A study of the species-confidence hypothesis with Spiny-cheeked Honeyeaters (Acanthagenys rufogularis)

Abstract

The species-confidence hypothesis states that birds are attracted to colours found on their own body and are repelled by colours not found on their body. Previous studies have examined this hypothesis by measuring the distance at which birds took flight in response to humans approaching them while wearing different-coloured clothes. One study found that birds without red or orange on their bodies had longer flight-initiation distances when an orange vest was worn, while birds with those colours on their bodies were not affected. We evaluated the species-confidence hypothesis by approaching Spiny-cheeked Honeyeaters (Acanthagenys rufogularis) while wearing four different-coloured T-shirts and noted their flight-initiation distance. We predicted that birds would allow us to approach closer if we were wearing a colour found on their body. Unlike previous studies, we accounted for the fact that different colours are differentially detectable in the field because detectability alone may influence flight-initiation distance (i.e. bright colours are more detectable simply because they are bright). Two shirts were highly detectable (red and yellow) and two were relatively cryptic (tan and olive). Specifically, Spiny-cheeked Honeyeaters were found to have the longest flight-initiation distances when approached by a person wearing a yellow T-shirt (a colour not found on the bird), and the shortest flight-initiation distances when approached by a person wearing a red T-shirt (a colour found on the bird). The species-confidence hypothesis may account for variable flight-initiation distances.