Visual system and feeder use behavior of American goldfinches: Implications for the development of visually salient bird feeders

Patrice E Baumhardt, Purdue University

Abstract

One of the challenges for conservation biologists is to modify the behavior of species of concern (e.g., threatened species, pests) to either attract them to or repel them from a given location. This is generally done with artificial stimuli (e.g., decoys, colors, etc.) but without taking into consideration the sensory system of the target species. This problem becomes particularly relevant in birds as they have a visual system that is different from that of humans. Bird feeders can be an interesting study system for attracting birds to a visual stimulus because they are food sources during both the non-breeding and breeding seasons. The goal of this study was to investigate the visual system and foraging behavior of American goldfinches (Carduelis tristis ) to derive principles for the development of bird feeders that are visually salient for the sensory system of this species. I measured the spectral sensitivity of the American goldfinch visual pigments and oil droplets with microspectrophotometry, the location and type of retinal specialization with topographic variations in the density of retinal ganglion cells and photoreceptors, and the visual field configuration and degree of eye movement with an ophthalmoscopic reflex technique. Additionally, I conducted a behavioral experiment in an outdoor aviary by exposing American goldfinches to three differently colored bird feeders (green, yellow, red) and measuring the proportion of time spent in each of them. American goldfinches have a tetrachromatic ultra-violet visual system with peak sensitivities of 398 nm, 446 nm, 510 nm, and 575 nm. Goldfinches have a fovea that is centro-temporally located, projecting into the frontal part of the visual field. They also have large binocular (46°) and lateral (134°) visual fields with a high degree of eye movement (66° at the plane of the bill). In the aviary experiment, American goldfinches spent proportionally more time in the green feeder than in the yellow and red feeders. From the perspective of their visual system, green feeders were less visually salient than yellow and red feeders. This suggests that goldfinches may be more attracted to colors that are generally found in the environment (green leaves) or to colors that are not as salient visually. Based on these results, I propose a bird feeder that consists of a wire-mesh sphere containing seeds and sustained with a metal pole. This design would allow for easy access to food as well as provide an unobstructed view of the surroundings for goldfinches to scan for potential predators. The color of the sphere should be either green or another color with low contrast (brown, blue, or violet) from the American goldfinch visual system perspective. This study demonstrates that the understanding of the visual physiology and foraging behavior of a species can be used to design visual stimuli that can help manipulate the behavior of individuals in the wild.

Degree

M.S.

Advisors

Fernandez-Juricic, Purdue University.

Subject Area

Wildlife Management|Ecology

COinS