Multispectral Coloration at the Burke Museum
Hummingbird sight has only been consistently studied in the last few years. Humans can see the visible spectrum of light, but that’snot all that exists. The sun produces ultraviolet light rays and there are also infrared light rays. We are aware that these ultravioletrays exist (have you ever had a sunburn?), but we as humans cannot detect them visually. Recent work (Stoddard et al., 2020) tells us that hummingbirds can see visible colors with three cones (like humans), but they also have a fourth cone that allows them to differentiate ultraviolet light as well!
A key part of our work at the Behavioral Ecophysics Lab is to investigate the role of coloration in sexual selection and behavior. One behavior that intrigues us, specifically, is a behavior we’ve seen in videos where a species of hummingbird (Pterophanes cyanopterus; Sapphirewing Hummingbirds) take a pause mid-flap, exposing the underside of their wing for an slightly longer duration than a typical flap. When they do this, a small patch of iridescent color is visible on the underside of the wing, and for a slightly longer period due to this pause. We want to know why they pause and what might be special about the colors on these patches– both for the bird who is flapping to show it off and also for the bird observing these color patches.
Taking these two factors into account we are asking the question: if we know coloration is used for communication, we know iridescence helps with this communication, and we know light interacts with color and iridescent patches– what does all this look like to another hummingbird?
Using the world’s largest spread wing collection that is at our fingertips at the Burke Museum at the University of Washington, we can begin to visualize what these patches of iridescent might look like. We are doing this using a specialized camera that allows a full spectrum of light to be collected, including UV and IR light rather than just the visible light that most cameras capture.
With this camera we have two lenses, one that only allows light on the visible spectrum (think of this filter as the “human eye”) and one that only allows in ultraviolet light (think of this as what the hummingbird has extra, the “fourth cone filter”). We will take photos with both of these lenses to compare the characteristics between the two. We can’t do this with our eyes, because we know they aren’t seeing the whole picture (literally!). For this reason, we will use computer programs and packages (Mica package of ImageJ) to analyze the differences in these raw images. Then we might have a lead on what hummingbirds are seeing that is special about these underwing patches.
We are having lots of fun developing methods and trying out new programs to accomplish the novel goal of this project! One of our other goals with this project besides collecting research-grade data is communicating this with the public. We are conducting this work in an “activation” space of the museum, with high visibility to the public and have created a supplementary infographic to help the public understand what it is that we are doing. One of our greatest goals at the Behavioral Ecophysics Lab is to never get too far from the “why?” of the project, and we always want to communicate that to others, as well. To the public, it might look like we’re just taking pictures of the wings, but with a little background we can explain this multi-faceted project with behavioral insights and shed light on a new layer of communication.