It's not just what you have, but how you use it: solar‐positional and behavioural effects on hummingbird colour appearance during courtship

Abstract

Animals exhibit a diversity of colours that can play key roles in mating interactions. However, we presently lack an understanding of the relative importance of the environment, behaviour and natural reflective properties of colourful ornaments in shaping an individual's colour appearance during mating displays. We investigated interactions among structurally based plumage, display environments and courtship shuttle displays of male Costa's hummingbirds (Calypte costae) to test how these elements may differentially contribute to colour appearance during shuttles. Male position relative to the sun was the strongest predictor of colour appearance, with shuttle behaviours and feather reflectance playing smaller roles. Furthermore, male solar orientation and shuttling behaviour (e.g. shuttle width) were repeatable among displays, whereas male colour appearance mostly was not. These results emphasise the contributions of behaviour and environment to colour-signalling and suggest that relying on reflectance measurements of colourful ornaments alone provides an incomplete picture of ecologically relevant visual phenotypes of displaying animals.

Experimental trait mismatches uncover specificity of evolutionary links between multiple signaling traits and their interactions in hummingbirds*

“…Shuttles are characterized by a male flying rapidly back and forth in front of a female while erecting his colorful plumage (Feo and Clark ; Clark et al. , , Simpson and McGraw , c). In our previous work, we tested the correlational relationships between properties of male shuttles, plumage, display environment, and their interactions to begin to understand how these signals coevolved (Simpson ).…”

“…For this study, we used previously recorded shuttle displays (from 2014–2017) and plucked feathers for each hummingbird species (Simpson ; Simpson and McGraw , c): broad‐tailed ( Selasphorus platycercus ) and black‐chinned ( Archilochus alexandri ) hummingbirds, which were studied in Arizona, and Costa's ( Calypte costae ), Calliope ( Selasphorus calliope ), and Allen's ( Selasphorus sasin ) hummingbirds, which were studied in California (see Simpson for location and permit details). Anna's hummingbirds, which were included in our previous work (Simpson ), were excluded from this study due to the fact that they do not move during their courtship display, making it difficult to mismatch their displays with other species.…”

“…Anna's hummingbirds, which were included in our previous work (Simpson ), were excluded from this study due to the fact that they do not move during their courtship display, making it difficult to mismatch their displays with other species. Captured female hummingbirds from each species were used to elicit male shuttle displays from their own species in the field (Simpson ; Simpson and McGraw , c). We presented a female in a wire‐mesh cylindrical cage with a clear plexiglass bottom (see Simpson for full description of cage set up) to males on their territories, and then we placed a high‐definition video camera (Sony HDR‐CX330) underneath the caged female, pointing up, which enabled us to film male shuttle orientations and movements in the horizontal plane (Simpson and McGraw ).…”

“…Captured female hummingbirds from each species were used to elicit male shuttle displays from their own species in the field (Simpson ; Simpson and McGraw , c). We presented a female in a wire‐mesh cylindrical cage with a clear plexiglass bottom (see Simpson for full description of cage set up) to males on their territories, and then we placed a high‐definition video camera (Sony HDR‐CX330) underneath the caged female, pointing up, which enabled us to film male shuttle orientations and movements in the horizontal plane (Simpson and McGraw ). After we filmed male shuttles, we captured the males that displayed on their territories and plucked feathers from their colorful throat patch (gorget), specifically from the area underneath their bill (Simpson and McGraw ).…”

“…We presented a female in a wire‐mesh cylindrical cage with a clear plexiglass bottom (see Simpson for full description of cage set up) to males on their territories, and then we placed a high‐definition video camera (Sony HDR‐CX330) underneath the caged female, pointing up, which enabled us to film male shuttle orientations and movements in the horizontal plane (Simpson and McGraw ). After we filmed male shuttles, we captured the males that displayed on their territories and plucked feathers from their colorful throat patch (gorget), specifically from the area underneath their bill (Simpson and McGraw ). We also quantified male plumage patch size by photographing each side of the male's head (before we plucked feathers, area in mm 2 ; Simpson and McGraw ).…”