title: The Role of Environmental Visual Noise on Decision-Making
Creators: name: Quentin, Jamison
Publisher: name: George Mason University
Year: 2024
Subjects: subject: Decision Making
subject: Visual Noise
subject: Bird Behavior
subject: Bird Vision
subject: Avian Brood Parasitism
subject: Avian Window Collisions

description: Birds are well known for having good vision. This is particularly true for color perception and in some cases, visual acuity. They rely on their visual systems to gather information about their surroundings and then use this information to navigate, forage, and avoid threats. Although avian vision is incredible in many respects, no system is perfect, and any visual information is subject to noise from various sources. Noise in visual information can occur both in the environment and at the neurons themselves (when visual information is processed). Therefore, understanding how noise impacts signal reception is crucial for our understanding of how birds make decisions based on visual stimuli. For a stimulus to be detected, it must be differentiable from its background. Thus, the strength of a signal must exceed the background noise. When signal-to-noise ratios are high, signals are more recognizable. While the role of neural noise has long been appreciated, fewer studies have explicitly explored the role of other environmental noise that can limit the detection of visual signals. This is likely because environments can be complex with noise at spatial and temporal levels that are hard to measure in the wild. In this thesis, I explore the role of noise on avian visual perception, using avian window collisions and avian brood parasitism as model systems. In both instances, birds must make decisions based on visual stimuli, where making incorrect choices can have negative fitness consequences. Avian window collisions are a prime example of how decisions based on visual stimuli can lead to mortality. These collisions cause an astounding amount of mortality each year. Although there are several reasons why a bird might collide with a window, reflections on the window's surface are one of the main purported reasons. Birds may strike windows if they cannot recognize the difference between reflected and actual habitats. An inability to differentiate the reflected scene from the reflective object (the window) may result in attempts to fly toward elements in these reflected scenes, causing a window collision. While there has been much research into why avian window collisions happen and how to best mitigate them, no one has measured the level of reflection of the windows and related it to window collision mortality. In this study, I set out to determine whether windows with stronger and clearer reflections were more likely to be struck than windows with weaker and less clear reflections. I found that buildings with glossier surfaces, clearer reflections, and more window coverage had a higher chance of being struck. This has important implications for how people may mitigate window collisions. Another system where noise can impact decision-making and fitness is avian brood parasitism. Obligate avian brood parasitism occurs when a parasite lays its eggs in the nest of a heterospecific. In doing so, the parasite transfers the cost of nestling care to the host, which accrues fitness costs due to intrabrood competition or even the killing of its own young. Since hosts can suffer serious fitness costs from raising the parasite’s young, it is expected that they would evolve mechanisms to avoid parasitism. Indeed, some host species reject parasitic eggs by ejecting them from their nests. However, rejection rates vary between, and even within, species. One reason for variation in rejection rates within species could be noise in the environment, such as dappled light, which is caused by light passing through gaps in vegetation, creating patterns of light and shadow that can create confusion. This noise can be enhanced if the vegetation is moving, creating a dynamic background. While prior research has shown that these types of environmental noise can complicate decision-making by masking signals in the environment, this question has not yet been addressed in the avian brood parasitism system. Here, I hypothesized that hosts of a brood parasite will be more likely to reject a parasitic egg when there is a limited amount of dappled light, and there is no dynamic background. These conditions are stable and should facilitate decision-making. By contrast, hosts will be more likely to accept a foreign egg when their light environment is variable due to dappled light and dynamic backgrounds. These conditions can make decision-making more challenging. Alternatively, they may also accept eggs because they lack recognition ability, even when nesting under stable light environments. As a result, acceptors should be found across a wide range of light environments. I found that acceptors nested in habitats with more variable light environments, while rejectors nested in habitats with less variable light conditions, and were only found in low-noise light environments. This shows that noise is one of the factors affecting whether birds can reject parasitic eggs. In this thesis, I examined two examples of noise and how it can affect decision-making in birds. I found that window collisions are caused in part by strong reflections giving false signals that birds perceive as unobstructed openings. Likewise, I found that noise from the environment caused by dappled light and dynamic backgrounds can cause birds to accept parasitic eggs. Both of these studies highlight how noise can impair a bird’s ability to make decisions, and in both cases, suboptimal decisions lead to reduced fitness. Thus, my research opens the door to addressing new questions about noise and decision-making in wild birds.