealingcoloration is background-matching prey coloration characterized by a strong visual resemblance ofprey to the background. Even though this principle of camouflage was recognized to efficiently workin predator avoidance a long time ago, the underlying mechanisms are not very well known. In thisstudy, we assessed whether blue tits (Cyanistes caeruleus) use chromatic cues in the search for prey.Weused two prey types that were achromatically identical but differed in chromatic properties in theUV/blue range and presented them on two achromatically identical backgrounds. The backgroundshad either the same chromatic properties as the prey items (matching combination) or differed intheir chromatic properties (mismatching combination). Our results show that birds use chromaticcues in the search for mismatching prey, whereupon chromatic contrast leads to a ‘pop-out’ of theprey item from the background. When prey was presented on a matching background, search timeswere significantly higher. Interestingly, search for more chromatic prey on the matching backgroundwas easier than search for less chromatic prey on the matching background. Our results indicate thatbirds use both achromatic and chromatic cues when searching for prey, and that the combination ofboth cues might be helpful in the search task.

Place, publisher, year, edition, pages
2009. Vol. 364, no 1516, 511-517 p.
Keyword [en]
visual search; crypsis; predation; avian vision; luminance; colour;
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-30543DOI: 10.1098/rstb.2008.0248ISI: 000262353500011OAI: oai:DiVA.org:su-30543DiVA: diva2:272844
Available from: 2009-10-18 Created: 2009-10-18 Last updated: 2009-10-19Bibliographically approved
In thesis
1. Life at stake when playing hide and seek: Concealing effects of prey colouration and visual backgrounds
Open this publication in new window or tab >>Life at stake when playing hide and seek: Concealing effects of prey colouration and visual backgrounds
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A prey animal can use different strategies to avoid becoming eaten by predators. One such widely recognised strategy is the use of body colouration to decrease the risk of becoming detected, i.e. cryptic colouration. The principles of crypsis that I have studied are background matching, disruptive colouration and distractive markings. Further, I also studied the concealing effect of the visual background habitats. I used artificial prey items and backgrounds, and blue tits (Cyanistes caeruleus) as predators, to investigate prey concealment. In Paper I, I tested if high-contrast markings in prey coloration or in the background would result in a distracting effect. I found that such markings did increase prey search time, even when the prey markings were lighter or darker than the background. In Paper II, I studied the use of chromatic cues by predators when searching for prey. The birds easily detected prey that chromatically deviated from its background. Interestingly, background-matching prey was more difficult to detect when the colour scheme had low ultraviolet and high shortwave reflectance compared to when the reflectance bands were even. In Paper III, I studied optimisation of achromatic contrast within prey colour pattern and also the effect of shape diversity of background pattern elements on prey detection. I found that all prey types were more difficult to detect on the diverse background, but the level of contrast within prey pattern did not influence search times. In Paper IV, I further investigated how a prey should optimise its patterning with respect to background matching. I found that prey with repeated pattern elements was equally hard to detect as prey with more variable pattern. However, prey with a spatially regular pattern (aligned pattern elements) was easier to detect than prey with a spatially irregular pattern. In this paper I also found that high complexity of element shapes in the background, made the search task more difficult.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2009. 34 p.
Keyword
predation; adaptive prey coloration; camouflage; concealment; crypsis; background matching; disruptive colouration; distractive markings
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-30548 (URN)978-91-7155-959-3 (ISBN)
Public defence
2009-11-20, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: AcceptedAvailable from: 2009-10-28 Created: 2009-10-18 Last updated: 2009-10-22Bibliographically approved

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